How Tomcat Works 读书笔记 八 载入器

Java的类载入器

详细资料见

http://blog.csdn.net/dlf123321/article/details/39957175

Loader接口

package org.apache.catalina;

import java.beans.PropertyChangeListener;

public interface Loader {
    public ClassLoader getClassLoader();
    public Container getContainer();              //载入器通常与一个context级别的容器相联
    public void setContainer(Container container);
    public DefaultContext getDefaultContext();
    public void setDefaultContext(DefaultContext defaultContext);
    public boolean getDelegate();                 //Delegate 代表 委托
    public void setDelegate(boolean delegate);    //就是类加载器是否会把加载的任务委托给其父类加载器
    public String getInfo();
    public boolean getReloadable();               //表明是否支持载入器的自动重载
    public void setReloadable(boolean reloadable);
    public void addPropertyChangeListener(PropertyChangeListener listener);
    public void addRepository(String repository);
    public String[] findRepositories();
    public boolean modified();                     //如果容器中的一个或多个类被修改了 modified就会返回true
    public void removePropertyChangeListener(PropertyChangeListenerlistener);
}

WebAppLoader类

创建类载入器

 private WebappClassLoader createClassLoader()
        throws Exception {

    //loadClass为字符串
    //默认为    private String loaderClass ="org.apache.catalina.loader.WebappClassLoader";
    //可通过setLoadClass方法更改
        Class<?> clazz = Class.forName(loaderClass);
        WebappClassLoader classLoader = null;

    //在构造WebAppLoader时 又构造函数的参数指定
        if (parentClassLoader == null) {
            // Will cause a ClassCast is the class does not extend WCL, but
            // this is on purpose (the exception will be caught and rethrown)
            classLoader = (WebappClassLoader) clazz.newInstance();
        } else {
            Class<?>[] argTypes = { ClassLoader.class };
            Object[] args = { parentClassLoader };
            Constructor<?> constr = clazz.getConstructor(argTypes);
            classLoader = (WebappClassLoader) constr.newInstance(args);
        }
        return classLoader;
    }

设置仓库

设置类路径

设置访问权限

开启新线程执行类的重新载入

 public void run() {

        if (debug >= 1)
            log("BACKGROUND THREAD Starting");

        // Loop until the termination semaphore is set
    //整段代码包含在while循环中
    //在前面threadDone已经被设置为false
    //直到程序关闭时,threadDone才会变为true
        while (!threadDone) {
            // Wait for our check interval
            threadSleep();

            if (!started)
                break;

            try {
                // Perform our modification check
                if (!classLoader.modified())
                    continue;
            } catch (Exception e) {
                log(sm.getString("webappLoader.failModifiedCheck"), e);
                continue;
            }

            // Handle a need for reloading
            notifyContext();
            break;

        }

        if (debug >= 1)
            log("BACKGROUND THREAD Stopping");

    }

    private void threadSleep() {          //让程序休眠一段时间 时间由checkInterval指定
        try {
            Thread.sleep(checkInterval * 1000L);
        } catch (InterruptedException e) {
            ;
        }
    }

 private void notifyContext() {
        WebappContextNotifier notifier = new WebappContextNotifier();
        (new Thread(notifier)).start();
    }
protected class WebappContextNotifier implements Runnable {

        /**
         * Perform the requested notification.
         */
        public void run() {
            ((Context) container).reload();
        }
    }

WebappClassLoader类

private static final String[] packageTriggers = {
    "javax", // Java extensions
    "org.xml.sax", // SAX 1 & 2
    "org.w3c.dom", // DOM 1 & 2
    "org.apache.xerces", // Xerces 1 & 2
    "org.apache.xalan" // Xalan
};

类缓存

为了达到更好的性能,会缓存已经载入的类,这样一来下次在使用这个类的时候,就不用再起加载了。

package org.apache.catalina.loader;
import java.net.URL;
import java.security.cert.Certificate;
import java.util.jar.Manifest;
public class ResourceEntry {
    public long lastModifled = -1;
    // Binary content of the resource.public byte[] binaryContent = null;
    public Class loadedClass = null;
    // URL source from where the object was loaded.
    public URL source = null;
    // URL of the codebase from where the object was loaded.
    public URL CodeBase = null;
    public Manifest manifest = null;
    public Certificate[] certificates = null;
}

参考资料

How Tomcat Works 读书笔记 八 载入器

原文：http://blog.csdn.net/dlf123321/article/details/40584923