Java生成的Protobuf反射，但没有找到类

Question

I've used protobuf a lot. But today, when I tried to use reflection on a generated protobuf class, I got a class not found exception. (I know it's not a normal protobuf usecase). The class was being used in the same file by other methods, and it's compiled and ran without problems.

import com.foo.protobuf.Foo.Bar;
...
void method1() {
    Bar.Builder bld = Bar.newBuilder();
    ...
}


void method2(String clsName) {
    // clsName = "com.foo.protobuf.Foo.Bar"
    Class clsBar = Class.forName(clsName); // CNF Exception here
}

What's wrong with my code? Thanks for any input.

Answer 1

Just found out it has nothing to do with protobuf. It's about how to refer an inner class.

All generated protobuf classes are static inner classes. In order to make it work, I have to use '$' instead of '.' to denote the last part of the fully qualified classname: Class.forName("com.foo.protobuf.Foo$Bar").

Sorry for answering my own question. Hope it helps someone who is in the same situation.

Answer 2

Everything is perfect.

possibility of issue.

Your classpath is broken (which is a very common problem in the Java world).

If you know the path of the class or the jar containing the class then add it to your classpath while running it. You can use the classpath as mentioned here:

on Windows

java -classpath .;yourjar.jar YourMainClass
on UNIX/Linux

java -classpath .:yourjar.jar YourMainClass

in your case answer is

All generated protobuf classes are static inner classes. In order to make it work, I have to use '$' instead of '.' to denote the last part of the fully qualified classname: Class.forName("com.foo.protobuf.Foo$Bar").