标签：tomcat 源码 缓存 delegate security
public Servlet loadServlet() throws ServletException {
...
String actualClass = servletClass;
Loader loader = getLoader();
// Acquire an instance of the class loader to be used
if (loader==null) {
throw new ServletException("No loader.");
}
ClassLoader classLoader = loader.getClassLoader();
if (classLoader!=null) {
classClass = classLoader.loadClass(actualClass);
// Instantiate and initialize an instance of the servlet class itself
servlet = (Servlet) classClass.newInstance();
// Call the initialization method of this servlet
servlet.init(null);
return servlet;
}· 如果该类仍然找不到，抛出 ClassNotFoundException 异常
public Class<?> loadClass(String name, boolean resolve)
throws ClassNotFoundException {
if (debug >= 2)
log("loadClass(" + name + ", " + resolve + ")");
Class<?> clazz = null;
// Don't load classes if class loader is stopped
if (!started) { //若webappclassloader没有启动....
log("Lifecycle error : CL stopped");
throw new ClassNotFoundException(name);
}
// (0) Check our previously loaded local class cache
clazz = findLoadedClass0(name); //看下面临时放进来的代码 等于是先在本地存储的已加载的类(hashmap)中找
if (clazz != null) {
if (debug >= 3)
log(" Returning class from cache");
if (resolve)
resolveClass(clazz);
return (clazz);
}
/*
protected Class<?> findLoadedClass0(String name) {
ResourceEntry entry = (ResourceEntry) resourceEntries.get(name);
if (entry != null) {
return entry.loadedClass;
}
return (null);
}
*/
// (0.1) Check our previously loaded class cache
clazz = findLoadedClass(name); //再去虚拟机中去找
if (clazz != null) {
if (debug >= 3)
log(" Returning class from cache");
if (resolve)
resolveClass(clazz);
return (clazz);
}
// (0.2) Try loading the class with the system class loader, to prevent
// the webapp from overriding J2SE classes
try {
//system 为系统类加载器 sun.misc.Launcher$AppClassLoader
//先用系统加载器加载
//为什么先用系统加载器 如果你写了一个类 全名为"java.lang.Object" 懂了吧?
//大家可能会想 系统加载器不是什么都能加载吗? 那还要后面的代码做什么?
//系统加载器的加载目录是什么 大家看看就明白了
clazz = system.loadClass(name);
if (clazz != null) {
if (resolve)
resolveClass(clazz);
return (clazz);
}
} catch (ClassNotFoundException e) {
// Ignore
}
//关于安全的问题 我没有研究过里面具体的代码
// (0.5) Permission to access this class when using a SecurityManager
if (securityManager != null) {
int i = name.lastIndexOf('.');
if (i >= 0) {
try {
securityManager.checkPackageAccess(name.substring(0,i));
} catch (SecurityException se) {
String error = "Security Violation, attempt to use " +
"Restricted Class: " + name;
System.out.println(error);
se.printStackTrace();
log(error);
throw new ClassNotFoundException(error);
}
}
}
//delegate默认为false
//filter 如果要加载的类是packageTrigers里面所限定的 就返回true
//书上说packageTrigers 里面的包是不允许载入的
//可代码里没有体现不能加载呀? 谁知道为什么,麻烦告知我一声
boolean delegateLoad = delegate || filter(name);
System.out.println(delegate+" "+filter(name)+" ddd");
// (1) Delegate to our parent if requested
if (delegateLoad) {
if (debug >= 3)
log(" Delegating to parent classloader");
ClassLoader loader = parent;
System.out.println(loader+" loader");
if (loader == null)
loader = system;
try {
clazz = loader.loadClass(name);
if (clazz != null) {
if (debug >= 3)
log(" Loading class from parent");
if (resolve)
resolveClass(clazz);
return (clazz);
}
} catch (ClassNotFoundException e) {
;
}
}
// (2) Search local repositories
//至于repositories属性 是在webappLoader类start方法里 setRepositories()设定的
//使用的各个方法如下
//findClass findClassInternal findResourceInternal
//在findResourceInternal中先加载WEB-INF/classes中的文件,然后加载WEB-INF/lib下的jar文件
//最后 resourceEntries.put(name, entry);
//会把加载的enety放入resourceEntries中缓存起来
if (debug >= 3)
log(" Searching local repositories");
try {
clazz = findClass(name);
if (clazz != null) {
if (debug >= 3)
log(" Loading class from local repository");
if (resolve)
resolveClass(clazz);
return (clazz);
}
} catch (ClassNotFoundException e) {
;
}
//系统加载器前面已经加载过来 如果程序能运行到这里就说明系统加载器不行 为什么还要再加载一遍
// (3) Delegate to parent unconditionally
if (!delegateLoad) {
if (debug >= 3)
log(" Delegating to parent classloader");
ClassLoader loader = parent;
if (loader == null)
loader = system;
try {
clazz = loader.loadClass(name);
if (clazz != null) {
if (debug >= 3)
log(" Loading class from parent");
if (resolve)
resolveClass(clazz);
return (clazz);
}
} catch (ClassNotFoundException e) {
;
}
}
// This class was not found
throw new ClassNotFoundException(name);
}Context context = new StandardContext();
// StandardContext's start method adds a default mapper
context.setPath("/myApp");
context.setDocBase("myApp");
标签：tomcat 源码 缓存 delegate security
原文地址：http://blog.csdn.net/dlf123321/article/details/40620265
