Java Reflection: Find method usage in custom Abstr

问题:

I'm newbie in reflection. Is there any way to detect where is an specific method invoked? For example:

public class MyClass {

   public static void method(){ 
       //DO SOMETHING
   }

}

public class Test {

    public test(){
       MyClass.method();
    }

}

public class MyProcessor extends AbstractProcessor {

   public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {

      Method method = MyClass.class.getDeclaredMethod("method");

      Class classWhereMethodIsInvoked = obtainClassWhereMethodIsInvoked(method); 

   }

   public Class obtainClassWhereMethodIsInvoked(Method method) {
      //here I want to search one class that invoke that method, in this case Test.class
   }

}

is something like this possible or I am going crazy?

回答1:

Yes it doable if you really want it. You can use the classLoader to search through the class path and scan for the method name through all the class files. Below is a very simplistic example to show that it is doable. In the example below I find usage of the "println" method being used in this class. Essentially you can just broaden the scope from one file in my example to all the class files.

public class SearchClasses {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) throws FileNotFoundException {


//      InputStream is = SearchClasses.class.getClassLoader().getResourceAsStream("resources.SearchClasses.class");
        InputStream is = new FileInputStream(new File("build/classes/resources/SearchClasses.class"));

        boolean found = false;
        Scanner scanner = new Scanner(is);
        while (scanner.hasNext()) {
            if (scanner.nextLine().contains("println")) {
                System.out.print("println found");
                found = true;
                break;
            }
        }

        if (!found) {
                System.out.print("println NOT found");          
        }

    }

    public static void testMethod() {
        System.out.println("testing");
    }

}

In my IDE I had to use the FileInputStream to access the class file I was searching in.... but if you are searching through jar files then you can use the classLoader instead. You would need mechanism to search through all of the class path... this is not impossible but I left it our for brevity.

EDIT: Here is an attempt to get it working completely.. searches all files in class path for your method.

public class SearchClasses {

    /**
     * @param args the command line arguments
     * @throws java.io.FileNotFoundException
     */
    public static void main(String[] args) throws FileNotFoundException, IOException {

        printAllFileWithMethod("println");
    }

    public static void printAllFileWithMethod(String methodName) throws FileNotFoundException, IOException {
        Enumeration<URL> roots = SearchClasses.class.getClassLoader().getResources("");

        List<File> allClassFiles = new ArrayList<>();
        while (roots.hasMoreElements()) {
            File root = new File(roots.nextElement().getPath());
            allClassFiles.addAll(getFilesInDirectoryWithSuffix(root, "class"));
        }

        for (File classFile : allClassFiles) {
            InputStream is = new FileInputStream(classFile);

            boolean found = false;
            Scanner scanner = new Scanner(is);
            while (scanner.hasNext()) {
                if (scanner.nextLine().contains(methodName)) {
                    System.out.print(methodName + " found in " + classFile.getName() + "\n");
                    found = true;
                    break;
                }
            }

        }
    }

    public static void testMethod() {
        System.out.println("testing");
    }

    static List<File> getFilesInDirectoryWithSuffix(File dir, String suffix) {
        List<File> foundFiles = new ArrayList<>();
        if (!dir.isDirectory()) {
            return foundFiles;
        }
        for (File file : dir.listFiles()) {
            if (file.isDirectory()) {
                foundFiles.addAll(getFilesInDirectoryWithSuffix(file, suffix));
            } else {
                String name = file.getName();
                if (name.endsWith(suffix)) {
                    foundFiles.add(file);
                }
            }

        }
        return foundFiles;
    }

}

回答2:

As mentioned in the comments, Apache BCEL is suitable for your problem. Such libraries are often particularly used for determining compile-time information such as method usage and control flow analysis from the generated bytecode, and such information are difficult, if not impossible, to retrieve using reflection. If you use the BCEL solution, you probably no longer require a custom annotation processor.

But since you already seem to be using a custom annotation processor, the whole point of it is to be able to process annotations in the source files. So one way is to define a custom annotation that marks a method being called, and have the custom processor read these annotations to know which classes call which methods:

@CallerClass("MyClass.method")
public class Test {

    public test() {
       MyClass.method();
    }

} 

In the above (trivial) example, a custom CallerClass annotation marks that a class calls the method specified in the annotation's element inside parentheses. The annotation processor can read this annotation and construct the caller information.

回答3:

You could define your own mechanism. Use a Map to store the caller of each method :

public static Map<Method, List<String>> callStack = new HashMap<Method, List<String>>();

public static void registerCaller(Method m)
{
    List<String> callers = callStack.get(m);
    if (callers == null)
    {
        callers = new ArrayList<String>();
        callStack.put(m, callers);
    }

    StackTraceElement[] stackTraceElements = Thread.currentThread().getStackTrace();
    callers.add(stackTraceElements[3].getClassName());
}

The target class :

class MyClass
{   
    public static void method()
    {
        registerCaller(new Object(){}.getClass().getEnclosingMethod());
        // DO SOMETHING
    }
}

Some caller classes :

package the.package.of;

class Test
{
    public void test()
    {
       MyClass.method();
    }
}

class Foo
{
    public void bar()
    {
       MyClass.method();
    }
}

And finally, the test :

new Test().test();
new Foo().bar();

Method method = MyClass.class.getDeclaredMethod("method");
for (String clazz : callStack.get(method))
{
    System.out.println(clazz);
}

Prints :

the.package.of.Test
the.package.of.Foo

回答4:

Well, if you use Eclipse as an IDE, you can find the complete call hierarchy via "Open Call Hierarchy" function. This will find all usages of your method in any open Eclipse projects. However, if you want to find out during runtime programmatically, then you need to integrate some library, that can statically analyze the bytecode of your classpath for use of your method.

回答5:

You can obtain stack trace right inside the test method:

public class Test {

    public void test() {
        System.out.println(getCallerClass());
    }

    public static String getCallerClass()  {
        for (StackTraceElement e: Thread.currentThread().getStackTrace()) {
            if (!"java.lang.Thread".equals(e.getClassName()) && !e.getClassName().equals(Test.class.getName()))
               return e.getClassName();
        }
        return null;
    }
}