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ASM4.0源码走读之一

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       了解java class文件格式是读懂asm代码的前提,所以在此之前请找Java虚拟机规范里边class文件格式章节细读一下。

        不过在详解读入过程之前,先简单看下jvm规范中对class文件格式的定义,其中一个u代表一个byte,u1、u2、u4分别代表1、2、4个字节:

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]; 
}

        我们用一个简单的例子作为切入点:用 ClassReader读入class文件内容,构造一个ClassNode的过程:

    public static void main(String[] args) throws IOException {
        ClassReader cr = new ClassReader("com.tmall.buy.FullClass");//ClassReader只是按顺序遍历一遍class文件内容,基本不做信息的缓存,类似于
        ClassNode cn = new ClassNode();//ClassNode是会缓存下class相关的信息的,类似于dom方法访问xml
        cr.accept(cn, ClassReader.EXPAND_FRAMES);
        System.out.println(cn.name);
    }

         其中

 ClassReader("com.tmall.buy.FullClass"),
         会读入class文件;其实现:
 readClass(ClassLoader.getSystemResourceAsStream(name.replace('.', '/') + ".class"), true)
        读入过程是用的bootstrap class loader或者system class loader装载class,然后getResource的。读入的是class文件的字节数组,然后调用ClassReader的另外一个构造函数: 
   public ClassReader(final byte[] b) 
   -->
   public ClassReader(final byte[] b, final int off, final int len) 
 来看下这个构造函数的实现:
    public ClassReader(final byte[] b, final int off, final int len) {
        this.b = b;
        // checks the class version
        if (readShort(off + 6) > Opcodes.V1_8) {//检查主版本号,major_version,此处Opcodes.V1_8是52,即1.8
            throw new IllegalArgumentException();
        }
        // parses the constant pool
        items = new int[readUnsignedShort(off + 8)];//读取常量池数量,constant_pool_count
        int n = items.length;
        strings = new String[n];
        int max = 0;
        int index = off + 10;
        for (int i = 1; i < n; ++i) {//读取常量池数组内容
            items[i] = index + 1;//保存常量池内容在class内容字节数组的开始位置,后续用到某个常量池时,可以直接从class文件字节数组中读
            int size;
            switch (b[index]) {//不同tag类型的常量池占用的字节长度不同,详见jvm spec
            case ClassWriter.FIELD:
            case ClassWriter.METH:
            case ClassWriter.IMETH:
            case ClassWriter.INT:
            case ClassWriter.FLOAT:
            case ClassWriter.NAME_TYPE:
            case ClassWriter.INDY:
                size = 5;
                break;
            case ClassWriter.LONG:
            case ClassWriter.DOUBLE:
                size = 9;
                ++i;
                break;
            case ClassWriter.UTF8:
                size = 3 + readUnsignedShort(index + 1);
                if (size > max) {
                    max = size;
                }
                break;
            case ClassWriter.HANDLE:
                size = 4;
                break;
            // case ClassWriter.CLASS:
            // case ClassWriter.STR:
            // case ClassWriter.MTYPE
            default:
                size = 3;
                break;
            }
            index += size;
        }
        maxStringLength = max;//记录下了utf8常量池中最长字符串的长度
        // the class header information starts just after the constant pool
        header = index;//把到常量池结尾为止的字节长度作为了header的长度
    }
        这里并没有解析出常量池数组,只是记录了class文件header的长度。此处header包括魔数、主次版本号、常量池数量、每个常量池在class文件字节码数组中的起始字节位置。接下来就是access_flags、this_class、super_class了。
        ClassReader.accept(final byte[] b)调用了同名accept不同参的accept方法:
   public void accept(final ClassVisitor classVisitor,
            final Attribute[] attrs, final int flags) {
        int u = header; // current offset in the class file
        char[] c = newchar[maxStringLength]; // buffer used to read strings 还记得这个maxStringLength吧
        Context context = new Context();
        context.attrs = attrs;
        context.flags = flags;
        context.buffer = c;
        // reads the class declaration
        int access = readUnsignedShort(u);//class的访问标示符
        String name = readClass(u + 2, c);//读取class name,是从常量池读取的utf8字符串;从items数组读取到常量池字节内容的起始位置,读取具体内容,并缓存到strings数组中,后续如果多次读到会从缓存取
        String superClass = readClass(u + 4, c);//读取超类class name
        String[] interfaces = new String[readUnsignedShort(u + 6)];//读取实现的接口数量
        u += 8;
        for (int i = 0; i < interfaces.length; ++i) {
            interfaces[i] = readClass(u, c);//读取接口name
            u += 2;
        }
        // reads the class attributes
        String signature = null;
        String sourceFile = null;
        String sourceDebug = null;
        String enclosingOwner = null;
        String enclosingName = null;
        String enclosingDesc = null;
        int anns = 0;
        int ianns = 0;
        int tanns = 0;
        int itanns = 0;
        int innerClasses = 0;
        Attribute attributes = null;


        u = getAttributes();//计算属性开始的位置,计算的时候是跳过了字段和方法相关信息
        for (int i = readUnsignedShort(u); i > 0; --i) {
            String attrName = readUTF8(u + 2, c);//从常量池读取属性名称
            // tests are sorted in decreasing frequency order
            // (based on frequencies observed on typical classes)
            if ("SourceFile".equals(attrName)) {
                sourceFile = readUTF8(u + 8, c);//源文件文件名
            } else if ("InnerClasses".equals(attrName)) {
                innerClasses = u + 8;//内部类数量
            } else if ("EnclosingMethod".equals(attrName)) {
                enclosingOwner = readClass(u + 8, c);
                int item = readUnsignedShort(u + 10);
                if (item != 0) {
                    enclosingName = readUTF8(items[item], c);
                    enclosingDesc = readUTF8(items[item] + 2, c);
                }
            } else if (SIGNATURES && "Signature".equals(attrName)) {//类型、属性等泛型相关
                signature = readUTF8(u + 8, c);
            } else if (ANNOTATIONS
                    && "RuntimeVisibleAnnotations".equals(attrName)) {
                anns = u + 8;
            } else if (ANNOTATIONS
                    && "RuntimeVisibleTypeAnnotations".equals(attrName)) {
                tanns = u + 8;
            } else if ("Deprecated".equals(attrName)) {
                access |= Opcodes.ACC_DEPRECATED;
            } else if ("Synthetic".equals(attrName)) {
                access |= Opcodes.ACC_SYNTHETIC
                        | ClassWriter.ACC_SYNTHETIC_ATTRIBUTE;
            } else if ("SourceDebugExtension".equals(attrName)) {//扩展调试信息,对jvm来说没有实际的语义
                int len = readInt(u + 4);
                sourceDebug = readUTF(u + 8, len, new char[len]);
            } else if (ANNOTATIONS
                    && "RuntimeInvisibleAnnotations".equals(attrName)) {
                ianns = u + 8;
            } else if (ANNOTATIONS
                    && "RuntimeInvisibleTypeAnnotations".equals(attrName)) {
                itanns = u + 8;
            } else if ("BootstrapMethods".equals(attrName)) {
                int[] bootstrapMethods = new int[readUnsignedShort(u + 8)];
                for (int j = 0, v = u + 10; j < bootstrapMethods.length; j++) {
                    bootstrapMethods[j] = v;
                    v += 2 + readUnsignedShort(v + 2) << 1;
                }
                context.bootstrapMethods = bootstrapMethods;
            } else {
                Attribute attr = readAttribute(attrs, attrName, u + 8,
                        readInt(u + 4), c, -1, null);
                if (attr != null) {
                    attr.next = attributes;
                    attributes = attr;
                }
            }
            u += 6 + readInt(u + 4);
        }


        // visits the class declaration 这里这个classVisitor是ClassNode实力,visit方法会记录下传入的参数信息
        classVisitor.visit(readInt(items[1] - 7), access, name, signature,
                superClass, interfaces);


        // visits the source and debug info
        if ((flags & SKIP_DEBUG) == 0
                && (sourceFile != null || sourceDebug != null)) {
            classVisitor.visitSource(sourceFile, sourceDebug);
        }


        // visits the outer class
        if (enclosingOwner != null) {
            classVisitor.visitOuterClass(enclosingOwner, enclosingName,
                    enclosingDesc);
        }


        // visits the class annotations and type annotations
        if (ANNOTATIONS && anns != 0) {//Runtime Visible Annotation,什么时候会出现咧?
            for (int i = readUnsignedShort(anns), v = anns + 2; i > 0; --i) {
                v = readAnnotationValues(v + 2, c, true,
                        classVisitor.visitAnnotation(readUTF8(v, c), true));//记录annotation
            }
        }
        if (ANNOTATIONS && ianns != 0) {//Runtime Invisible Annotation
            for (int i = readUnsignedShort(ianns), v = ianns + 2; i > 0; --i) {
                v = readAnnotationValues(v + 2, c, true,
                        classVisitor.visitAnnotation(readUTF8(v, c), false));
            }
        }
        if (ANNOTATIONS && tanns != 0) {//Runtime Visible Type Annotation
            for (int i = readUnsignedShort(tanns), v = tanns + 2; i > 0; --i) {
                v = readAnnotationTarget(context, v);
                v = readAnnotationValues(v + 2, c, true,
                        classVisitor.visitTypeAnnotation(context.target,
                                context.path, readUTF8(v, c), true));
            }
        }
        if (ANNOTATIONS && itanns != 0) {//Runtime Invisible Type Annotation
            for (int i = readUnsignedShort(itanns), v = itanns + 2; i > 0; --i) {
                v = readAnnotationTarget(context, v);
                v = readAnnotationValues(v + 2, c, true,
                        classVisitor.visitTypeAnnotation(context.target,
                                context.path, readUTF8(v, c), false));
            }
        }


        // visits the attributes
        while (attributes != null) {
            Attribute attr = attributes.next;
            attributes.next = null;
            classVisitor.visitAttribute(attributes);//类非标准attributes
            attributes = attr;
        }


        // visits the inner classes
        if (innerClasses != 0) {
            int v = innerClasses + 2;
            for (int i = readUnsignedShort(innerClasses); i > 0; --i) {
                classVisitor.visitInnerClass(readClass(v, c),
                        readClass(v + 2, c), readUTF8(v + 4, c),
                        readUnsignedShort(v + 6));//记录下内部类信息
                v += 8;
            }
        }


        // visits the fields and methods 此时u指向了field count结束的位置
        u = header + 10 + 2 * interfaces.length;
        for (int i = readUnsignedShort(u - 2); i > 0; --i) {//读取field count
            u = readField(classVisitor, context, u);//读取field
        }
        u += 2;//跳过method count所在位置
        for (int i = readUnsignedShort(u - 2); i > 0; --i) {//读取method count
            u = readMethod(classVisitor, context, u);
        }


        // visits the end of the class
        classVisitor.visitEnd();
    }
         来看跳过字段和方法,拿到属性开始位置的实现:
    private int getAttributes() {
        // skips the header 此时header是跳过magic number、minor version、major version、constant_pool_count、constant_pool[constant_pool_count - 1]之后的位置;这里+8是跳过当前类的access flag(u2)、class name(u2)、super class name(u2)、interface count(u2);readUnsignedShort(header + 6)就是读取interface count,* 2是所有interfaces占用的字节数
        int u = header + 8 + readUnsignedShort(header + 6) * 2;
        // skips fields and methods 现在u是从filed_count开始的
        for (int i = readUnsignedShort(u); i > 0; --i) {//i初始化为filed_count的值
            for (int j = readUnsignedShort(u + 8); j > 0; --j) {//u + 8位置开始的unsigned short是指field的attributes count(u2);8包括field_count(u2)、filed的access flag(u2)、name_index(u2)、descriptor_index(u2)
                u += 6 + readInt(u + 12);//6是指attribute的前六个字节,attribute_name_index(u2)、attribute_length(u4);u+12开始这个int是attribute_length,此处12是初始化j处用到的8 + attributes_count(u2) + attribute_name_index(u2);注意这里只u += 6 + attributes info长度,即属性本身的长度,字段内容占的8个字节和field count(u2)没有算在内
            }
            u += 8;//可以理解为field占用的8个字节,包括access_flag(u2)、name_index(u2)、descriptor_index(u2)、attributes_count(u2)
        }
        u += 2;//可以理解为field_count(u2)占用的长度
        for (int i = readUnsignedShort(u); i > 0; --i) {//读取方法内容的方式跟读取字段的方式一致;外层循环u+=8和循环后u+=2有时候容易搞不清楚的
            for (int j = readUnsignedShort(u + 8); j > 0; --j) {
                u += 6 + readInt(u + 12);
            }
            u += 8;
        }
        // the attribute_info structure starts just after the methods
        return u + 2;
    }
         ClassReader中的classVisitor实例字段是ClassNode对象,根据ClassReader.accept方法中ClassNode方法出现的顺序来一个个看下:
   /**
     *记录下版本号、访问表示符、类名称、类型泛型信息、超类、接口信息
     */
    public void visit(final int version, final int access, final String name,
            final String signature, final String superName,
            final String[] interfaces) {
        this.version = version;
        this.access = access;
        this.name = name;
        this.signature = signature;
        this.superName = superName;
        if (interfaces != null) {
            this.interfaces.addAll(Arrays.asList(interfaces));
        }
    }
    /**
     * 记录下sourceFile我sourceDebug信息
     */
    public void visitSource(final String file, final String debug) {
        sourceFile = file;
        sourceDebug = debug;
    }
 ……其他方法比较简单,忽略。来看看readField的实现:
    private int readField(final ClassVisitor classVisitor,
            final Context context, int u) {
        // reads the field declaration
        char[] c = context.buffer;
        int access = readUnsignedShort(u);//field access
        String name = readUTF8(u + 2, c);//field name
        String desc = readUTF8(u + 4, c);//descriptor
        u += 6;


        // reads the field attributes
        String signature = null;
        int anns = 0;
        int ianns = 0;
        int tanns = 0;
        int itanns = 0;
        Object value = null;
        Attribute attributes = null;


        for (int i = readUnsignedShort(u); i > 0; --i) {//field的属性
            String attrName = readUTF8(u + 2, c);//属性名
            // tests are sorted in decreasing frequency order
            // (based on frequencies observed on typical classes)
            if ("ConstantValue".equals(attrName)) {
                int item = readUnsignedShort(u + 8);
                value = item == 0 ? null : readConst(item, c);
            } else if (SIGNATURES && "Signature".equals(attrName)) {
                signature = readUTF8(u + 8, c);
            } else if ("Deprecated".equals(attrName)) {
                access |= Opcodes.ACC_DEPRECATED;
            } else if ("Synthetic".equals(attrName)) {
                access |= Opcodes.ACC_SYNTHETIC
                        | ClassWriter.ACC_SYNTHETIC_ATTRIBUTE;
            } else if (ANNOTATIONS
                    && "RuntimeVisibleAnnotations".equals(attrName)) {
                anns = u + 8;
            } else if (ANNOTATIONS
                    && "RuntimeVisibleTypeAnnotations".equals(attrName)) {
                tanns = u + 8;
            } else if (ANNOTATIONS
                    && "RuntimeInvisibleAnnotations".equals(attrName)) {
                ianns = u + 8;
            } else if (ANNOTATIONS
                    && "RuntimeInvisibleTypeAnnotations".equals(attrName)) {
                itanns = u + 8;
            } else {//非标准的属性
                Attribute attr = readAttribute(context.attrs, attrName, u + 8,
                        readInt(u + 4), c, -1, null);
                if (attr != null) {
                    attr.next = attributes;
                    attributes = attr;
                }
            }
            u += 6 + readInt(u + 4);//6表示 attribute_name_index(u2)、attribute_length(u4),没计算attribute count(u2)的
        }
        u += 2;//attribute count(u2)


        // visits the field declaration
        FieldVisitor fv = classVisitor.visitField(access, name, desc,
                signature, value);//给ClassNode添加一个FieldNode;后续会给FieldNode添加attribute
        if (fv == null) {
            return u;
        }


        // visits the field annotations and type annotations
        if (ANNOTATIONS && anns != 0) {
            for (int i = readUnsignedShort(anns), v = anns + 2; i > 0; --i) {
                v = readAnnotationValues(v + 2, c, true,
                        fv.visitAnnotation(readUTF8(v, c), true));
            }
        }
        if (ANNOTATIONS && ianns != 0) {
            for (int i = readUnsignedShort(ianns), v = ianns + 2; i > 0; --i) {
                v = readAnnotationValues(v + 2, c, true,
                        fv.visitAnnotation(readUTF8(v, c), false));
            }
        }
        if (ANNOTATIONS && tanns != 0) {
            for (int i = readUnsignedShort(tanns), v = tanns + 2; i > 0; --i) {
                v = readAnnotationTarget(context, v);
                v = readAnnotationValues(v + 2, c, true,
                        fv.visitTypeAnnotation(context.target, context.path,
                                readUTF8(v, c), true));
            }
        }
        if (ANNOTATIONS && itanns != 0) {
            for (int i = readUnsignedShort(itanns), v = itanns + 2; i > 0; --i) {
                v = readAnnotationTarget(context, v);
                v = readAnnotationValues(v + 2, c, true,
                        fv.visitTypeAnnotation(context.target, context.path,
                                readUTF8(v, c), false));
            }
        }


        // visits the field attributes
        while (attributes != null) {
            Attribute attr = attributes.next;
            attributes.next = null;
            fv.visitAttribute(attributes);
            attributes = attr;
        }


        // visits the end of the field
        fv.visitEnd();


        return u;
    }

    
         readMethod实现,跟readField很像,读取方法访问标示、方法名、描述符、属性等,最重要的在最后readCode,读取方法体字节码内容:
private int readMethod(final ClassVisitor classVisitor,
            final Context context, int u) {
        // reads the method declaration
        char[] c = context.buffer;
        // 节操碎了一地的context君,每次readMethod的时候都会缓存当前方法的access、name、desc等信息,后续使用;使用完后下次就被覆盖了
        context.access = readUnsignedShort(u);//access flag
        context.name = readUTF8(u + 2, c);//方法名
        context.desc = readUTF8(u + 4, c);//方法描述符
        u += 6;


        // reads the method attributes
        int code = 0;
        int exception = 0;
        String[] exceptions = null;
        String signature = null;
        int anns = 0;
        int ianns = 0;
        int tanns = 0;
        int itanns = 0;
        int dann = 0;
        int mpanns = 0;
        int impanns = 0;
        int firstAttribute = u;
        Attribute attributes = null;


        for (int i = readUnsignedShort(u); i > 0; --i) {
            String attrName = readUTF8(u + 2, c);
            // tests are sorted in decreasing frequency order
            // (based on frequencies observed on typical classes)
            if ("Code".equals(attrName)) {
                if ((context.flags & SKIP_CODE) == 0) {
                    code = u + 8;
                }
            } else if ("Exceptions".equals(attrName)) {
                exceptions = new String[readUnsignedShort(u + 8)];
                exception = u + 10;
                for (int j = 0; j < exceptions.length; ++j) {
                    exceptions[j] = readClass(exception, c);
                    exception += 2;
                }
            } else if (SIGNATURES && "Signature".equals(attrName)) {
                signature = readUTF8(u + 8, c);
            } else if ("Deprecated".equals(attrName)) {
                context.access |= Opcodes.ACC_DEPRECATED;
            } else if (ANNOTATIONS
                    && "RuntimeVisibleAnnotations".equals(attrName)) {
                anns = u + 8;
            } else if (ANNOTATIONS
                    && "RuntimeVisibleTypeAnnotations".equals(attrName)) {
                tanns = u + 8;
            } else if (ANNOTATIONS && "AnnotationDefault".equals(attrName)) {
                dann = u + 8;
            } else if ("Synthetic".equals(attrName)) {
                context.access |= Opcodes.ACC_SYNTHETIC
                        | ClassWriter.ACC_SYNTHETIC_ATTRIBUTE;
            } else if (ANNOTATIONS
                    && "RuntimeInvisibleAnnotations".equals(attrName)) {
                ianns = u + 8;
            } else if (ANNOTATIONS
                    && "RuntimeInvisibleTypeAnnotations".equals(attrName)) {
                itanns = u + 8;
            } else if (ANNOTATIONS
                    && "RuntimeVisibleParameterAnnotations".equals(attrName)) {
                mpanns = u + 8;
            } else if (ANNOTATIONS
                    && "RuntimeInvisibleParameterAnnotations".equals(attrName)) {
                impanns = u + 8;
            } else {
                Attribute attr = readAttribute(context.attrs, attrName, u + 8,
                        readInt(u + 4), c, -1, null);
                if (attr != null) {
                    attr.next = attributes;
                    attributes = attr;
                }
            }
            u += 6 + readInt(u + 4);
        }
        u += 2;


        // visits the method declaration
        MethodVisitor mv = classVisitor.visitMethod(context.access,
                context.name, context.desc, signature, exceptions);//ClassNode会创建并记录一个MethodNode对象
        if (mv == null) {
            return u;
        }


        /*
         * if the returned MethodVisitor is in fact a MethodWriter, it means
         * there is no method adapter between the reader and the writer. If, in
         * addition, the writer's constant pool was copied from this reader
         * (mw.cw.cr == this), and the signature and exceptions of the method
         * have not been changed, then it is possible to skip all visit events
         * and just copy the original code of the method to the writer (the
         * access, name and descriptor can have been changed, this is not
         * important since they are not copied as is from the reader).
         */
        if (WRITER && mv instanceof MethodWriter) {
            MethodWriter mw = (MethodWriter) mv;
            if (mw.cw.cr == this && signature == mw.signature) {
                boolean sameExceptions = false;
                if (exceptions == null) {
                    sameExceptions = mw.exceptionCount == 0;
                } else if (exceptions.length == mw.exceptionCount) {
                    sameExceptions = true;
                    for (int j = exceptions.length - 1; j >= 0; --j) {
                        exception -= 2;
                        if (mw.exceptions[j] != readUnsignedShort(exception)) {
                            sameExceptions = false;
                            break;
                        }
                    }
                }
                if (sameExceptions) {
                    /*
                     * we do not copy directly the code into MethodWriter to
                     * save a byte array copy operation. The real copy will be
                     * done in ClassWriter.toByteArray().
                     */
                    mw.classReaderOffset = firstAttribute;
                    mw.classReaderLength = u - firstAttribute;
                    return u;
                }
            }
        }


        // visits the method annotations
        if (ANNOTATIONS && dann != 0) {
            AnnotationVisitor dv = mv.visitAnnotationDefault();
            readAnnotationValue(dann, c, null, dv);
            if (dv != null) {
                dv.visitEnd();
            }
        }
        if (ANNOTATIONS && anns != 0) {
            for (int i = readUnsignedShort(anns), v = anns + 2; i > 0; --i) {
                v = readAnnotationValues(v + 2, c, true,
                        mv.visitAnnotation(readUTF8(v, c), true));
            }
        }
        if (ANNOTATIONS && ianns != 0) {
            for (int i = readUnsignedShort(ianns), v = ianns + 2; i > 0; --i) {
                v = readAnnotationValues(v + 2, c, true,
                        mv.visitAnnotation(readUTF8(v, c), false));
            }
        }
        if (ANNOTATIONS && tanns != 0) {
            for (int i = readUnsignedShort(tanns), v = tanns + 2; i > 0; --i) {
                v = readAnnotationTarget(context, v);
                v = readAnnotationValues(v + 2, c, true,
                        mv.visitTypeAnnotation(context.target, context.path,
                                readUTF8(v, c), true));
            }
        }
        if (ANNOTATIONS && itanns != 0) {
            for (int i = readUnsignedShort(itanns), v = itanns + 2; i > 0; --i) {
                v = readAnnotationTarget(context, v);
                v = readAnnotationValues(v + 2, c, true,
                        mv.visitTypeAnnotation(context.target, context.path,
                                readUTF8(v, c), false));
            }
        }
        if (ANNOTATIONS && mpanns != 0) {
            readParameterAnnotations(mv, context, mpanns, true);
        }
        if (ANNOTATIONS && impanns != 0) {
            readParameterAnnotations(mv, context, impanns, false);
        }


        // visits the method attributes
        while (attributes != null) {
            Attribute attr = attributes.next;
            attributes.next = null;
            mv.visitAttribute(attributes);
            attributes = attr;
        }


        // visits the method code
        if (code != 0) {
            mv.visitCode();
            readCode(mv, context, code);//解析字节码,最重要的地方
        }


        // visits the end of the method
        mv.visitEnd();


        return u;
    }
         MethodNode会记录方法相关的信息,同时会初始化存储local variables、tryCatch、exception、instruction的数据结构
    public MethodNode(final int api, final int access, final String name,
            final String desc, final String signature, final String[] exceptions) {
        super(api);
        this.access = access;
        this.name = name;
        this.desc = desc;
        this.signature = signature;
        this.exceptions = new ArrayList<String>(exceptions == null ? 0
                : exceptions.length);
        boolean isAbstract = (access & Opcodes.ACC_ABSTRACT) != 0;
        if (!isAbstract) {
            this.localVariables = new ArrayList<LocalVariableNode>(5);
        }
        this.tryCatchBlocks = new ArrayList<TryCatchBlockNode>();
        if (exceptions != null) {
            this.exceptions.addAll(Arrays.asList(exceptions));
        }
        this.instructions = new InsnList();
    }

 最最重要的readCode的实现我们下篇分析。

 

《未完待续》

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