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The spring component framework is used to setup a plugin based, micro-kernel, standalone application (today, we will support webapp in later releases) which is based on SpringFramework. It can help you decouple your application into several components clearly with zero invasion and keep your application consistent between develop time and runtime.
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/**
 * @author XiongJie, Date: 13-9-22
 */
package net.happyonroad.component.classworld;

import net.happyonroad.component.core.Component;
import org.codehaus.plexus.classworlds.realm.ClassRealm;
import org.codehaus.plexus.classworlds.realm.DuplicateRealmException;
import org.codehaus.plexus.classworlds.strategy.Strategy;

import java.io.IOException;
import java.lang.reflect.Field;
import java.net.URL;
import java.util.*;

/**
 * 扩展 plexus 的缺省 class realm的对象
 */
public class PomClassRealm extends ClassRealm implements Comparable{
    private PomClassWorld         pomWorld;
    private Component             component;
    private SortedSet dependedRealms;
    /*暂时不支持 depends parent == depends parent's all modules*/
    /*如果需要这个特性，那么也应该在组件之间建立depends关系的时候直接翻译为对parent的modules的依赖*/
    //private SortedSet moduleRealms;

    public PomClassRealm(PomClassWorld world, Component component) {
        super(world, component.getId(), getParentClassLoader(world, component));
        this.pomWorld = world;
        this.component = component;
        URL url = this.component.getJarFileURL();
        if (url != null) addURL(url);
        //将所有的第三方包的类由一个统一的class loader加载，管理
        //而后这个class loader面向不同的组件，有许多 representation
        //跨过各种依赖关系，直接将第三方包依赖加到本身上，加速系统启动过程中的Class Load过程
        Set libUrls = this.component.getDependedPlainURLs();
        if(libUrls != null){
            ClassLoaderRepresentation representation = new ClassLoaderRepresentation(libUrls);
            setParentClassLoader(representation);
        }
    }

    // ------------------------------------------------------------
    //     扩展功能，从dependencies里面加载类，资源
    // ------------------------------------------------------------

    public Class loadClassFromDepends(String name) {
        for (ClassRealm dependedRealm : dependedRealms) {
            try {
                return dependedRealm.loadClass(name);
            } catch (ClassNotFoundException e) {
                /*continue; to try next realm*/
            }
        }
        return null;
    }

    public URL loadResourceFromDepends(String name) {
        for (ClassRealm dependedRealm : dependedRealms) {
            URL resource = dependedRealm.getResource(name);
            if( resource != null)
                return resource;
        }
        return null;
    }

    public Enumeration loadResourcesFromDepends(String name) {
        ArrayList founds = new ArrayList();
        for (ClassRealm dependedRealm : dependedRealms) {
            Enumeration resources = null;
            try {
                resources = dependedRealm.getResources(name);
            } catch (IOException e) {
                /*continue;*/
            }
            if(resources != null ){
                while (resources.hasMoreElements()) {
                    URL url = resources.nextElement();
                    founds.add(url);
                }
            }
        }
        return Collections.enumeration(founds);
    }

    // ------------------------------------------------------------
    //     对 PomClassRealm的扩展
    // ------------------------------------------------------------

    void afterConstruction(){
        customizeStrategy();
        dependRealms();
        //createModuleRealms();
    }

    protected void customizeStrategy() {
        try{
            Field strategyField = getClass().getSuperclass().getDeclaredField("strategy");
            strategyField.setAccessible(true);
            Strategy strategy = new PomStrategy(this);
            strategyField.set(this, strategy);
        }catch (Exception ex){
            throw new UnsupportedOperationException("The parent ClassRealm don't support PomClassRealm hacking by refection", ex);
        }
    }

    protected void dependRealms() {
        dependedRealms = new TreeSet();
            for(Component depended : component.getAllDependedComponents()){
                if(depended.isPlain())continue;//所有的第三方包不再提供class realm
                PomClassRealm dependedRealm = findOrCreateRealm(pomWorld, depended);
                dependedRealms.add(dependedRealm);
            }
    }

    @Override
    public int compareTo(PomClassRealm another) {
        return this.component.compareTo(another.component);
    }

    //    protected void createModuleRealms() {
//        moduleRealms = new TreeSet();
//        if(component.getModules() != null && component.getModules().isEmpty()){
//            for(Component module : component.getModules()){
//                PomClassRealm moduleRealm = findOrCreateRealm(pomWorld, module);
//                moduleRealms.add(moduleRealm);
//            }
//        }
//    }

    static ClassLoader getParentClassLoader(PomClassWorld world, Component component) {
        Component parent = component.getParent();
        if (parent == null || parent.isPlain()) {
            //采用一个隔离的Class Loader的根，而不是当前运行环境的根
            return ClassLoader.getSystemClassLoader();
        } else {
            return findOrCreateRealm(world, parent);
        }
    }

    static PomClassRealm findOrCreateRealm(PomClassWorld world, Component component){
        PomClassRealm existRealm = world.getClassRealm(component);
        if(existRealm != null )
            return existRealm;
        try {
            return world.newRealm(component);
        } catch (DuplicateRealmException e) {
            throw new IllegalStateException("I'v checked the realm/component duplication, but it occurs." +
                                                    " this error occurred by concurrent issue!");
        }
    }
}