Find out which classes of a given API are used

In a Java Project of mine, I would like to find out programmatically which classes from a given API are used. Is there a good way to do that? Through source code parsing or bytecode parsing maybe? Beca开发者_Python百科use Reflection won't be of any use, I'm afraid.

To make things simpler: there are no wildcard imports (import com.mycompany.api.*;) anywhere in my project, no fully qualified field or variable definitions (private com.mycompany.api.MyThingy thingy;) nor any Class.forName(...) constructs. Given these limitations, it boils down to parsing import statements, I guess. Is there a preferred approach to do this?

You can discover the classes using ASM's Remapper class (believe it or not). This class is actually meant to replace all occurrences of a class name within bytecode. For your purposes, however, it doesn't need to replace anything.

This probably doesn't make a whole lot of sense, so here is an example...

First, you create a subclass of Remapper whose only purpose in life is to intercept all calls to the mapType(String) method, recording its argument for later use.

public class ClassNameRecordingRemapper extends Remapper {

    private final Set<? super String> classNames;

    public ClassNameRecordingRemapper(Set<? super String> classNames) {
        this.classNames = classNames;
    }

    @Override
    public String mapType(String type) {
        classNames.add(type);
        return type;
    }

}

Now you can write a method like this:

public Set<String> findClassNames(byte[] bytecode) {
    Set<String> classNames = new HashSet<String>();

    ClassReader classReader = new ClassReader(bytecode);
    ClassWriter classWriter = new ClassWriter(classReader, 0);

    ClassNameRecordingRemapper remapper = new ClassNameRecordingRemapper(classNames);
    classReader.accept(remapper, 0);

    return classNames;
}

It's your responsibility to actually obtain all classes' bytecode.

EDIT by seanizer (OP)

I am accepting this answer, but as the above code is not quite correct, I will insert the way I used this:

public static class Collector extends Remapper{

    private final Set<Class<?>> classNames;
    private final String prefix;

    public Collector(final Set<Class<?>> classNames, final String prefix){
        this.classNames = classNames;
        this.prefix = prefix;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String mapDesc(final String desc){
        if(desc.startsWith("L")){
            this.addType(desc.substring(1, desc.length() - 1));
        }
        return super.mapDesc(desc);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String[] mapTypes(final String[] types){
        for(final String type : types){
            this.addType(type);
        }
        return super.mapTypes(types);
    }

    private void addType(final String type){
        final String className = type.replace('/', '.');
        if(className.startsWith(this.prefix)){
            try{
                this.classNames.add(Class.forName(className));
            } catch(final ClassNotFoundException e){
                throw new IllegalStateException(e);
            }
        }
    }

    @Override
    public String mapType(final String type){
        this.addType(type);
        return type;
    }

}

public static Set<Class<?>> getClassesUsedBy(
    final String name,   // class name
    final String prefix  // common prefix for all classes
                         // that will be retrieved
    ) throws IOException{
    final ClassReader reader = new ClassReader(name);
    final Set<Class<?>> classes =
        new TreeSet<Class<?>>(new Comparator<Class<?>>(){

            @Override
            public int compare(final Class<?> o1, final Class<?> o2){
                return o1.getName().compareTo(o2.getName());
            }
        });
    final Remapper remapper = new Collector(classes, prefix);
    final ClassVisitor inner = new EmptyVisitor();
    final RemappingClassAdapter visitor =
        new RemappingClassAdapter(inner, remapper);
    reader.accept(visitor, 0);
    return classes;
}

Here's a main class to test it using:

public static void main(final String[] args) throws Exception{
    final Collection<Class<?>> classes =
        getClassesUsedBy(Collections.class.getName(), "java.util");
    System.out.println("Used classes:");
    for(final Class<?> cls : classes){
        System.out.println(" - " + cls.getName());
    }

}

And here's the Output:

Used classes:
 - java.util.ArrayList
 - java.util.Arrays
 - java.util.Collection
 - java.util.Collections
 - java.util.Collections$1
 - java.util.Collections$AsLIFOQueue
 - java.util.Collections$CheckedCollection
 - java.util.Collections$CheckedList
 - java.util.Collections$CheckedMap
 - java.util.Collections$CheckedRandomAccessList
 - java.util.Collections$CheckedSet
 - java.util.Collections$CheckedSortedMap
 - java.util.Collections$CheckedSortedSet
 - java.util.Collections$CopiesList
 - java.util.Collections$EmptyList
 - java.util.Collections$EmptyMap
 - java.util.Collections$EmptySet
 - java.util.Collections$ReverseComparator
 - java.util.Collections$ReverseComparator2
 - java.util.Collections$SelfComparable
 - java.util.Collections$SetFromMap
 - java.util.Collections$SingletonList
 - java.util.Collections$SingletonMap
 - java.util.Collections$SingletonSet
 - java.util.Collections$SynchronizedCollection
 - java.util.Collections$SynchronizedList
 - java.util.Collections$SynchronizedMap
 - java.util.Collections$SynchronizedRandomAccessList
 - java.util.Collections$SynchronizedSet
 - java.util.Collections$SynchronizedSortedMap
 - java.util.Collections$SynchronizedSortedSet
 - java.util.Collections$UnmodifiableCollection
 - java.util.Collections$UnmodifiableList
 - java.util.Collections$UnmodifiableMap
 - java.util.Collections$UnmodifiableRandomAccessList
 - java.util.Collections$UnmodifiableSet
 - java.util.Collections$UnmodifiableSortedMap
 - java.util.Collections$UnmodifiableSortedSet
 - java.util.Comparator
 - java.util.Deque
 - java.util.Enumeration
 - java.util.Iterator
 - java.util.List
 - java.util.ListIterator
 - java.util.Map
 - java.util.Queue
 - java.util.Random
 - java.util.RandomAccess
 - java.util.Set
 - java.util.SortedMap
 - java.util.SortedSet

I think the following might help you out:

1. Class Dependency Analyzer
2. Dependency Finder

1. Compiler Tree API
2. byte code analysis - the fully qualified names should be in the constant pool

Something like this perhaps:

import java.io.*;
import java.util.Scanner;
import java.util.regex.Pattern;

public class FileTraverser {

    public static void main(String[] args) {
        visitAllDirsAndFiles(new File("source_directory"));
    }

    public static void visitAllDirsAndFiles(File root) {
        if (root.isDirectory())
            for (String child : root.list())
                visitAllDirsAndFiles(new File(root, child));
        process(root);
    }

    private static void process(File f) {

        Pattern p = Pattern.compile("(?=\\p{javaWhitespace}*)import (.*);");
        if (f.isFile() && f.getName().endsWith(".java")) {
            try {
                Scanner s = new Scanner(f);
                String cls = "";
                while (null != (cls = s.findWithinHorizon(p, 0)))
                    System.out.println(cls);
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
        }
    }
}

You may want to take comments into account, but it shouldn't be too hard. You could also make sure you only look for imports before the class declaration.

I use DependencyFinder exactly for that purpose. It can analyse bytecode and extract all dependencies, then dump a report in txt or xml format (see the DependencyExtractor tool). You should be able to programatically analyse the report from your application's code.

I have integrated this in my build process in order to check that certain APIs are NOT used by an application.

You may want to use STAN for that.

The "Couplings View" visualizes the dependencies to your API in a nice graph.

If you use Eclipse. Try using the profiling tools. It doesn't only tells which classes are being used, but tells much more about it. The results will be something like:

There is a very good quickstart at:

http://www.eclipse.org/tptp/home/documents/tutorials/profilingtool/profilingexample_32.html

Thanks Adam Paynter, It helped me. But what I was looking for is to fetch the dependent classes (recursively)- which means take a feature from a projects. So, need to get all the classes associated with a particular classes and again the used classes of those classes and so on. and also get the jars. So, I Created my own Java Dependency Resolver project Which will find the dependent Classes/jars for a particular class in a Project. I am sharing it here that may come to any use of some body.