使用Java解析class字节码结构

按照JVM 字节码的存储格式 https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html 规范，实现了一段程序解析字节码结构。

结果输出

========== Start Parse=========
== Magic Number ======================================
MagicNumber{b1=CA, b2=FE, b3=BA, b4=BE}
== Version ======================================
Version{minorVersion=0, majorVersion=52}
== Constant Pool ======================================
ConstantPool{poolCount=214, constantsSize=2376, mConstantItems=
  #1 MethodRef{classInfoIndex=65, nameAndTypeIndex=130}
  #2 String{index=131}
  ...
  #213 Utf8{attributeLength=20, value='()Ljava/lang/String;'}
}
== Access Flags ======================================
AccessFlags: public,final,super,
bytecode.AccessFlags@27bc2616
== This class ======================================
ClassIndex{classInfoIndex=49 -> 171 -> bytecode/BytecodeParser}
== Super class ======================================
ClassIndex{classInfoIndex=65 -> 185 -> java/lang/Object}
== Interfaces ======================================
Interface count: 0
Interface Indexes: []
== Fields ======================================
FieldOrMethod{count=2, name='Fields', mEntities=[Entity{accessFlag=[Public,Static,], nameIndex=66, name=constantItemHashMap, descriptorIndex=67, attributesCount=1, mAttributeInfos=[AttributeInfo{nameIndex=68, attributeLength=2, mInfo=Signature{signatureIndex=69 -> Ljava/util/HashMap<Ljava/lang/Integer;Lbytecode/ConstantItem;>;}}]}, Entity{accessFlag=[Private,Static,Final,], nameIndex=70, name=path, descriptorIndex=71, attributesCount=1, mAttributeInfos=[AttributeInfo{nameIndex=72, attributeLength=2, mInfo=ConstantValue{constantValueIndex=4}}]}]}
== Methods ======================================
FieldOrMethod{count=4, name='Methods', mEntities=[Entity{accessFlag=[Public,], nameIndex=73,...
== This class attribute_info ======================================
[AttributeInfo{nameIndex=128, attributeLength=2, mInfo=SourceFile{sourceFileIndex=129 -> BytecodeParser.java}}]

实现

整体流程

ClassFile {
    u4             magic;
    u2             minor_version;
    u2             major_version;
    u2             constant_pool_count;
    cp_info        constant_pool[constant_pool_count-1];
    u2             access_flags;
    u2             this_class;
    u2             super_class;
    u2             interfaces_count;
    u2             interfaces[interfaces_count];
    u2             fields_count;
    field_info     fields[fields_count];
    u2             methods_count;
    method_info    methods[methods_count];
    u2             attributes_count;
    attribute_info attributes[attributes_count];
}

按照字节码的储存顺序依次解析每一块内容。所有解析过程都共用一个 byte[] 数组，每个具体的解析过程，通过控制 offset 实现解析不同部分的数据。

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64


public final class BytecodeParser {
    // 用来在常量池解析完之后，存在全局方便后面使用
    public static HashMap<Integer, ConstantItem> constantItemHashMap;

    private void parse(final byte[] bytes) {
        printSectionDivider("Magic Number");
        Section magicNumber = new MagicNumber(0, bytes);
        magicNumber.parse();
        System.out.println(magicNumber);

        printSectionDivider("Version");
        Section version = new Version(magicNumber.end(), bytes);
        version.parse();
        System.out.println(version);

        printSectionDivider("Constant Pool");
        ConstantPool constantPool = new ConstantPool(version.end(), bytes);
        constantPool.parse();
        System.out.println(constantPool);
        constantItemHashMap = constantPool.getConstantItems();

        printSectionDivider("Access Flags");
        Section accessFlags = new AccessFlags(constantPool.end(), bytes);
        accessFlags.parse();
        System.out.println(accessFlags);

        printSectionDivider("This class");
        Section thisClass = new ClassIndex(accessFlags.end(), bytes);
        thisClass.parse();
        System.out.println(thisClass);

        printSectionDivider("Super class");
        Section superClass = new ClassIndex(thisClass.end(), bytes);
        superClass.parse();
        System.out.println(superClass);

        printSectionDivider("Interfaces");
        Interfaces interfaces = new Interfaces(superClass.end(), bytes);
        interfaces.parse();
        System.out.println(interfaces);

        printSectionDivider("Fields");
        FieldOrMethod fields = new FieldOrMethod("Fields", interfaces.end(), bytes);
        fields.parse();
        System.out.println(fields);

        printSectionDivider("Methods");
        FieldOrMethod methods = new FieldOrMethod("Methods", fields.end(), bytes);
        methods.parse();
        System.out.println(methods);

        printSectionDivider("This class attribute_info");
        int offset = methods.end();
        int attributeCount = Utils.read2Number(bytes, offset);
        offset += 2;
        AttributeInfo[] attributeInfos = new AttributeInfo[attributeCount];
        for (int i = 0; i < attributeCount; i++) {
            attributeInfos[i] = new AttributeInfo();
            attributeInfos[i].parse(bytes, offset);
            offset += attributeInfos[i].size();
        }
        System.out.println(Arrays.toString(attributeInfos));
    }
}

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23


public static void main(String[] args) {
    if (args.length < 1) {
        throw new IllegalArgumentException("Must pass class file path.");
    }
    String path = args[0];
    System.out.println("========== Start Parse=========");
    try {
        FileInputStream fis = new FileInputStream(new File(path));
        int count = fis.available();
        byte[] buff = new byte[count];
        int read = fis.read(buff);
        if (read != count) {
            return;
        }
        new BytecodeParser().parse(buff);
    } catch (IOException e) {
        e.printStackTrace();
    }
}

private static void printSectionDivider(String name) {
    System.out.println("== " + name + " ======================================");
}

提取了一些抽象

方便后面实现时生成统一的方法

1
2
3


interface Parsable {
    public void parse(byte[] bytes, int offset);
}

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21


abstract class Section {
    final int start;    //记录每一块结构的开始位置
    final byte[] bytes; // 所有人共用的数据

    public Section(int start, byte[] bytes) {
        this.start = start;
        this.bytes = bytes;
    }

    public final int start() {
        return start;
    }

    public final int end() {
        return start + size();
    }

    abstract int size();    //每一块结构需要返回自己占用了多少字节

    abstract public void parse();
}

解析魔数

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31


class MagicNumber extends Section {

    public MagicNumber(int start, byte[] bytes) {
        super(start, bytes);
    }

    @Override
    int size() {
        return 4;
    }

    private int b1, b2, b3, b4;//u1

    @Override
    public void parse() {
        b1 = Utils.readUnsignedByte(bytes, start);
        b2 = Utils.readUnsignedByte(bytes, start + 1);
        b3 = Utils.readUnsignedByte(bytes, start + 2);
        b4 = Utils.readUnsignedByte(bytes, start + 3);
    }

    @Override
    public String toString() {
        return "MagicNumber{" +
                "b1=" + Integer.toHexString(b1).toUpperCase() +
                ", b2=" + Integer.toHexString(b2).toUpperCase() +
                ", b3=" + Integer.toHexString(b3).toUpperCase() +
                ", b4=" + Integer.toHexString(b4).toUpperCase() +
                '}';
    }
}

解析版本号

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27


class Version extends Section {

    public Version(int start, byte[] bytes) {
        super(start, bytes);
    }

    @Override
    int size() {
        return 4;
    }

    private int minorVersion, majorVersion; //u2

    @Override
    public void parse() {
        minorVersion = Utils.read2Number(bytes, start);
        majorVersion = Utils.read2Number(bytes, start + 2);
    }

    @Override
    public String toString() {
        return "Version{" +
                "minorVersion=" + minorVersion +
                ", majorVersion=" + majorVersion +
                '}';
    }
}

解析常量池

常量池这里有一点要注意：代表常量池有多少常量的 poolCount，是包括了 poolCount 它本身的。也就是真正的常量池的常量其实是 poolCount -1 个。

每个常量项都有一个 u1 的 tag 表示其类型。解析时需要先解析 tag, 然后根据 tag 做对应类型的解析。

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53


class ConstantPool extends Section {

    int poolCount; //u2
    private int constantsSize;

    private HashMap<Integer, ConstantItem> mConstantItems = new HashMap<>();

    public HashMap<Integer, ConstantItem> getConstantItems() {
        return mConstantItems;
    }

    public ConstantPool(int start, byte[] bytes) {
        super(start, bytes);
    }

    @Override
    int size() {
        return 2/*u2 的常量池计数占用*/ + constantsSize;
    }

    @Override
    public void parse() {
        poolCount = Utils.read2Number(bytes, start);
        // 遍历常量表的每一项常量
        int offset = 2;
        for (int i = 1; i <= poolCount - 1; i++) {
            int tag = Utils.readUnsignedByte(bytes, start + offset);
            // 根据 tag 找到匹配的常量
            ConstantItem item = ConstantItem.getConstantItemTags(tag);
            if (item == null) {
                System.err.println("Not found ConstantItem for " + tag);
                return;
            }
            item.parse(bytes, start + offset);
            offset += item.size();
            constantsSize += item.size();
            mConstantItems.put(i, item);
        }
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        for (int i = 1; i <= poolCount - 1; i++) {
            sb.append("  #").append(i).append(" ").append(mConstantItems.get(i)).append("\n");
        }
        return "ConstantPool{" +
                "poolCount=" + poolCount +
                ", constantsSize=" + constantsSize +
                ", mConstantItems=\n" + sb.toString() +
                '}';
    }
}

每个常量项

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60


/**
 * 常量项
 * 每个常量项都有 u1 的 tag, 表示其类型
 * <pre>
 * cp_info {
 *     u1 tag;
 *     u1 info[];
 * }
 * </pre>
 */
abstract class ConstantItem implements Parsable {
    final int tag;

    ConstantItem(int tag) {
        this.tag = tag;
    }

    abstract protected int contentSize();

    int size() {
        return 1/*u1的tag*/ + contentSize();
    }

    @Nullable
    static ConstantItem getConstantItemTags(int tag) {
        switch (tag) {
            case 1:
                return new UTF8();
            case 3:
                return new INTEGER();
            case 4:
                return new FLOAT();
            case 5:
                return new LONG();
            case 6:
                return new DOUBLE();
            case 7:
                return new CLASS();
            case 8:
                return new STRING();
            case 9:
                return new FIELD_REF();
            case 10:
                return new METHOD_REF();
            case 11:
                return new Interface_Method_Ref();
            case 12:
                return new NAME_AND_TYPE();
            case 15:
                return new Method_Handle();
            case 16:
                return new Method_Type();
            case 18:
                return new Invoke_Dynamic();
            default:
                return null;
        }
    }

}

CONSTANT_Utf8

所有的字面量都储存在 UTF8 常量中。value 存储着以 UTF-8 编码的字符串的原始字节数据。

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29


//region Constants

class UTF8 extends ConstantItem {
    private int length;
    public String value;

    UTF8() {
        super(1);
    }

    @Override
    protected int contentSize() {
        return length /* 字符串占用的字节数 */ + 2 /* u2 的字符串长度 attributeLength*/;
    }

    @Override
    public void parse(byte[] bytes, int start) {
        length = Utils.read2Number(bytes, start + 1);
        value = new String(bytes, start + 3, length);
    }

    @Override
    public String toString() {
        return "Utf8{" +
                "attributeLength=" + length +
                ", value='" + value + '\'' +
                '}';
    }
}

CONSTANT_Integer

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24


class INTEGER extends ConstantItem {
    int value;

    protected INTEGER() {
        super(3);
    }

    @Override
    protected int contentSize() {
        return 4 /*u4 值*/;
    }

    @Override
    public void parse(byte[] bytes, int start) {
        value = Utils.read4Number(bytes, start + 1);
    }

    @Override
    public String toString() {
        return "Integer{" +
                "value=" + value +
                '}';
    }
}

CONSTANT_Float

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24


class FLOAT extends ConstantItem {
    float value;

    FLOAT() {
        super(4);
    }

    @Override
    protected int contentSize() {
        return 4 /* 同 INTEGER 的注释 */;
    }

    @Override
    public void parse(byte[] bytes, int start) {
        value = Utils.read4Number(bytes, start + 1);
    }

    @Override
    public String toString() {
        return "Float{" +
                "value=" + value +
                '}';
    }
}

CONSTANT_Long

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24


class LONG extends ConstantItem {
    long value;

    LONG() {
        super(5);
    }

    @Override
    protected int contentSize() {
        return 8 /* u8 值*/;
    }

    @Override
    public void parse(byte[] bytes, int start) {
        value = Utils.read8Number(bytes, start + 1);
    }

    @Override
    public String toString() {
        return "Long{" +
                "value=" + value +
                '}';
    }
}

CONSTANT_Double

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25


class DOUBLE extends ConstantItem {

    DOUBLE() {
        super(6);
    }

    double value;

    @Override
    protected int contentSize() {
        return 8 /*u8 值*/;
    }

    @Override
    public void parse(byte[] bytes, int start) {
        value = Utils.read8Number(bytes, start + 1);
    }

    @Override
    public String toString() {
        return "Double{" +
                "value=" + value +
                '}';
    }
}

CONSTANT_Class

存储指向类的全限定名在常量池中的索引 index

class CLASS extends ConstantItem {

    CLASS() {
        super(7);
    }

    int index;

    @Override
    protected int contentSize() {
        return 2 /*u2 常量池索引*/;
    }

    @Override
    public void parse(byte[] bytes, int start) {
        index = Utils.read2Number(bytes, start + 1);
    }

    @Override
    public String toString() {
        return "Class{" +
                "index=" + index +
                '}';
    }
}

CONSTANT_String

存储指向 Constant_UTF8 的索引 index

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24


class STRING extends ConstantItem {
    STRING() {
        super(8);
    }

    int index; //u2

    @Override
    protected int contentSize() {
        return 2/*u2 常量池索引*/;
    }

    @Override
    public void parse(byte[] bytes, int start) {
        index = Utils.read2Number(bytes, start + 1);
    }

    @Override
    public String toString() {
        return "String{" +
                "index=" + index +
                '}';
    }
}

CONSTANT_Fieldref

classInfoIndex 声明字段的类的信息，指向 CONSTANT_Class
nameAndTypeIndex 字段的信息，指向 CONSTANT_NameAndType 类型的索引

class FIELD_REF extends ConstantItem {

    int classInfoIndex, nameAndTypeIndex;

    FIELD_REF() {
        super(9);
    }

    @Override
    protected int contentSize() {
        return 2/*u2 类信息常量池索引*/ + 2/*u2 名字和类型常量池索引*/;
    }

    @Override
    public void parse(byte[] bytes, int start) {
        classInfoIndex = Utils.read2Number(bytes, start + 1);
        nameAndTypeIndex = Utils.read2Number(bytes, start + 3);
    }

    @Override
    public String toString() {
        return "FileRef{" +
                "classInfoIndex=" + classInfoIndex +
                ", nameAndTypeIndex=" + nameAndTypeIndex +
                '}';
    }
}

CONSTANT_Methodref

classInfoIndex 声明方法的类的信息，指向 CONSTANT_Class
nameAndTypeIndex 方法的信息，指向 CONSTANT_NameAndType 类型的索引

class METHOD_REF extends ConstantItem {
    int classInfoIndex, nameAndTypeIndex;

    METHOD_REF() {
        super(10);
    }

    @Override
    protected int contentSize() {
        return 4 /*同 FIELD_REF*/;
    }

    @Override
    public void parse(byte[] bytes, int start) {
        classInfoIndex = Utils.read2Number(bytes, start + 1);
        nameAndTypeIndex = Utils.read2Number(bytes, start + 3);
    }

    @Override
    public String toString() {
        return "MethodRef{" +
                "classInfoIndex=" + classInfoIndex +
                ", nameAndTypeIndex=" + nameAndTypeIndex +
                '}';
    }
}

CONSTANT_InterfaceMethodref

classInfoIndex 声明接口的类的信息，指向 CONSTANT_Class
nameAndTypeIndex 接口的信息，指向 CONSTANT_NameAndType 类型的索引

class Interface_Method_Ref extends ConstantItem {
    int classInfoIndex, nameAndTypeIndex;

    Interface_Method_Ref() {
        super(11);
    }

    @Override
    protected int contentSize() {
        return 4/*同FIELD_REF*/;
    }

    @Override
    public void parse(byte[] bytes, int start) {
        classInfoIndex = Utils.read2Number(bytes, start + 1);
        nameAndTypeIndex = Utils.read2Number(bytes, start + 3);
    }

    @Override
    public String toString() {
        return "InterfaceMethodRef{" +
                "classInfoIndex=" + classInfoIndex +
                ", nameAndTypeIndex=" + nameAndTypeIndex +
                '}';
    }
}

CONSTANT_NameAndType

nameIndex 指向方法或字段的名称在常量池中的索引
descriptorIndex 指向方法或字段的描述符在常量池中的索引

class NAME_AND_TYPE extends ConstantItem {
    int nameIndex, descriptorIndex; //u2

    NAME_AND_TYPE() {
        super(12);
    }

    @Override
    protected int contentSize() {
        return 2/*u2 名称在常量池的索引*/ + 2/*u2 描述符在常量池的索引*/;
    }

    @Override
    public void parse(byte[] bytes, int start) {
        nameIndex = Utils.read2Number(bytes, start + 1);
        descriptorIndex = Utils.read2Number(bytes, start + 3);
    }

    @Override
    public String toString() {
        return "NameAndType{" +
                "nameIndex=" + nameIndex +
                ", descriptorIndex=" + descriptorIndex +
                '}';
    }
}

CONSTANT_MethodHandle

详细信息参考 https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html#jvms-4.4.8

referenceKind 方法句柄的类型，代表字节码被执行时的行为. ? 不太懂这个… 还没有遇到出现的情况
referenceIndex

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28


class Method_Handle extends ConstantItem {

    int referenceKind; //u1
    int referenceIndex; //u2

    Method_Handle() {
        super(15);
    }

    @Override
    protected int contentSize() {
        return 1/**/ + 2/**/;
    }

    @Override
    public void parse(byte[] bytes, int start) {
        referenceKind = Utils.readUnsignedByte(bytes, start + 1);
        referenceIndex = Utils.read2Number(bytes, start + 2);
    }

    @Override
    public String toString() {
        return "MethodHandle{" +
                "referenceKind=" + referenceKind +
                ", referenceIndex=" + referenceIndex +
                '}';
    }
}

CONSTANT_MethodType

descriptorIndex 指向常量池中 UTF8 类型的索引，表示方法的描述符

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24


class Method_Type extends ConstantItem {
    int descriptorIndex; //u2

    Method_Type() {
        super(16);
    }

    @Override
    protected int contentSize() {
        return 2;
    }

    @Override
    public void parse(byte[] bytes, int start) {
        descriptorIndex = Utils.read2Number(bytes, start + 1);
    }

    @Override
    public String toString() {
        return "MethodType{" +
                "descriptorIndex=" + descriptorIndex +
                '}';
    }
}

CONSTANT_InvokeDynamic

https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html#jvms-4.4.10

与 Java 的动态方法调用有关。

class Invoke_Dynamic extends ConstantItem {
    int bootstrapAttrIndex, nameAndTypeIndex;

    Invoke_Dynamic() {
        super(18);
    }

    @Override
    protected int contentSize() {
        return 4;
    }

    @Override
    public void parse(byte[] bytes, int start) {
        bootstrapAttrIndex = Utils.read2Number(bytes, start + 1);
        nameAndTypeIndex = Utils.read2Number(bytes, start + 3);
    }

    @Override
    public String toString() {
        return "InvokeDynamic{" +
                "bootstrapAttrIndex=" + bootstrapAttrIndex +
                ", nameAndTypeIndex=" + nameAndTypeIndex +
                '}';
    }
}

//endregion

解析访问标志

一个字段或方法或类的访问标志都是使用一个 u2 类型的数字表示，通过位运算 | 赋予，通过 &运算判断是否拥有某种访问标志。

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63


class AccessFlags extends Section {

    private static final int PUBLIC = 0x0001;    // 0000 0000 0000 0001
    private static final int FINAL = 0x0010;     // 0000 0000 0001 0000
    private static final int SUPER = 0x0020;     // 0000 0000 0010 0000
    private static final int INTERFACE = 0x0200; // 0000 0010 0000 0000
    private static final int ABSTRACT = 0x0400;  // 0000 0100 0000 0000
    private static final int SYNTHETIC = 0x1000; // 0001 0000 0000 0000
    private static final int ANNOTATION = 0x2000;// 0010 0000 0000 0000
    private static final int ENUM = 0x4000;      // 0100 0000 0000 0000
    private static final int PRIVATE = 0x0002;

    private int accessFlags; //u2

    public AccessFlags(int start, byte[] bytes) {
        super(start, bytes);
    }

    @Override
    int size() {
        return 2;
    }

    @Override
    public void parse() {
        accessFlags = Utils.read2Number(bytes, start);
        System.out.println("AccessFlags: " + printAccess(accessFlags));
    }

    public static String printAccess(int access) {
        ArrayList<String> accessFlags = new ArrayList<>();
        if ((access & PUBLIC) == PUBLIC) {
            accessFlags.add("public");
        }
        if ((access & FINAL) == FINAL) {
            accessFlags.add("final");
        }
        if ((access & SUPER) == SUPER) {
            accessFlags.add("super");
        }
        if ((access & INTERFACE) == INTERFACE) {
            accessFlags.add("interface");
        }
        if ((access & ABSTRACT) == ABSTRACT) {
            accessFlags.add("abstract");
        }
        if ((access & SYNTHETIC) == SYNTHETIC) {
            accessFlags.add("synthetic");
        }
        if ((access & ANNOTATION) == ANNOTATION) {
            accessFlags.add("annotation");
        }
        if ((access & ENUM) == ENUM) {
            accessFlags.add("enum");
        }
        if ((access & PRIVATE) == PRIVATE) {
            accessFlags.add("private");
        }
        StringBuilder sb = new StringBuilder();
        accessFlags.forEach(s -> sb.append(s).append(","));
        return sb.toString();
    }
}

解析类信息

类自身和其父类都存储在 class_info 结构中，classInfoIndex 指向常量池中 Constant_Class 类型的常量

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32


/**
 * 类索引
 * 用于解析自身类和父类在常量池的索引
 */
class ClassIndex extends Section {

    private int classInfoIndex;

    public ClassIndex(int start, byte[] bytes) {
        super(start, bytes);
    }

    @Override
    int size() {
        return 2;
    }

    @Override
    public void parse() {
        classInfoIndex = Utils.read2Number(bytes, start);
    }

    @Override
    public String toString() {
        CLASS clasz = (CLASS) BytecodeParser.constantItemHashMap.get(classInfoIndex);
        UTF8 utf8 = (UTF8) BytecodeParser.constantItemHashMap.get(clasz.index);
        return "ClassIndex{" +
                "classInfoIndex=" + classInfoIndex +
                " -> " + clasz.index + " -> " + utf8.value +
                '}';
    }
}

解析接口

类实现的所有接口在常量池的 Constant_class 类型索引

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33


class Interfaces extends Section {

    int interfaceCount; //u2
    int[] indexs; // u2[interfaceCount]

    public Interfaces(int start, byte[] bytes) {
        super(start, bytes);
    }

    @Override
    int size() {
        return interfaceCount * 2 + 2;
    }

    @Override
    public void parse() {
        interfaceCount = Utils.read2Number(bytes, start);
        int offset = 2;
        indexs = new int[interfaceCount];
        for (short i = 0; i < interfaceCount; i++) {
            int index = Utils.read2Number(bytes, start + offset);
            indexs[i] = index;
        }
    }

    @Override
    public String toString() {
        return "Interfaces{" +
                "interfaceCount=" + interfaceCount +
                ", indexs=" + Arrays.toString(indexs) +
                '}';
    }
}

解析方法和字段

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141


/**
 * <pre>
 * field_info {
 *     u2             access_flags;
 *     u2             name_index;
 *     u2             descriptor_index;
 *     u2             attributes_count;
 *     attribute_info attributes[attributes_count];
 * }
 * </pre>
 */
class FieldOrMethod extends Section {

    private int infoSize = 0;

    int count; //u2

    static class Entity {

        int accessFlag;  //u2
        int nameIndex;   //u2
        int descriptorIndex; //u2
        int attributesCount; //u2

        private ArrayList<AttributeInfo> mAttributeInfos = new ArrayList<>();

        public int size() {
            int infoSize = 0;
            for (AttributeInfo info : mAttributeInfos) {
                infoSize += info.size();
            }
            return 8 + infoSize;
        }

        public void parse(byte[] bytes, int offset) {
            accessFlag = Utils.read2Number(bytes, offset);
            offset += 2;
            nameIndex = Utils.read2Number(bytes, offset);
            offset += 2;
            descriptorIndex = Utils.read2Number(bytes, offset);
            offset += 2;
            attributesCount = Utils.read2Number(bytes, offset);
            offset += 2;
            for (int i = 0; i < attributesCount; i++) {
                AttributeInfo attributeInfo = new AttributeInfo();
                attributeInfo.parse(bytes, offset);
                mAttributeInfos.add(attributeInfo);
                offset += attributeInfo.size();
            }
        }

        static final int PUBLIC = 0x0001;
        static final int PRIVATE = 0x0002;
        static final int PROTECTED = 0x0004;
        static final int STATIC = 0x0008;
        static final int FINAL = 0x0010;
        // field special
        static final int VOLATILE = 0x0040;
        static final int TRANSIENT = 0x0080;
        static final int SYNTHETIC = 0x1000;
        static final int ENUM = 0x4000;
        // method special
        static final int SYNCHRONIZED = 0x0020;
        static final int BRIDGE = 0x0040;
        static final int VARARGS = 0x0080;
        static final int NATIVE = 0x0100;
        static final int ABSTRACT = 0x0400;
        static final int STRICTFP = 0x0500;

        private static String accessFlagReadable(int access) {
            StringBuilder sb = new StringBuilder();
            sb.append("[");
            if ((access & PUBLIC) == PUBLIC) sb.append("Public,");
            if ((access & PRIVATE) == PRIVATE) sb.append("Private,");
            if ((access & PROTECTED) == PROTECTED) sb.append("Protected,");
            if ((access & STATIC) == STATIC) sb.append("Static,");
            if ((access & FINAL) == FINAL) sb.append("Final,");
            if ((access & VOLATILE) == VOLATILE) sb.append("Volatile,");
            if ((access & TRANSIENT) == TRANSIENT) sb.append("Transient,");
            if ((access & SYNTHETIC) == SYNTHETIC) sb.append("Synthetic,");
            if ((access & ENUM) == ENUM) sb.append("Enum,");
            if ((access & SYNCHRONIZED) == SYNCHRONIZED) sb.append(", Synchronized");
            if ((access & BRIDGE) == BRIDGE) sb.append(",Bridge");
            if ((access & VARARGS) == VARARGS) sb.append(",Varargs");
            if ((access & NATIVE) == NATIVE) sb.append(",Native");
            if ((access & ABSTRACT) == ABSTRACT) sb.append(",Abstract");
            if ((access & STRICTFP) == STRICTFP) sb.append(",Strictfp");

            sb.append("]");
            return sb.toString();
        }

        @Override
        public String toString() {
            return "Entity{" +
                    "accessFlag=" + accessFlagReadable(accessFlag) +
                    ", nameIndex=" + nameIndex +
                    ", name=" + ((UTF8) BytecodeParser.constantItemHashMap.get(nameIndex)).value +
                    ", descriptorIndex=" + descriptorIndex +
                    ", attributesCount=" + attributesCount +
                    ", mAttributeInfos=" + mAttributeInfos +
                    '}';
        }
    }

    private final String name;
    private final ArrayList<Entity> mEntities = new ArrayList<>();

    public FieldOrMethod(String name, int start, byte[] bytes) {
        super(start, bytes);
        this.name = name;
    }

    @Override
    int size() {
        return infoSize + 2;
    }

    @Override
    public void parse() {
        int offset = start;
        count = Utils.read2Number(bytes, offset);
        offset += 2;
        for (int i = 0; i < count; i++) {
            Entity entity = new Entity();
            entity.parse(bytes, offset);
            mEntities.add(entity);
            infoSize += entity.size();
            offset += entity.size();
        }
    }

    @Override
    public String toString() {
        return "FieldOrMethod{" +
                "count=" + count +
                ", name='" + name + '\'' +
                ", mEntities=" + mEntities +
                '}';
    }
}

解析属性表

字段、方法、类都能拥有自己的属性表。只是某些属性只会出现在字段上(比如 volatile)或方法上(比如 synchronized)。

u2 attribute_name_index;
u4 attribute_length;

attribute_name_index 和 attribute_length 是每个属性都有的两个字段，所以提出来由父类实现解析。

/**
 * <pre>
 * attribute_info {
 *     u2 attribute_name_index;
 *     u4 attribute_length;
 *     u1 info[attribute_length];
 * }
 * </pre>
 */
class AttributeInfo implements Parsable {
    private int nameIndex;  //u2
    private int attributeLength; //u4
    private Info mInfo;

    @Override
    public void parse(byte[] bytes, int offset) {
        nameIndex = Utils.read2Number(bytes, offset);
        offset += 2;
        attributeLength = Utils.read4Number(bytes, offset);
        offset += 4;
        // 根据属性名称找到匹配的属性
        ConstantItem constantItem = BytecodeParser.constantItemHashMap.get(nameIndex);
        UTF8 utf8 = (UTF8) constantItem;
        String infoName = utf8.value;
        mInfo = Info.getMatchInfo(infoName);
        if (mInfo == null) {
            System.err.println("Not found matching Attributes: " + infoName);
            return;
        }
        mInfo.parse(bytes, offset);
    }

    public int size() {
        return 2 + 4 + attributeLength;
    }

    @Override
    public String toString() {
        return "AttributeInfo{" +
                "nameIndex=" + nameIndex +
                ", attributeLength=" + attributeLength +
                ", mInfo=" + mInfo +
                '}';
    }
}

abstract class Info implements Parsable {
    public int size() {
        return contentSize();
    }

    abstract protected int contentSize();

    abstract public void parseInner(byte[] bytes, int offset);

    @Override
    public void parse(byte[] bytes, int offset) {
        parseInner(bytes, offset);
    }

    @Nullable
    public static Info getMatchInfo(String name) {
        switch (name) {
            case "Code":
                return new CodeInfo();
            case "ConstantValue":
                return new ConstantValue();
            case "Exceptions":
                return new Exceptions();
            case "LineNumberTable":
                return new LineNumberTable();
            case "LocalVariableTable":
                return new LocalVariableTable();
            case "LocalVariableTypeTable":
                return new LocalVariableTypeTable();
            case "SourceFile":
                return new SourceFile();
            case "InnerClasses":
                return new InnerClasses();
            case "Deprecated":
                return new Deprecated();
            case "Synthetic":
                return new Synthetic();
            case "StackMapTable":
                // TODO StackMapTable 待实现
                return null;
            case "Signature":
                return new Signature();
            default:
                return null;
        }
    }
}

Code 属性

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116


//region Info
/**
 * <pre>
 * Code_attribute {
 *     u2 attribute_name_index;
 *     u4 attribute_length;
 *     u2 max_stack;
 *     u2 max_locals;
 *     u4 code_length;
 *     u1 code[code_length];
 *     u2 exception_table_length;
 *     {   u2 start_pc;
 *         u2 end_pc;
 *         u2 handler_pc;
 *         u2 catch_type;
 *     } exception_table[exception_table_length];
 *     u2 attributes_count;
 *     attribute_info attributes[attributes_count];
 * }
 * </pre>
 */
class CodeInfo extends Info {

    class ExceptionTable implements Parsable {
        int startPc; //u2
        int endPc; //u2
        int handlePc; // u2
        int catchType; //u2

        public int size() {
            return 2 + 2 + 2 + 2;
        }

        @Override
        public void parse(byte[] bytes, int offset) {
            startPc = Utils.read2Number(bytes, offset);
            offset += 2;
            endPc = Utils.read2Number(bytes, offset);
            offset += 2;
            handlePc = Utils.read2Number(bytes, offset);
            offset += 2;
            catchType = Utils.read2Number(bytes, offset);
        }

        @Override
        public String toString() {
            return "ExceptionTable{" +
                    "startPc=" + startPc +
                    ", endPc=" + endPc +
                    ", handlePc=" + handlePc +
                    ", catchType=" + catchType +
                    '}';
        }
    }

    int maxStack; //u2
    int maxLocals; //u2
    int codeLength; //u4
    int[] code; // u1[codeLength]
    int exceptionTableLength; //u2
    ExceptionTable[] exceptionTable;
    int attributeCount; //u2
    AttributeInfo[] attributes;

    private int attributesSize;

    @Override
    public int contentSize() {
        return attributesSize + 2 + 2 + 4 + codeLength + exceptionTableLength;
    }

    @Override
    public void parseInner(byte[] bytes, int offset) {
        maxStack = Utils.read2Number(bytes, offset);
        offset += 2;
        maxLocals = Utils.read2Number(bytes, offset);
        offset += 2;
        codeLength = Utils.read4Number(bytes, offset);
        offset += 4;
        code = new int[codeLength];
        for (int i = 0; i < codeLength; i++) {
            code[i] = Utils.readUnsignedByte(bytes, offset);
            offset += 1;
        }
        exceptionTableLength = Utils.read2Number(bytes, offset);
        offset += 2;
        exceptionTable = new ExceptionTable[exceptionTableLength];
        for (int i = 0; i < exceptionTableLength; i++) {
            exceptionTable[i] = new ExceptionTable();
            exceptionTable[i].parse(bytes, offset);
            offset += exceptionTable[i].size();
        }
        attributeCount = Utils.read2Number(bytes, offset);
        offset += 2;
        attributes = new AttributeInfo[attributeCount];
        for (int i = 0; i < attributeCount; i++) {
            attributes[i] = new AttributeInfo();
            attributes[i].parse(bytes, offset);
            offset += attributes[i].size();
            attributesSize += attributes[i].size();
        }
    }

    public String toString() {
        return "CodeInfo{" +
                "maxStack=" + maxStack +
                ", maxLocals=" + maxLocals +
                ", codeLength=" + codeLength +
                ", code=" + Arrays.toString(code) +
                ", exceptionTableLength=" + exceptionTableLength +
                ", exceptionTable=" + Arrays.toString(exceptionTable) +
                ", attributeCount=" + attributeCount +
                ", attributes=" + Arrays.toString(attributes) +
                '}';
    }
}

常量属性

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20


class ConstantValue extends Info {
    int constantValueIndex; //u2

    @Override
    public void parseInner(byte[] bytes, int offset) {
        constantValueIndex = Utils.read2Number(bytes, offset + 2);
    }

    @Override
    public int contentSize() {
        return 2;
    }

    @Override
    public String toString() {
        return "ConstantValue{" +
                "constantValueIndex=" + constantValueIndex +
                '}';
    }
}

异常属性

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38


/**
 * <pre>
 * Exceptions_attribute {
 *     u2 attribute_name_index;
 *     u4 attribute_length;
 *     u2 number_of_exceptions;
 *     u2 exception_index_table[number_of_exceptions];
 * }
 * </pre>
 */
class Exceptions extends Info {
    int numberOfExceptions; //u2
    int[] exceptionIndexTable; //u2[numberOfExceptions]

    @Override
    public int contentSize() {
        return 2;
    }

    @Override
    public void parseInner(byte[] bytes, int offset) {
        numberOfExceptions = Utils.read2Number(bytes, offset);
        offset += 2;
        exceptionIndexTable = new int[numberOfExceptions];
        for (int i = 0; i < numberOfExceptions; i++) {
            exceptionIndexTable[i] = Utils.read2Number(bytes, offset);
            offset += 2;
        }
    }

    @Override
    public String toString() {
        return "Exceptions{" +
                "numberOfExceptions=" + numberOfExceptions +
                ", exceptionIndexTable=" + Arrays.toString(exceptionIndexTable) +
                '}';
    }
}

字节码与源码行号对应

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64


/**
 * <pre>
 * LineNumberTable_attribute {
 *     u2 attribute_name_index;
 *     u4 attribute_length;
 *     u2 line_number_table_length;
 *     {   u2 start_pc;
 *         u2 line_number;
 *     } line_number_table[line_number_table_length];
 * }
 * </pre>
 */
class LineNumberTable extends Info {

    class LineNumberInfo implements Parsable {
        int startPc; //u2
        int lineNumber; //u2

        public static final int size = 4;

        @Override
        public void parse(byte[] bytes, int offset) {
            startPc = Utils.read2Number(bytes, offset);
            offset += 2;
            lineNumber = Utils.read2Number(bytes, offset);
        }

        @Override
        public String toString() {
            return "LineNumberInfo{" +
                    "startPc=" + startPc +
                    ", lineNumber=" + lineNumber +
                    '}';
        }
    }

    int lineNumberTableLength; //u2
    private LineNumberInfo[] mLineNumberInfos;

    @Override
    protected int contentSize() {
        return mLineNumberInfos.length * LineNumberInfo.size + 2;
    }

    @Override
    public void parseInner(byte[] bytes, int offset) {
        lineNumberTableLength = Utils.read2Number(bytes, offset);
        offset += 2;
        mLineNumberInfos = new LineNumberInfo[lineNumberTableLength];
        for (int i = 0; i < lineNumberTableLength; i++) {
            mLineNumberInfos[i] = new LineNumberInfo();
            mLineNumberInfos[i].parse(bytes, offset);
            offset += LineNumberInfo.size;
        }
    }

    @Override
    public String toString() {
        return "LineNumberTable{" +
                "lineNumberTableLength=" + lineNumberTableLength +
                ", mLineNumberInfos=" + Arrays.toString(mLineNumberInfos) +
                '}';
    }
}

局部变量属性

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75


/**
 * <pre>
 * LocalVariableTable_attribute {
 *     u2 attribute_name_index;
 *     u4 attribute_length;
 *     u2 local_variable_table_length;
 *     {   u2 start_pc;
 *         u2 length;
 *         u2 name_index;
 *         u2 descriptor_index;
 *         u2 index;
 *     } local_variable_table[local_variable_table_length];
 * }
 * </pre>
 */
class LocalVariableTable extends Info {

    class LocalVairableTableItem implements Parsable {
        int startPc;
        int length;
        int nameIndex;
        int descriptorIndex;
        int index;

        public static final int size = 10;

        @Override
        public void parse(byte[] bytes, int offset) {
            startPc = Utils.read2Number(bytes, offset);
            length = Utils.read2Number(bytes, offset + 2);
            nameIndex = Utils.read2Number(bytes, offset + 2);
            descriptorIndex = Utils.read2Number(bytes, offset + 4);
            index = Utils.read2Number(bytes, offset + 6);
        }

        @Override
        public String toString() {
            return "LocalVairableTableItem{" +
                    "startPc=" + startPc +
                    ", length=" + length +
                    ", nameIndex=" + nameIndex +
                    ", descriptorIndex=" + descriptorIndex +
                    ", index=" + index +
                    '}';
        }
    }

    int localVariableTableLength; //u2
    private LocalVairableTableItem[] items;

    @Override
    protected int contentSize() {
        return localVariableTableLength * LocalVairableTableItem.size + 2;
    }

    @Override
    public void parseInner(byte[] bytes, int offset) {
        localVariableTableLength = Utils.read2Number(bytes, offset);
        offset += 2;
        items = new LocalVairableTableItem[localVariableTableLength];
        for (int i = 0; i < localVariableTableLength; i++) {
            items[i] = new LocalVairableTableItem();
            items[i].parse(bytes, offset);
            offset += LocalVairableTableItem.size;
        }
    }

    @Override
    public String toString() {
        return "LocalVariableTable{" +
                "localVariableTableLength=" + localVariableTableLength +
                ", items=" + Arrays.toString(items) +
                '}';
    }
}

源代码文件属性

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30


/**
 * <pre>
 * SourceFile_attribute {
 *     u2 attribute_name_index;
 *     u4 attribute_length;
 *     u2 sourcefile_index;
 * }
 * </pre>
 */
class SourceFile extends Info {

    int sourceFileIndex; //u2

    @Override
    protected int contentSize() {
        return 2;
    }

    @Override
    public void parseInner(byte[] bytes, int offset) {
        sourceFileIndex = Utils.read2Number(bytes, offset);
    }

    @Override
    public String toString() {
        return "SourceFile{" +
                "sourceFileIndex=" + sourceFileIndex + " -> " + ((UTF8) BytecodeParser.constantItemHashMap.get(sourceFileIndex)).value +
                '}';
    }
}

内部类属性

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71


/**
 * <pre>
 * InnerClasses_attribute {
 *     u2 attribute_name_index;
 *     u4 attribute_length;
 *     u2 number_of_classes;
 *     {   u2 inner_class_info_index;
 *         u2 outer_class_info_index;
 *         u2 inner_name_index;
 *         u2 inner_class_access_flags;
 *     } classes[number_of_classes];
 * }
 * </pre>
 */
class InnerClasses extends Info {

    class Classes implements Parsable {
        int innerClassInfoIndex, outerClassInfoIndex, innerNameInex, innerClassAccessFlags; //u2

        public static final int size = 8;

        @Override
        public void parse(byte[] bytes, int offset) {
            innerClassInfoIndex = Utils.read2Number(bytes, offset);
            offset += 2;
            outerClassInfoIndex = Utils.read2Number(bytes, offset);
            offset += 2;
            innerNameInex = Utils.read2Number(bytes, offset);
            offset += 2;
            innerClassAccessFlags = Utils.read2Number(bytes, offset);
        }

        @Override
        public String toString() {
            return "Classes{" +
                    "innerClassInfoIndex=" + innerClassInfoIndex +
                    ", outerClassInfoIndex=" + outerClassInfoIndex +
                    ", innerNameInex=" + innerNameInex + " -> " + ((UTF8) BytecodeParser.constantItemHashMap.get(innerNameInex)).value +
                    ", innerClassAccessFlags=" + innerClassAccessFlags + " -> " + AccessFlags.printAccess(innerClassAccessFlags) +
                    '}';
        }
    }

    int numberOfClasses; //u2
    private Classes[] mClasses;

    @Override
    protected int contentSize() {
        return numberOfClasses * Classes.size + 2;
    }

    @Override
    public void parseInner(byte[] bytes, int offset) {
        numberOfClasses = Utils.read2Number(bytes, offset);
        offset += 2;
        mClasses = new Classes[numberOfClasses];
        for (int i = 0; i < numberOfClasses; i++) {
            mClasses[i] = new Classes();
            mClasses[i].parse(bytes, offset);
            offset += Classes.size;
        }
    }

    @Override
    public String toString() {
        return "InnerClasses{" +
                "numberOfClasses=" + numberOfClasses +
                ", mClasses=" + Arrays.toString(mClasses) +
                '}';
    }
}

泛型签名属性

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39


/**
 * <pre>
 * Signature_attribute {
 *     u2 attribute_name_index;
 *     u4 attribute_length;
 *     u2 signature_index;
 * }
 * </pre>
 */
class Signature extends Info {

    int signatureIndex; //u2

    @Override
    protected int contentSize() {
        return 2;
    }

    @Override
    public void parseInner(byte[] bytes, int offset) {
        signatureIndex = Utils.read2Number(bytes, offset);
    }

    @Override
    public String toString() {
        ConstantItem constantItem = BytecodeParser.constantItemHashMap.get(signatureIndex);
        String signature = constantItem.toString();
        if (constantItem instanceof UTF8) {
            signature = ((UTF8) constantItem).value;
        } else if (constantItem instanceof METHOD_REF) {
            signature = constantItem.toString();
        } else if (constantItem instanceof STRING) {
            signature = ((UTF8) BytecodeParser.constantItemHashMap.get(((STRING) constantItem).index)).value;
        }
        return "Signature{" +
                "signatureIndex=" + signatureIndex + " -> " + signature +
                '}';
    }
}

StackMapTable 属性

StackMapTable 用于优化类型检查效率的。https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html#jvms-4.7.4

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76


/**
 * https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html#jvms-4.7.4
 * <pre>
 * StackMapTable_attribute {
 *     u2              attribute_name_index;
 *     u4              attribute_length;
 *     u2              number_of_entries;
 *     stack_map_frame entries[number_of_entries];
 * }
 *
 * union stack_map_frame {
 *     same_frame;
 *     same_locals_1_stack_item_frame;
 *     same_locals_1_stack_item_frame_extended;
 *     chop_frame;
 *     same_frame_extended;
 *     append_frame;
 *     full_frame;
 * }
 * </pre>
 */
class StackMapTable extends Info {

    class StackMapFrame {
        /**
         * <pre>
         * same_frame {
         *     u1 frame_type = SAME; // 0-63
         * }
         * </pre>
         */
        class SameFrame {
            int frame_type; //u1
        }

        /**
         * <pre>
         * same_locals_1_stack_item_frame {
         *     u1 frame_type = SAME_LOCALS_1_STACK_ITEM; // 64-127
         *     verification_type_info stack[1];
         * }
         * </pre>
         */
        class SameLocals1StackItemFrame {
        }

        class SameLocals1StackItemFrameExtended {
        }

        class ChopFrame {
        }

        class SameFrameExtended {
        }

        class AppendFrame {
        }

        class FullFrame {
        }
    }

    int numberOfEntries; //u2

    private StackMapFrame[] mStackMapFrames;

    @Override
    protected int contentSize() {
        return 0;
    }

    @Override
    public void parseInner(byte[] bytes, int offset) {

    }
}

Synthetic 编译器合成属性

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20


/**
 * <pre>
 * Synthetic_attribute {
 *     u2 attribute_name_index;
 *     u4 attribute_length; //always zero
 * }
 * </pre>
 */
class Synthetic extends Info {

    @Override
    protected int contentSize() {
        return 0;
    }

    @Override
    public void parseInner(byte[] bytes, int offset) {

    }
}

Deprecated 属性

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19


/**
 * <pre>
 * Deprecated_attribute {
 *     u2 attribute_name_index;
 *     u4 attribute_length;
 * }
 * </pre>
 */
class Deprecated extends Info {
    @Override
    protected int contentSize() {
        return 0;
    }

    @Override
    public void parseInner(byte[] bytes, int offset) {

    }
}

LocalVariableTypeTable

局部变量类型属性

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77


/**
 * <pre>
 *  LocalVariableTypeTable_attribute {
 *     u2 attribute_name_index;
 *     u4 attribute_length;
 *     u2 local_variable_type_table_length;
 *     {   u2 start_pc;
 *         u2 length;
 *         u2 name_index;
 *         u2 signature_index;
 *         u2 index;
 *     } local_variable_type_table[local_variable_type_table_length];
 * }
 * </pre>
 */
class LocalVariableTypeTable extends Info {

    class Local_variable_type_table implements Parsable {
        int start_pc;
        int length;
        int name_index;
        int signature_index;
        int index;

        public static final int size = 10;

        @Override
        public void parse(byte[] bytes, int offset) {
            start_pc = Utils.read2Number(bytes, offset);
            length = Utils.read2Number(bytes, offset + 2);
            name_index = Utils.read2Number(bytes, offset + 4);
            signature_index = Utils.read2Number(bytes, offset + 6);
            index = Utils.read2Number(bytes, offset + 8);
        }

        @Override
        public String toString() {
            return "Local_variable_type_table{" +
                    "start_pc=" + start_pc +
                    ", length=" + length +
                    ", name_index=" + name_index +
                    ", signature_index=" + signature_index +
                    ", index=" + index +
                    '}';
        }
    }

    int lvtt_length; //u2
    Local_variable_type_table[] mTables;

    @Override
    protected int contentSize() {
        return lvtt_length * Local_variable_type_table.size + 2;
    }

    @Override
    public void parseInner(byte[] bytes, int offset) {
        lvtt_length = Utils.read2Number(bytes, offset);
        offset += 2;
        mTables = new Local_variable_type_table[lvtt_length];
        for (int i = 0; i < lvtt_length; i++) {
            mTables[i] = new Local_variable_type_table();
            mTables[i].parse(bytes, offset);
            offset += Local_variable_type_table.size;
        }
    }

    @Override
    public String toString() {
        return "LocalVariableTypeTable{" +
                "lvtt_length=" + lvtt_length +
                ", mTables=" + Arrays.toString(mTables) +
                '}';
    }
}

//endregion

数值处理的工具类

由于 Java 的所有数字类型都是 signed 类型，就会导致 unsigned 的数到了 Java 中可能越界溢出。所以统一使用 Java 的 int 代表 unsigned byte。

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34


class Utils {
    /**
     * 获取占4字节的数
     */
    static int read4Number(byte[] bytes, int offset) {
        return ((bytes[offset] & 0xFF) << 24) | ((bytes[offset + 1] & 0xFF) << 16) | ((bytes[offset + 2] & 0xFF) << 8) | ((bytes[offset + 3] & 0xFF));
    }

    /**
     * 获取占2字节的数, 为了避免 java 中只有 signed short 越界出现显示了负数, 所以返回 int
     */
    static int read2Number(byte[] bytes, int offset) {
        return ((bytes[offset] & 0xFF) << 8) | (bytes[offset + 1] & 0xFF);
    }

    static int readUnsignedByte(byte[] bytes, int offset) {
        return (bytes[offset] & 0xFF);
    }

    /**
     * 获得占8字节的数
     */
    static long read8Number(byte[] bytes, int offset) {
        return (
                ((long) bytes[offset] & 0xFF) << 56) |
                (((long) bytes[offset + 1] & 0xFF) << 48) |
                (((long) bytes[offset + 2] & 0xFF) << 40) |
                (((long) bytes[offset + 3] & 0xFF) << 32) |
                (((long) bytes[offset + 3] & 0xFF) << 24) |
                (((long) bytes[offset + 3] & 0xFF) << 16) |
                (((long) bytes[offset + 3] & 0xFF) << 8) |
                (((long) bytes[offset + 3] & 0xFF));
    }
}