使用ASM对JAVA class file进行修改的技术 -- 添加类方法

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我是靠谱客的博主谦让大门，最近开发中收集的这篇文章主要介绍使用ASM对JAVA class file进行修改的技术 -- 添加类方法，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

使用ASM包进行Class File修改真是很方便，不过可惜的是ASM不提供现成的方法修改工具，那我们就利用它提供的强大的字节码操作能力，自己来做一个吧：

基本思路如下：假设操作类为A, 假设要加的方法为MA,我们为了操作上方便,构造类B,将类B的MA方法加到A上就可以了，有了这个思路即可快速实现如下代码：

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首先构造Visitor用于添加方法MA:

public class BytecodeClassMethodAdder extends ClassAdapter {

// method nodes for appending operation
private final List<MethodNode> methodNodesToAppend;

/**
* Construction for bytecode class method adder operation
*
* @param cv
* @param methodNodes
*/
public BytecodeClassMethodAdder(final ClassVisitor cv, List<MethodNode> methodNodes) {
  super(cv);

  // all method nodes needed to append for current class
  this.methodNodesToAppend = methodNodes;
}

/**
* visit end of this adapter for current class
*
*/
@SuppressWarnings("unchecked")
public void visitEnd() {
  for (MethodNode mn : this.methodNodesToAppend) {
   List exceptions = mn.exceptions;
   String [] earray = null;
   if (exceptions.size() > 0){
    earray = new String[exceptions.size()];
    for (int i=0; i<exceptions.size(); i++){
     String exception = (String)exceptions.get(i);
     earray[i] = exception;
    }
   }
   mn.accept(cv);    //add this method node to the visitor operation
  }

  // overload the visiting operation
  super.visitEnd();
}

}

-----------------------------------------------------------------------------------------------------------

然后构造从另外一个类B中抽取方法的操作类：

public class BytecodeClassFilterUtil implements IBytecodeContainer{

private ClassNode classNode = null;

/**
* bytecode class filter utility construction
*
* @param classFile
* @param op
* @throws IOException
*/
public BytecodeClassFilterUtil(final String classFile) throws IOException {
FileInputStream fis = new FileInputStream(classFile);
ClassReader cr = new ClassReader(fis);
BytecodeClassFilter ca = new BytecodeClassFilter(null);
cr.accept(ca, ClassReader.EXPAND_FRAMES);
if (fis != null) {
   fis.close();
}
}

/**
* bytecode class filter utility construction
*
* @param classFile
* @param op
* @throws IOException
*/
public BytecodeClassFilterUtil(File classFile) throws IOException {
FileInputStream fis = new FileInputStream(classFile);
ClassReader cr = new ClassReader(fis);
BytecodeClassFilter ca = new BytecodeClassFilter(null);
cr.accept(ca, ClassReader.EXPAND_FRAMES);
if (fis != null) {
   fis.close();
}
}

/**
* get a specified class node instance for current bytecode class filter utility
*
* @return
*/
public ClassNode getClassNode() {
return this.classNode;
}

/**
* get a specified field node by a specified name pattern and description pattern
*
* @param name
* @return
*/
@SuppressWarnings("unchecked")
public List<FieldNode> getFieldNode(String namePattern, String descPattern) {
List<FieldNode> returnNodes = new ArrayList<FieldNode>();
List fields = this.classNode.fields;
if (fields != null) {
   for (Object ofield : fields) {
    FieldNode field = (FieldNode) ofield;
    boolean blnNameMatch = true;
    boolean blnDescMatch = true;
    if (namePattern != null) {
     blnNameMatch = Pattern.matches(namePattern, field.name);
    }
    if (descPattern != null) {
     blnDescMatch = Pattern.matches(descPattern, field.desc);
    }
    if (blnNameMatch && blnDescMatch) {
     returnNodes.add(field);
    }
   }
}
return returnNodes;
}

/**
* get a specified method name or a list of them.
*
* @param name
* @param description
* @return
*/
@SuppressWarnings("unchecked")
public List<MethodNode> getMethodNode(String namePattern, String descPattern) {
List<MethodNode> returnNodes = new ArrayList<MethodNode>();
List methods = this.classNode.methods;
if (methods != null) {
   for (Object omethod : methods) {
    MethodNode method = (MethodNode) omethod;
    boolean blnNameMatch = true;
    boolean blnDescMatch = true;
    if (namePattern != null) {
     blnNameMatch = Pattern.matches(namePattern, method.name);
    }
    if (descPattern != null) {
     blnDescMatch = Pattern.matches(descPattern, method.desc);
    }
    if (blnNameMatch && blnDescMatch) {
     returnNodes.add(method);
    }
   }
}
return returnNodes;
}

/**
* get all of the field descriptions for a specified class
*
* @return
*/
@SuppressWarnings("unchecked")
public List<String> getFieldDescription() {
List<String> descList = new ArrayList<String>();
List fields = this.classNode.fields;
if (fields != null) {
   for (Object ofield : fields) {
    FieldNode field = (FieldNode) ofield;
    StringBuilder sb = new StringBuilder();
    sb.append(field.name).append(":").append(field.desc);
    descList.add(sb.toString());
   }
}
return descList;
}

/**
* get all of the method list for a specified class
*
* @return
*/
@SuppressWarnings("unchecked")
public List<String> getMethodDescription() {
List<String> descList = new ArrayList<String>();
List methods = this.classNode.methods;
if (methods != null) {
   for (Object omethod : methods) {
    MethodNode method = (MethodNode) omethod;
    StringBuilder sb = new StringBuilder();
    sb.append(method.name).append(":").append(method.desc);
    descList.add(sb.toString());
   }
}
return descList;
}

/**
* bytecode class filter extend from class adpater class.
*
*/
class BytecodeClassFilter extends ClassAdapter {

// construction call for current class
public BytecodeClassFilter(final ClassVisitor cv) {
   super(new ClassNode() {
    public void visitEnd() {
     if (cv != null) {
      accept(cv);
     }
    }
   });
}

// execute the next operation after this visit ending
public void visitEnd() {
classNode = (ClassNode) cv;
}

}

------------------------------------------------------------------------------------------------

构造调用函数，实现方法“转移”功能:

public void addMethodToClass(String src, String des, String combine, String nameFilter, String descFilter)
   throws IOException {
  BytecodeClassFilterUtil util = new BytecodeClassFilterUtil(src);
  List<MethodNode> methods = util.getMethodNode(nameFilter, descFilter);

  // visitor current class
  if (methods.size() == 0) {
   System.out.println("ERROR: No method is chosen out by the filter.");
  } else {
   ClassWriter cw = new ClassWriter(0);
   BytecodeClassMethodAdder adder = new BytecodeClassMethodAdder(cw, methods);
   FileInputStream fis = new FileInputStream(des);
   ClassReader cr = new ClassReader(fis);
   cr.accept(adder, ClassReader.EXPAND_FRAMES); // need to expand frames for current end user
   if (fis != null) {
    fis.close();
   }

   // convert the specified method into current class
   byte[] bytearray = cw.toByteArray();
   FileOutputStream fos = new FileOutputStream(combine);
   fos.write(bytearray);
   fos.flush();
   fos.close();
  }
}