Filter和FilterChain的关系咋看之下，是FilterChain中包含一个List<Filter>，然后去遍历List来执行所有的Filter。真的是图样图森破。
先装个逼，贴个源码：
/**
* A filter is an object that performs filtering tasks on either the request to
* a resource (a servlet or static content), or on the response from a resource,
* or both.
* Filters perform filtering in the <code>doFilter</code> method.
* @since Servlet 2.3
*/
public interface Filter {
public void init(FilterConfig filterConfig) throws ServletException;
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException;
public void destroy();
}
/**
* A FilterChain is an object provided by the servlet container to the developer
* giving a view into the invocation chain of a filtered request for a resource.
* Filters use the FilterChain to invoke the next filter in the chain, or if the
* calling filter is the last filter in the chain, to invoke the resource at the
* end of the chain.
**/
public interface FilterChain {
/**
* Causes the next filter in the chain to be invoked, or if the calling
* filter is the last filter in the chain, causes the resource at the end of
* the chain to be invoked.
*/
public void doFilter(ServletRequest request, ServletResponse response)
throws IOException, ServletException;
}
说了一堆，大概意思总结一下：Filter用来执行过滤任务。FilterChain用来查看资源过滤请求的调用链。Filter通过FilterChain来调用过滤链中的下一个Filter，如果当前执行的Filter是过滤链中的最后一个，则可以继续调用资源。一脸懵逼，这是什么实现逻辑。先来看看下面这段代码的逻辑：
public class IAClass {
public void doSomething(IAChainClass chain) {
System.out.println("i am IAClass"+chain.position);
chain.doSomething();
}
static class IAChainClass {
List<IAClass> IAChains = new ArrayList<IAClass>();
public IAChainClass() {
IAChains.add(new IAClass());
IAChains.add(new IAClass());
IAChains.add(new IAClass());
}
int position = 0;
public void doSomething() {
if (position == IAChains.size()) {
System.out.println("end");
return;
}
IAClass ia = IAChains.get(position++);
ia.doSomething(this);
}
}
public static void main(String args[]){
new IAChainClass().doSomeThing();
}
}
打印结果是：
i am IAClass1
i am IAClass2
i am IAClass3
end
在IAChainClass中，如果当前节点不是过滤链中最后一个节点，则调用当前节点的doSomething()时，同时做两件事：1）将当前过滤器链继续传入过滤器，2）将过滤器链的当前节点后移一位；直到所有过滤器执行完成再退出。
