spring源码分析之resource

Resource相关类图

看代码过程中觉得很好的地方

AbstractResource.java

publicbooleanexists() {

// Try file existence: can we find the file in the file system? try {

return getFile().exists();

}

catch (IOException ex) {

// Fall back to stream existence: can we open the stream? try {

InputStream is = getInputStream(); is.close(); returntrue;

}

catch (Throwable isEx) { returnfalse; } } }

这段代码，面向接口编程的典范，getInputStream()是父接口定义的方法，实际上的实现是在AbstractResource的子类中实现。以一种类似于模板方法模式的方式去编程，未来可扩展性较高。

AbstractFileResolvingResource.java

/**

* Inner delegate class, avoiding a hard JBoss VFS API dependency at runtime. */

privatestaticclassVfsResourceDelegate{

publicstatic Resource getResource(URL url) throws IOException { returnnew VfsResource(VfsUtils.getRoot(url)); }

publicstatic Resource getResource(URI uri) throws IOException {

returnnew VfsResource(VfsUtils.getRoot(uri)); } }

看上面的代码的注释，目的是防止在运行时对JBoss VFS API的强依赖。说白了还是要反向依赖，依赖注入。单独看这段代码是看不出如何做到的，仔细看VfsUtils里面的代码，如下：

protectedstatic Object getRoot(URL url) throws IOException {

return invokeVfsMethod(VFS_METHOD_GET_ROOT_URL, null, url); }

// 反射调用方法

protectedstatic Object invokeVfsMethod(Method method, Object target, Object... args) throws IOException { try {

return method.invoke(target, args); }

catch (InvocationTargetException ex) {

Throwable targetEx = ex.getTargetException(); if (targetEx instanceof IOException) { throw (IOException) targetEx; }

ReflectionUtils.handleInvocationTargetException(ex); }

catch (Exception ex) {

ReflectionUtils.handleReflectionException(ex); }

thrownew IllegalStateException(\code path reached\); }

invokeVfsMethod里的method的定义如下：

// 定义静态成员变量method

privatestatic Method VFS_METHOD_GET_ROOT_URL = null; privatestatic Method VFS_METHOD_GET_ROOT_URI = null; privatestaticfinal String VFS3_PKG = \; privatestaticfinal String VFS_NAME = \;

// 通过classLoader获取类