servlet解析演进（6）-类加载器（2）
web类加载器WebappClassLoader、WebappLoader。他们俩WebappLoader是领导。webClassLoader只负责加载类这份工作，而webappLoader除了有webClassLoader实例之外还拥有容器等信息，能做些"外交"工作。
WebappLoader类的start方法被调用的时候，将会完成下面几项重要任务
（1）创建一个类加载器
（2） 设置库
（3） 设置类路径
（4） 设置访问权限
（5） 开启一个新线程用来进行自动重载
public void start() throws LifecycleException {
// Validate and update our current component state
//webapploader是否已经启动了，启动再起会跑错
if (started)
throw new LifecycleException
(sm.getString("webappLoader.alreadyStarted"));
//debug模式打印信息
if (debug >= 1)
log(sm.getString("webappLoader.starting"));
//监听器触发START_EVENT事件
lifecycle.fireLifecycleEvent(START_EVENT, null);
started = true;
//空容器，不启动类加载器
if (container.getResources() == null)
return;
// 为JNDI协议注册一个流处理工厂
URLStreamHandlerFactory streamHandlerFactory =
new DirContextURLStreamHandlerFactory();
try {
URL.setURLStreamHandlerFactory(streamHandlerFactory);
} catch (Throwable t) {
// Ignore the error here.
}
// 创建一个类加载器
try {
classLoader = createClassLoader();
classLoader.setResources(container.getResources());
classLoader.setDebug(this.debug);
classLoader.setDelegate(this.delegate);
for (int i = 0; i < repositories.length; i++) {
classLoader.addRepository(repositories[i]);
}
//设置库
setRepositories();
//设置类路径
setClassPath();
// 设置访问权限
setPermissions();
if (classLoader instanceof Lifecycle)
((Lifecycle) classLoader).start();
// 为目录上线文绑定webapp类的类加载器
DirContextURLStreamHandler.bind
((ClassLoader) classLoader, this.container.getResources());
} catch (Throwable t) {
throw new LifecycleException("start: ", t);
}
// 包访问是否合法化判断
validatePackages();
//开启一个新线程用来进行自动重载
if (reloadable) {
log(sm.getString("webappLoader.reloading"));
try {
threadStart();
} catch (IllegalStateException e) {
throw new LifecycleException(e);
}
}
}
（1）创建一个类加载器
private WebappClassLoader createClassLoader()
throws Exception {
//加载类WebappClassLoader
Class clazz = Class.forName(loaderClass);
WebappClassLoader classLoader = null;
//没有父类加载器就生成实例
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 {
//有父加载器则使用构造函数构造类实例
Class[] argTypes = { ClassLoader.class };
Object[] args = { parentClassLoader };
Constructor constr = clazz.getConstructor(argTypes);
classLoader = (WebappClassLoader) constr.newInstance(args);
}
return classLoader;
}
（2） 为加载器WebappClassLoader实例设置库
if (copyJars) {
if (!copy(jarResource.streamContent(),
new FileOutputStream(destFile)))
continue;
}
//获取jar包，并将其放置到
JarFile jarFile = new JarFile(destFile);
//为加载进来的包做处理，便于查找类是否被修改
classLoader.addJar(filename, jarFile, destFile);
}
} catch (NamingException e) {
// Silent catch: it's valid that no /WEB-INF/lib directory
// exists
} catch (IOException e) {
e.printStackTrace();
}
}
}
（3） 设置类路径
//jsp的解析器Jasper依赖classpath。将上下文属性正确设置到类路径上
private void setClassPath() {
// Validate our current state information
if (!(container instanceof Context))
return;
ServletContext servletContext =
((Context) container).getServletContext();
if (servletContext == null)
return;
StringBuffer classpath = new StringBuffer();
// Assemble the class path information from our class loader chain
ClassLoader loader = getClassLoader();
int layers = 0;
int n = 0;
while ((layers < 3) && (loader != null)) {
if (!(loader instanceof URLClassLoader))
break;
URL repositories[] =
((URLClassLoader) loader).getURLs();
for (int i = 0; i < repositories.length; i++) {
String repository = repositories[i].toString();
if (repository.startsWith("file://"))
repository = repository.substring(7);
else if (repository.startsWith("file:"))
repository = repository.substring(5);
else if (repository.startsWith("jndi:"))
repository =
servletContext.getRealPath(repository.substring(5));
else
continue;
if (repository == null)
continue;
if (n > 0)
classpath.append(File.pathSeparator);
classpath.append(repository);
n++;
}
loader = loader.getParent();
layers++;
}
//存储类路径到servlet上下文属性中
servletContext.setAttribute(Globals.CLASS_PATH_ATTR,
classpath.toString());
}
（4） 设置访问权限
private void setPermissions() {
//如果没有配置security则返回
if (System.getSecurityManager() == null)
return;
//如果上下文不是容器子类则返回
if (!(container instanceof Context))
return;
//获取servlet上下文
ServletContext servletContext =
((Context) container).getServletContext();
//找到工作控件的路径
File workDir =
(File) servletContext.getAttribute(Globals.WORK_DIR_ATTR);
if (workDir != null) {
try {
String workDirPath = workDir.getCanonicalPath();
//为类加载器添加工作空间路径为读、写可访问权限
classLoader.addPermission
(new FilePermission(workDirPath, "read,write"));
//为类加载器添加工作空间中文件有读写删除的访问权限
classLoader.addPermission
(new FilePermission(workDirPath + File.separator + "-",
"read,write,delete"));
} catch (IOException e) {
// Ignore
}
}
try {
//项目根路径
URL rootURL = servletContext.getResource("/");
classLoader.addPermission(rootURL);
//项目的绝对路径
String contextRoot = servletContext.getRealPath("/");
if (contextRoot != null) {
try {
contextRoot =
(new File(contextRoot)).getCanonicalPath()
+ File.separator;
//访问权限
classLoader.addPermission(contextRoot);
} catch (IOException e) {
// Ignore
}
}
///WEB-INF/classes/ 路径访问权限添加
URL classesURL =
servletContext.getResource("/WEB-INF/classes/");
if (classesURL != null)
classLoader.addPermission(classesURL);
///WEB-INF/lib/ 路径访问权限添加
URL libURL = servletContext.getResource("/WEB-INF/lib/");
if (libURL != null) {
classLoader.addPermission(libURL);
}
if (contextRoot != null) {
if (libURL != null) {
File rootDir = new File(contextRoot);
//项目的WEB-INF/lib/路径的权限
File libDir = new File(rootDir, "WEB-INF/lib/");
String path = null;
try {
path = libDir.getCanonicalPath() + File.separator;
} catch (IOException e) {
}
if (path != null)
classLoader.addPermission(path);
}
} else {
if (workDir != null) {
if (libURL != null) {
//项目的WEB-INF/lib/路径的权限
File libDir = new File(workDir, "WEB-INF/lib/");
String path = null;
try {
path = libDir.getCanonicalPath() + File.separator;
} catch (IOException e) {
}
classLoader.addPermission(path);
}
if (classesURL != null) {
// 项目空间的WEB-INF/lib/路径的权限
File classesDir =
new File(workDir, "WEB-INF/classes/");
String path = null;
try {
path = classesDir.getCanonicalPath()
+ File.separator;
} catch (IOException e) {
}
classLoader.addPermission(path);
}
}
}
} catch (MalformedURLException e) {
}
}
（5） 开启一个新线程用来进行自动重载
private void threadStart() {
// Has the background thread already been started?
if (thread != null)
return;
// Validate our current state
if (!reloadable)
throw new IllegalStateException
(sm.getString("webappLoader.notReloadable"));
if (!(container instanceof Context))
throw new IllegalStateException
(sm.getString("webappLoader.notContext"));
// Start the background thread
if (debug >= 1)
log(" Starting background thread");
threadDone = false;
threadName = "WebappLoader[" + container.getName() + "]";
thread = new Thread(this, threadName);
//启动WebappLoader类，将其设置为后台线程。
thread.setDaemon(true);
thread.start();
}
public void run() {
if (debug >= 1)
log("BACKGROUND THREAD Starting");
// Loop until the termination semaphore is set
while (!threadDone) {
// Wait for our check interval
threadSleep();
if (!started)
break;
try {
// 没有属性修改则继续，
if (!classLoader.modified())
continue;
} catch (Exception e) {
log(sm.getString("webappLoader.failModifiedCheck"), e);
continue;
}
// Handle a need for reloading
notifyContext();
break;
}
private void notifyContext() {
WebappContextNotifier notifier = new WebappContextNotifier();
(new Thread(notifier)).start();
}
protected class WebappContextNotifier implements Runnable {
/**
* Perform the requested notification.
*/
public void run() {
//调用容器reload方法重启服务器环境
((Context) container).reload();
}
}
参考文献：
http://blog.csdn.net/gjanyanlig/article/details/6818655
http://www.cnblogs.com/xing901022/p/4574961.html
http://blog.csdn.net/dc_726/article/details/11873343
http://lovnet.iteye.com/blog/1825322
http://www.cnblogs.com/ITtangtang/p/3978102.html
http://blog.sina.com.cn/s/blog_4fe01e630100gu3x.html
http://www.ibm.com/developerworks/cn/java/j-dclp1/
http://www.tuicool.com/articles/NrI7NrN