我在一个 jar 中有一个类的方法，我想用我自己的来交换它的主体。在这种情况下，我只想让方法将“GOT IT”打印到控制台并返回 true；
我正在使用系统加载器来加载 jar 的类。我正在使用反射使系统类加载器能够通过字节码加载类。这部分似乎工作正常。
我正在关注此处的方法替换示例：asm.ow2.org/current/asm-transformations.pdf。
我的代码如下：
public class Main
{
public static void main(String[] args)
{
URL[] url = new URL[1];
try
{
url[0] = new URL("file:////C://Users//emist//workspace//tmloader//bin//runtime//tmgames.jar");
verifyValidPath(url[0]);
}
catch (Exception ex)
{
System.out.println("URL error");
}
Loader l = new Loader();
l.loadobjection(url);
}
public static void verifyValidPath(URL url) throws FileNotFoundException
{
File filePath = new File(url.getFile());
if (!filePath.exists())
{
throw new FileNotFoundException(filePath.getPath());
}
}
}
class Loader
{
private static final Class[] parameters = new Class[] {URL.class};
public static void addURL(URL u) throws IOException
{
URLClassLoader sysloader = (URLClassLoader) ClassLoader.getSystemClassLoader();
Class sysclass = URLClassLoader.class;
try
{
Method method = sysclass.getDeclaredMethod("addURL", parameters);
method.setAccessible(true);
method.invoke(sysloader, new Object[] {u});
}
catch (Throwable t)
{
t.printStackTrace();
throw new IOException("Error, could not add URL to system classloader");
}
}
private Class loadClass(byte[] b, String name)
{
//override classDefine (as it is protected) and define the class.
Class clazz = null;
try
{
ClassLoader loader = ClassLoader.getSystemClassLoader();
Class cls = Class.forName("java.lang.ClassLoader");
java.lang.reflect.Method method =
cls.getDeclaredMethod("defineClass", new Class[] { String.class, byte[].class, int.class, int.class });
// protected method invocaton
method.setAccessible(true);
try
{
Object[] args = new Object[] {name, b, new Integer(0), new Integer(b.length)};
clazz = (Class) method.invoke(loader, args);
}
finally
{
method.setAccessible(false);
}
}
catch (Exception e)
{
e.printStackTrace();
System.exit(1);
}
return clazz;
}
public void loadobjection(URL[] myJar)
{
try
{
Loader.addURL(myJar[0]);
//tmcore.game is the class that holds the main method in the jar
/*
Class<?> classToLoad = Class.forName("tmcore.game", true, this.getClass().getClassLoader());
if(classToLoad == null)
{
System.out.println("No tmcore.game");
return;
}
*/
MethodReplacer mr = null;
ClassReader cr = new ClassReader("tmcore.objwin");
ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_FRAMES);
MethodVisitor mv = null;
try
{
mr = new MethodReplacer(cw, "Test", "(Ljava/lang/String;ZLjava/lang/String;)Z");
}
catch (Exception e)
{
System.out.println("Method Replacer Exception");
}
cr.accept(mr, ClassReader.EXPAND_FRAMES);
PrintWriter pw = new PrintWriter(System.out);
loadClass(cw.toByteArray(), "tmcore.objwin");
Class<?> classToLoad = Class.forName("tmcore.game", true, this.getClass().getClassLoader());
if(classToLoad == null)
{
System.out.println("No tmcore.game");
return;
}
//game doesn't have a default constructor, so we need to get the reference to public game(String[] args)
Constructor ctor = classToLoad.getDeclaredConstructor(String[].class);
if(ctor == null)
{
System.out.println("can't find constructor");
return;
}
//Instantiate the class by calling the constructor
String[] args = {"tmgames.jar"};
Object instance = ctor.newInstance(new Object[]{args});
if(instance == null)
{
System.out.println("Can't instantiate constructor");
}
//get reference to main(String[] args)
Method method = classToLoad.getDeclaredMethod("main", String[].class);
//call the main method
method.invoke(instance);
}
catch (Exception ex)
{
System.out.println(ex.getMessage());
ex.printStackTrace();
}
}
}
public class MethodReplacer extends ClassVisitor implements Opcodes
{
private String mname;
private String mdesc;
private String cname;
public MethodReplacer(ClassVisitor cv, String mname, String mdesc)
{
super(Opcodes.ASM4, cv);
this.mname = mname;
this.mdesc = mdesc;
}
public void visit(int version, int access, String name, String signature,
String superName, String[] interfaces)
{
this.cname = name;
cv.visit(version, access, name, signature, superName, interfaces);
}
public MethodVisitor visitMethod(int access, String name, String desc, String signature,
String[] exceptions)
{
String newName = name;
if(name.equals(mname) && desc.equals(mdesc))
{
newName = "orig$" + name;
generateNewBody(access, desc, signature, exceptions, name, newName);
System.out.println("Replacing");
}
return super.visitMethod(access, newName, desc, signature, exceptions);
}
private void generateNewBody(int access, String desc, String signature, String[] exceptions,
String name, String newName)
{
MethodVisitor mv = cv.visitMethod(access, name, desc, signature, exceptions);
mv.visitCode();
mv.visitVarInsn(Opcodes.ALOAD, 0);
mv.visitMethodInsn(access, cname, newName, desc);
mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");
mv.visitLdcInsn("GOTit!");
mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V");
mv.visitInsn(ICONST_0);
mv.visitInsn(IRETURN);
mv.visitMaxs(0, 0);
mv.visitEnd();
}
}
问题似乎mv.visitMethodInsn(access, cname, newName, desc);在generateMethodBody里面MethodReplacer。
我收到“常量池中的非法类型”错误。
我不确定我错过了什么……但是在阅读和测试了大约 3 天之后，我仍然没有得到任何结果。
[编辑]
如果您想知道，tmcore这是一个律师的单人“异议”游戏。我这样做是为了好玩。该程序成功启动了游戏，一切都很好，删除修改MethodReplacer使游戏按设计运行。所以这个问题似乎与我在方法替换器中的错误字节码/修改有关。
[编辑2]
CheckClassAdapter.verify(cr, true, pw);返回函数在编辑之前应该具有的完全相同的字节码。就好像没有进行更改一样。
[编辑3]
classtoload根据评论注释掉的副本