import com.sun.org.apache.bcel.internal.generic.ClassGen; //导入依赖的package包/类
@Test
public void test() throws Exception {
    String classfile = getClass().getResource("Bug8003147Test.class").getPath();
    JavaClass jc = new ClassParser(classfile).parse();
    // rename class
    ConstantPool cp = jc.getConstantPool();
    int cpIndex = ((ConstantClass) cp.getConstant(jc.getClassNameIndex())).getNameIndex();
    cp.setConstant(cpIndex, new ConstantUtf8("Bug8003147TestPrime"));
    ClassGen gen = new ClassGen(jc);
    Method[] methods = jc.getMethods();
    int index;
    for (index = 0; index < methods.length; index++) {
        if (methods[index].getName().equals("doSomething")) {
            break;
        }
    }
    Method m = methods[index];
    MethodGen mg = new MethodGen(m, gen.getClassName(), gen.getConstantPool());
    gen.replaceMethod(m, mg.getMethod());
    String path = classfile.replace("Bug8003147Test", "Bug8003147TestPrime");
    gen.getJavaClass().dump(new FileOutputStream(path));

    try {
        Class.forName("Bug8003147TestPrime");
    } catch (ClassFormatError cfe) {
        cfe.printStackTrace();
        Assert.fail("modified version of class does not pass verification");
    }
}
 

import com.sun.org.apache.bcel.internal.generic.ClassGen; //导入依赖的package包/类
@Test
public void test() throws Exception {
    // Note: Because BCEL library is always behind java version, to make sure
    // JavaClass can parse the class file, create a separate
    // Bug8003147TestClass.java, which only uses basic features.
    JAXPTestUtilities.tryRunWithTmpPermission(() -> {
        String classfile = getSystemProperty("test.classes") + "/parsers/Bug8003147TestClass.class";
        JavaClass jc = new ClassParser(classfile).parse();

        // rename class
        ConstantPool cp = jc.getConstantPool();
        int cpIndex = ((ConstantClass) cp.getConstant(jc.getClassNameIndex())).getNameIndex();
        cp.setConstant(cpIndex, new ConstantUtf8("parsers/Bug8003147TestClassPrime"));
        ClassGen gen = new ClassGen(jc);
        Method[] methods = jc.getMethods();
        int index;
        for (index = 0; index < methods.length; index++) {
            if (methods[index].getName().equals("doSomething")) {
                break;
            }
        }
        Method m = methods[index];
        MethodGen mg = new MethodGen(m, gen.getClassName(), gen.getConstantPool());

        // @bug 8064516, not currently used directly by JAXP, but we may need
        // to modify preexisting methods in the future.
        InstructionFactory f = new InstructionFactory(gen);
        InstructionList il = mg.getInstructionList();
        InstructionList newInst = new InstructionList();
        newInst.append(f.createPrintln("Hello Sekai!"));
        il.insert(newInst);
        mg.setMaxStack();

        gen.replaceMethod(m, mg.getMethod());
        String path = classfile.replace("Bug8003147TestClass", "Bug8003147TestClassPrime");
        gen.getJavaClass().dump(new FileOutputStream(path));

        try {
            Class.forName("parsers.Bug8003147TestClassPrime");
        } catch (ClassFormatError cfe) {
            cfe.printStackTrace();
            Assert.fail("modified version of class does not pass verification");
        }
    }, new FilePermission(getSystemProperty("test.classes") + "/-", "read,write"));
}