问题
I have a class like below with a method that just returns a String, but I want to modify what it returns from another class, without hardcoding it myself.
public class Name {
public static String getName() {
return "MyName";
}
}
Is there any way to do this? I tried BCEL but that didn't seem to change the return value.
Edit: This is for a mod. I'm trying to make it completely independant from the existing code, by not modifying it.
Thanks.
回答1:
Are you sure you've tried BCEL? I created a fully-working example here.
JavaClass target;
try {
target = Repository.lookupClass("Target");
} catch (final ClassNotFoundException ex) {
throw new RuntimeException("unable to resolve Target", ex);
}
final ClassGen targetGen = new ClassGen(target);
final ConstantPoolGen pool = targetGen.getConstantPool();
final ConstantMethodref ref = (ConstantMethodref) pool.getConstant(
pool.lookupMethodref("Name", "getName", "()Ljava/lang/String;"));
ref.setClassIndex(pool.lookupClass("Target"));
ref.setNameAndTypeIndex(pool.addNameAndType("$Name$getName", "()Ljava/lang/String;"));
final InstructionList code = new InstructionList();
final InstructionFactory factory = new InstructionFactory(targetGen, pool);
code.append(factory.createConstant("overriden-name"));
code.append(factory.createReturn(Type.STRING));
code.setPositions();
final MethodGen methodGen = new MethodGen(
Constants.ACC_PRIVATE | Constants.ACC_SYNTHETIC | Constants.ACC_STATIC,
Type.STRING, new Type[0], new String[0], "$Name$getName", "Target",
code, pool);
methodGen.setMaxLocals(0);
methodGen.setMaxStack(1);
targetGen.addMethod(methodGen.getMethod());
try {
targetGen.getJavaClass().dump("Target.class");
} catch (final IOException ex) {
throw new RuntimeException("unable to save Target", ex);
}
C:\dev\scrap>javac Target.java C:\dev\scrap>java Target original-name C:\dev\scrap>javac -cp .;bcel-6.0.jar Instrumenter.java C:\dev\scrap>java -cp .;bcel-6.0.jar Instrumenter C:\dev\scrap>java Target overriden-name
回答2:
You can pass parameter into method
public class Main {
getName("newName")
}
public class Name {
public static String getName(String name) {
return name;
}
}
回答3:
You can try to add a -javaagent
agent which will use something like asm or bcel to modify the bytecode of Name
class such that the static method will return another string. Many mock testing frameworks - for e.g. powermock or jmockit - can do this.
EDIT: Here is some sample code to get you started. This is a javaagent which can modify a given public static method which returns a String
to return another constant String
. For e.g:
public class TestMain
{
public static void main(String[] args)
{
System.out.println(Name.getName());
}
}
class Name
{
public static String getName()
{
return "ORIGINAL";
}
}
$ java -cp build/libs/bciex.jar mycompany.myapp.TestMain
ORIGINAL
$ java -cp build/libs/bciex.jar -javaagent:build/libs/bciex.jar="mycompany.myapp.TestMain|getName|SOME_STRING" mycompany.myapp.TestMain
Agent loaded; will modify [getName] method of classes in [mycompany.myapp.TestMain] to return [SOME_STRING]
SOME_STRING
$
来源:https://stackoverflow.com/questions/12119720/replacing-statically-referenced-method-in-java