写一个工具可以在服务端执行临时代码

字节工具类

作用转化int和字符串相互转换

package com.kailong.classloader; /** * Created by Administrator on 2017/4/4. */ public class ByteUtils { public static int bytes2Int(byte[] classByte, int start, int len) { int sum=0; int end=start+len; for(int i=start;i<end;i++){ int n=((int)classByte[i])&0xff; n<<=(--len)*8; sum=n+sum; } return sum; } public static byte[] int2Bytes(int value,int len){ byte[]b=new byte[len]; for(int i=0;i<len;i++){ b[len-i-1]=(byte)((value>>8*i)&0xff); } return b; } public static String bytes2String(byte[] str,int start,int len){ return new String(str,start,len); } public static byte[] string2Bytes(String str){ return str.getBytes(); } public static byte[] bytesReplace(byte[] originalBytes,int offset,int len,byte[] replaceBytes){ byte[] newBytes=new byte[originalBytes.length+(replaceBytes.length-len)]; System.arraycopy(originalBytes,0,newBytes,0,offset); System.arraycopy(replaceBytes,0,newBytes,offset,replaceBytes.length); System.arraycopy(originalBytes,offset+len,newBytes,offset+replaceBytes.length,originalBytes.length-offset-len); return newBytes; } } package com.kailong.classloader; import javax.print.DocFlavor; /** * Created by Administrator on 2017/4/4. * 修改class文件 修改常量池常量的功能 可以拓展 */ public class ClassModifier { private static final int CONSTANT_POOL_INDEX=8; private static final int CONSTANT_Utf8_info=1; private static final int[] CONSTANT_ITEM_LENGTH={-1,-1,-1,5,5,9,9,3,3,5,5,5,5}; private static final int u1=1; private static final int u2=2; private byte[] classByte; public ClassModifier(byte[] classByte){ this.classByte=classByte; } public byte[] modifyUTF8Constant(String oldStr,String newStr){ int cpc=getConstantPollCount(); int offset=CONSTANT_POOL_INDEX+u2; for(int i=0;i<cpc;i++){ int tag=ByteUtils.bytes2Int(classByte,offset,u1); if(tag==CONSTANT_Utf8_info){ int len= ByteUtils.bytes2Int(classByte,offset+u1,u2); offset+=(u1+u2); String str=ByteUtils.bytes2String(classByte,offset,len); if(str.equalsIgnoreCase(oldStr)){ byte[] strBytes=ByteUtils.string2Bytes(newStr); byte[] strLen=ByteUtils.int2Bytes(newStr.length(),u2); classByte=ByteUtils.bytesReplace(classByte,offset-u2,u2,strLen); classByte=ByteUtils.bytesReplace(classByte,offset,len,strBytes); return classByte; }else { offset+=len;; } }else { offset+=CONSTANT_ITEM_LENGTH[tag]; } } return classByte; } private int getConstantPollCount() { return ByteUtils.bytes2Int(classByte,CONSTANT_POOL_INDEX,u2); } } package com.kailong.classloader; import java.io.ByteArrayOutputStream; import java.io.InputStream; import java.io.PrintStream; /** * Created by Administrator on 2017/4/4. */ public class HackSystem { public final static InputStream in=System.in; private static ByteArrayOutputStream buff=new ByteArrayOutputStream(); public final static PrintStream out=new PrintStream(buff); public final static PrintStream err=out; public static String getBufferString(){ return buff.toString(); } public static void clearBuffer(){ buff.reset(); } public static void setSecurityManager(final SecurityManager s){ System.setSecurityManager(s); } public static SecurityManager getSecurityManager(){ return System.getSecurityManager(); } public static long currrentTimeMillis(){ return System.currentTimeMillis(); } public static int identitiHashcode(Object o){ return System.identityHashCode(o); } public static void arraycopy(Object src,int srcPos,Object dest,int destPos,int length){ System.arraycopy(src,srcPos,dest,destPos,length); } } package com.kailong.classloader; /** * Created by Administrator on 2017/4/4. * 为了多次执行而加入加载器 */ public class HotSwapClassLoader extends ClassLoader{ public HotSwapClassLoader(){ super(HotSwapClassLoader.class.getClassLoader()); } public Class loadByte(byte[] classByte){ return defineClass(null,classByte,0,classByte.length); } } package com.kailong.classloader; import java.lang.reflect.Method; /** * Created by Administrator on 2017/4/4. */ public class JavaClassExecuter { public static String execute(byte[] classByte){ HackSystem.clearBuffer(); ClassModifier classModifier=new ClassModifier(classByte); byte[] modiBytes= classModifier.modifyUTF8Constant("java/lang/System","com/kailong/classloader/HackSystem"); HotSwapClassLoader loader=new HotSwapClassLoader(); Class clazz = loader.loadByte(modiBytes); try{ Method method=clazz.getMethod("main",new Class[]{String[].class}); method.invoke(null,new String[]{null}); }catch (Throwable e){ e.printStackTrace(); } return HackSystem.getBufferString(); } }

效果

测试class 代码

public class Test{ public static void main(String [] args){ System.out.println("11111111111111111111111111111"); for(int i=0;i<=100;i++){ System.out.println("likailong"+i); } } } 拓展可以从文本框读取类。远程执行功能。