JWebAssembly/src/de/inetsoftware/jwebassembly/module/ClassFileLoader.java

/*
   Copyright 2020 - 2022 Volker Berlin (i-net software)

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

*/
package de.inetsoftware.jwebassembly.module;

import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;

import de.inetsoftware.classparser.ClassFile;

/**
 * Cache and manager for the loaded ClassFiles
 * 
 * @author Volker Berlin
 */
public class ClassFileLoader {

    private final HashMap<String, ClassFile>        replace   = new HashMap<>();

    //A weak cache has produce problems if there are different versions of the same class in the build path and/or library path. Then the prescan can add the second version of the class. 
    private final HashMap<String, ClassFile>        cache = new HashMap<>();

    private final ClassLoader                       loader;

    private final ClassLoader                       bootLoader;

    /**
     * Create a new instance
     * 
     * @param loader
     *            the classloader to find the *.class files
     */
    public ClassFileLoader( ClassLoader loader ) {
        this.loader = loader;
        ClassLoader cl = ClassLoader.getSystemClassLoader();
        do {
            ClassLoader parent = cl.getParent();
            if( parent == null ) {
                bootLoader = cl;
                break;
            }
            cl = parent;
        } while( true );
    }

    /**
     * Get the ClassFile from cache or load it.
     * 
     * @param className
     *            the class name like "java/lang/Object"
     * @return the ClassFile or null
     * @throws IOException
     *             If any I/O error occur
     */
    @Nullable
    public ClassFile get( String className ) throws IOException {
        ClassFile classFile = replace.get( className );
        if( classFile != null ) {
            return classFile;
        }
        classFile = cache.get( className );
        if( classFile != null ) {
            return classFile;
        }
        InputStream stream = loader.getResourceAsStream( className + ".class" );
        if( stream != null ) {
            classFile = new ClassFile( stream );
            cache.put( className, classFile );
        }
        return classFile;
    }

    /**
     * Add a class file to the weak cache.
     * 
     * @param classFile
     *            the class file
     */
    public void cache( @Nonnull ClassFile classFile ) {
        String name = classFile.getThisClass().getName();
        if( bootLoader.getResource( name + ".class" ) != null ) {
            // if the same resource is exist in the JVM self then we need to hold the reference permanently
            if( replace.get( name ) == null ) {
                // does not add a second version of the same file
                replace.put( name, classFile );
            }
        } else {
            if( cache.get( name ) == null ) {
                // does not add a second version of the same file
                cache.put( name, classFile );
            }
        }
    }

    /**
     * Replace the class in the cache with the given instance to the loader cache.
     * 
     * @param className
     *            the name of the class to replace
     * @param classFile
     *            the replacing ClassFile
     */
    void replace( String className, ClassFile classFile ) {
        if( replace.get( className ) == null ) {
            classFile = new ClassFile( className, classFile );
            replace.put( className, classFile );
        }
    }

    /**
     * Add a partial class with the given instance to the loader cache.
     * 
     * @param className
     *            the name of the class to replace like "java/lang/String"
     * @param partialClassFile
     *            the partial ClassFile
     * @throws IOException
     *             If any I/O error occur
     */
    void partial( String className, ClassFile partialClassFile ) throws IOException {
        ClassFile classFile = get( className );
        replace.put( className, classFile );
        classFile.partial( partialClassFile );
    }
}