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用 BCEL 設計字節碼（二）直接在原方法上加指令

前一個是直接生成了一個一個方法對原方法進行調用，現在直接在原方法上進行修改
即將

public class StringBuilder

{

private String buildString(int length) {

String result = "";

for (int i = 0; i < length; i++) {

result += (char)(i%26 + 'a');

}

System.out.println(result);

return result;

}

public static void main(String[] argv) {

StringBuilder inst = new StringBuilder();

for (int i = 0; i < argv.length; i++) {

String result = inst.buildString(Integer.parseInt(argv[i]));

System.out.println("Constructed string of length " +

result.length());

}

改成：

public class StringBuilder

{

private String buildString(int length) {

System.out.println("start start start");
long starttime = System.currentTimeMillis();

String result = "";

for (int i = 0; i < length; i++) {

result += (char)(i%26 + 'a');

}

System.out.println(result);

        System.out.println("Call to buildString$impl took " +
                (System.currentTimeMillis()-starttime) + " ms.");
        System.out.println("end end end end");

return result;

}

public static void main(String[] argv) {

StringBuilder inst = new StringBuilder();

for (int i = 0; i < argv.length; i++) {

String result = inst.buildString(Integer.parseInt(argv[i]));

System.out.println("Constructed string of length " +

result.length());

}

修改代碼如下：

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);

//除掉這個原來的方法

cgen.removeMethod(method);

System.out.println("打印出這個方法看看---------------------------------start");

System.out.println(wrapgen.toString());

System.out.println("打印出這個方法看看---------------------------------end");

InstructionList ilist = wrapgen.getInstructionList();

System.out.println("看看這個方法的InstructionList-----------------------------start");

System.out.println(ilist.toString());

System.out.println("看看這個方法的InstructionList-----------------------------start");

System.out.println("看看這個方法InstructionList的各個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("看看這個方法InstructionList的各個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;//非靜態方法slot 0處應該存儲的是this

//// 這種方式與Java如何處理方法調用有關。對于非靜態的方法，每次調用的第一個（隱藏的）參數是目標對象的this引用（就是位置0儲存的內容）。

for(int i = 0;i<types.length;i++){

slot += types[i].getSize();//long,double的size為2

}

* 判斷原來的方法用到了哪些局部變量,獲得局部變量中已經用到的最大索引

* 將新產生的局部變量加到最大索引后,本來準備自己寫的

* BCEL中已經這樣的方法了

LocalVariableGen lvg = wrapgen.addLocalVariable("starttime", Type.LONG, null, null);

//先插入一條打印語句不使用局部變量

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);

//這個會不會將局部變量為2的地方的局部變量給覆蓋,然后此局部變量也沒有定義名字??slot這個index怎么來確定

//slot現在應該為2,之前代碼塊放的是result信息是aload,

//寫到新產生的局部變量的索引處

printlnList.append(InstructionFactory.createStore(Type.LONG, lvg.getIndex()));

//加入到之前的inlist中

ilist.insert(printlnList);

//在語句最后在打印結束語句,不能簡單插入在最后面,加入方法有返回值,則要插入在return 之前

//在return的時候，還要先將return的引用加入到操作數棧,怎么獲取result在局部變量中index

InstructionHandle insertposition =null;

if(returnType.getType()!=Type.VOID.getType()){

insertposition = ilist.getEnd().getPrev()；

}else{

//返回值為Type.void的話,由于沒有返回值，因此只需要在return指令前加就夠了,往前取一個即可

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);

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));

//獲取之前的的starttime局部變量

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(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");

}

posted on 2009-08-13 22:53 Frank_Fang 閱讀(1983) 評論(2) 編輯收藏所屬分類: bcel javassist

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