javassist改类

package agent;

import javassist.CannotCompileException;
import javassist.ClassPool;
import javassist.CtBehavior;
import javassist.CtClass;

import java.io.*;

public class Test {
    public static void main(String []f) throws IOException, CannotCompileException {


        ClassPool classPool = new ClassPool(true);

        InputStream inputStream = Test.class.getClassLoader().getResourceAsStream("agent/Test.class");
        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();

        byte [] bytes = new byte[1000];
        int n = 0;
        while(-1 != (n=inputStream.read(bytes))) {
            byteArrayOutputStream.write(bytes, 0, n);
        }
        CtClass ctClass = classPool.makeClass(new ByteArrayInputStream(byteArrayOutputStream.toByteArray()));
        for(CtBehavior ctBehavior : ctClass.getDeclaredBehaviors()) {
            System.out.println("start handle medthod: " + ctBehavior.getLongName());
            try {
                ctBehavior.insertBefore("System.out.println(\"b\");");
                ctBehavior.insertAfter("System.out.println(\"a\");");

            } catch (Exception e) {
                e.printStackTrace();
            }

        }
        byte [] out =  ctClass.toBytecode();
        FileOutputStream fileOutputStream = new FileOutputStream("tmp.class");
        fileOutputStream.write(out);
        fileOutputStream.close();

假如：

ClassPool classPool = new ClassPool();

start handle medthod: agent.Test()
javassist.CannotCompileException: [source error] no such class: System.out
at javassist.CtBehavior.insertBefore(CtBehavior.java:774)
at javassist.CtBehavior.insertBefore(CtBehavior.java:734)
at agent.Test.main(Test.java:28)
Caused by: compile error: no such class: System.out
at javassist.compiler.MemberResolver.searchImports(MemberResolver.java:470)
at javassist.compiler.MemberResolver.lookupClass(MemberResolver.java:414)
at javassist.compiler.MemberResolver.lookupClassByJvmName(MemberResolver.java:321)
at javassist.compiler.TypeChecker.atCallExpr(TypeChecker.java:683)
at javassist.compiler.JvstTypeChecker.atCallExpr(JvstTypeChecker.java:157)
at javassist.compiler.ast.CallExpr.accept(CallExpr.java:46)
at javassist.compiler.CodeGen.doTypeCheck(CodeGen.java:242)
at javassist.compiler.CodeGen.atStmnt(CodeGen.java:330)
at javassist.compiler.ast.Stmnt.accept(Stmnt.java:50)
at javassist.compiler.Javac.compileStmnt(Javac.java:567)
at javassist.CtBehavior.insertBefore(CtBehavior.java:754)
... 2 more
start handle medthod: agent.Test.main(java.lang.String[])
javassist.CannotCompileException: cannot find java.lang.String[]
at javassist.CtBehavior.insertBefore(CtBehavior.java:771)
at javassist.CtBehavior.insertBefore(CtBehavior.java:734)
at agent.Test.main(Test.java:28)
Caused by: javassist.NotFoundException: java.lang.String[]
at javassist.ClassPool.get(ClassPool.java:445)
at javassist.bytecode.Descriptor.toCtClass(Descriptor.java:592)
at javassist.bytecode.Descriptor.getParameterTypes(Descriptor.java:439)
at javassist.CtBehavior.getParameterTypes(CtBehavior.java:298)
at javassist.CtBehavior.insertBefore(CtBehavior.java:749)
... 2 more
start handle medthod: agent.Test.print(int)
javassist.CannotCompileException: [source error] no such class: System.out
at javassist.CtBehavior.insertBefore(CtBehavior.java:774)
at javassist.CtBehavior.insertBefore(CtBehavior.java:734)
at agent.Test.main(Test.java:28)
Caused by: compile error: no such class: System.out
at javassist.compiler.MemberResolver.lookupClass(MemberResolver.java:402)
at javassist.compiler.MemberResolver.lookupClassByJvmName(MemberResolver.java:321)
at javassist.compiler.TypeChecker.atCallExpr(TypeChecker.java:683)
at javassist.compiler.JvstTypeChecker.atCallExpr(JvstTypeChecker.java:157)
at javassist.compiler.ast.CallExpr.accept(CallExpr.java:46)
at javassist.compiler.CodeGen.doTypeCheck(CodeGen.java:242)
at javassist.compiler.CodeGen.atStmnt(CodeGen.java:330)
at javassist.compiler.ast.Stmnt.accept(Stmnt.java:50)
at javassist.compiler.Javac.compileStmnt(Javac.java:567)
at javassist.CtBehavior.insertBefore(CtBehavior.java:754)
... 2 more