用 BCEL 设计字节码: 直接在原方法上加指令
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修改代码如下:
import java.io.FileOutputStream;
import java.util.Iterator;
import org.apache.bcel.Constants;
import org.apache.bcel.classfile.ClassParser;
import org.apache.bcel.classfile.JavaClass;
import org.apache.bcel.classfile.LineNumberTable;
import org.apache.bcel.classfile.LocalVariableTable;
import org.apache.bcel.classfile.Method;
import org.apache.bcel.generic.ClassGen;
import org.apache.bcel.generic.ConstantPoolGen;
import org.apache.bcel.generic.InstructionConstants;
import org.apache.bcel.generic.InstructionFactory;
import org.apache.bcel.generic.InstructionHandle;
import org.apache.bcel.generic.InstructionList;
import org.apache.bcel.generic.InvokeInstruction;
import org.apache.bcel.generic.LocalVariableGen;
import org.apache.bcel.generic.MethodGen;
import org.apache.bcel.generic.ObjectType;
import org.apache.bcel.generic.PUSH;
import org.apache.bcel.generic.Type;
public class BCELTiming2 {
private static void modifyWrapper(ClassGen cgen,Method method){
InstructionFactory ifact = new InstructionFactory(cgen);
ConstantPoolGen pgen = cgen.getConstantPool();
String cname = cgen.getClassName();
MethodGen wrapgen = new MethodGen(method,cname,pgen);
//除掉这个原来的方法
cgen.removeMethod(method);
System.out.println("打印出这个方法看看---------------------------------start");
System.out.println(wrapgen.toString());
System.out.println("打印出这个方法看看---------------------------------end");
InstructionList ilist = wrapgen.getInstructionList();
System.out.println("看看这个方法的InstructionList-----------------------------start");
System.out.println(ilist.toString());
System.out.println("看看这个方法的InstructionList-----------------------------start");
System.out.println("看看这个方法InstructionList的各个InstructionHandle的信息--------------------start");
Iterator handleIt = ilist.iterator();
while(handleIt.hasNext()){
InstructionHandle iHandle = (InstructionHandle)handleIt.next();
System.out.println(iHandle.getAttributes());
System.out.println(iHandle.toString());
}
System.out.println("看看这个方法InstructionList的各个InstructionHandle的信息--------------------end");
System.out.println("先看看此方法的LocalVariableTable的信息--------------------------------------start");
LocalVariableTable lvt = wrapgen.getLocalVariableTable(pgen);
System.out.println(lvt.toString());
System.out.println("先看看此方法的LocalVariableTable的信息--------------------------------------end");
LineNumberTable lnt = wrapgen.getLineNumberTable(pgen);
System.out.println("LineNumberTable--------------------------------------start");
System.out.println(lnt.toString());
System.out.println("LineNumberTable--------------------------------------end");
Type returnType = wrapgen.getReturnType();
Type[] types = wrapgen.getArgumentTypes();
int slot = wrapgen.isStatic()?0:1;//非静态方法slot 0处应该存储的是this
//// 这种方式与Java如何处理方法调用有关。对于非静态的方法,每次调用的第一个(隐藏的)参数是目标对象的this引用(就是位置0储存的内容)。
for(int i = 0;i<types.length;i++){
slot += types[i].getSize();//long,double的size为2
}
/**//*
* 判断原来的方法用到了哪些局部变量,获得局部变量中已经用到的最大索引
* 将新产生的局部变量加到最大索引后,本来准备自己写的
* BCEL中已经这样的方法了
*/
LocalVariableGen lvg = wrapgen.addLocalVariable("starttime", Type.LONG, null, null);
//先插入一条打印语句不使用局部变量
InstructionList printlnList = ifact.createPrintln("start test start test start test start test");
InvokeInstruction invokestatic = ifact.createInvoke("java.lang.System",
"currentTimeMillis", Type.LONG, Type.NO_ARGS, Constants.INVOKESTATIC);
InstructionHandle firstHandle = printlnList.append(invokestatic);
//这个会不会将局部变量为2的地方的局部变量给覆盖,然后此局部变量也没有定义名字??slot这个index怎么来确定
//slot现在应该为2,之前代码块放的是result信息是aload,
//写到新产生的局部变量的索引处
printlnList.append(InstructionFactory.createStore(Type.LONG, lvg.getIndex()));
//加入到之前的inlist中
ilist.insert(printlnList);
//
//在语句最后在打印结束语句,不能简单插入在最后面,加入方法有返回值,则要插入在return 之前
//在return的时候,还要先将return的引用加入到操作数栈,怎么获取result在局部变量中index
InstructionHandle insertposition =null;
if(returnType.getType()!=Type.VOID.getType()){
insertposition = ilist.getEnd().getPrev();
}else{
//返回值为Type.void的话,由于没有返回值,因此只需要在return指令前加就够了,往前取一个即可
insertposition = ilist.getEnd();
}
InstructionList tempList = new InstructionList();
tempList.append(ifact.createFieldAccess("java.lang.System"
, "out", new ObjectType("java.io.PrintStream"),
Constants.GETSTATIC));
tempList.append(InstructionFactory.DUP);
tempList.append(InstructionFactory.DUP);
String text = "Call to method "+wrapgen.getName()+" took ";
tempList.append(new PUSH(pgen,text));
tempList.append(ifact.createInvoke("java.io.PrintStream",
"print", Type.VOID, new Type[]{Type.STRING},
Constants.INVOKEVIRTUAL));
tempList.append(ifact.createInvoke("java.lang.System",
"currentTimeMillis", Type.LONG, Type.NO_ARGS,
Constants.INVOKESTATIC));
//获取之前的的starttime局部变量
tempList.append(InstructionFactory.createLoad(Type.LONG, lvg.getIndex()));
tempList.append(InstructionConstants.LSUB);
tempList.append(ifact.createInvoke("java.io.PrintStream",
"print", Type.VOID, new Type[]{Type.LONG},
Constants.INVOKEVIRTUAL));
tempList.append(new PUSH(pgen," ms."));
tempList.append(ifact.createInvoke("java.io.PrintStream",
"println", Type.VOID, new Type[]{Type.STRING},
Constants.INVOKEVIRTUAL));
//在return之前的最后一句是打印end end end.信息
tempList.append(ifact.createPrintln("end end end end end end end end end end"));
ilist.insert(insertposition,tempList);
// LocalVariableGen lvgen = new LocalVariableGen(slot,"start",Type.LONG,null,null);
//finalize the construted method
wrapgen.stripAttributes(false);
wrapgen.setMaxStack();
wrapgen.setMaxLocals();
cgen.addMethod(wrapgen.getMethod());
System.out.println();
System.out.println();
System.out.println(wrapgen.getInstructionList());
ilist.dispose();
}
public static void main(String[] args) {
args[0]="D:\\java to eclipse\\javaeclipsestudy\\workspace\\BCELTest\\bin\\StringBuilder.class";
args[1]="buildString";
String targetClassfile = "StringBuilder.class";
if(args.length==2 && args[0].endsWith(".class")){
try{
JavaClass jclas = new ClassParser(args[0]).parse();
ClassGen cgen = new ClassGen(jclas);
Method[] methods = jclas.getMethods();
int index;
for(index =0;index<methods.length;index++){
if(methods[index].getName().equals(args[1])){
break;
}
}
if(index<methods.length){
modifyWrapper(cgen,methods[index]);
FileOutputStream fos = new FileOutputStream(targetClassfile);
cgen.getJavaClass().dump(fos);
fos.close();
}else{
System.err.println("Method " + args[1]+"not found in"+ args[0]);
}
}catch(Exception e){
e.printStackTrace();
}
}else{
System.out.println("usage: class-file method-name");
}
}
}
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