java 之 编码实现Filter学习示例

public interface Filter {void doFilter(Request request,Response response,FilterChain chain);}

public class HTMLFilter implements Filter {@Overridepublic void doFilter(Request request, Response response, FilterChain chain) {request.setRequestStr(request.getRequestStr().replace('<', '[').replace('>', ']'));chain.doFilter(request, response, chain);response.setResponseStr("-----------HtmlFilter()");}}

public class SensitiveFilter implements Filter {@Overridepublic void doFilter(Request request, Response response, FilterChain chain) {request.setRequestStr(request.getRequestStr().replace("s","js"));chain.doFilter(request, response, chain);response.setResponseStr("-----------SensitiveFilter()");}}

import java.util.ArrayList;import java.util.List;public class FilterChain implements Filter {List<Filter> filters = new ArrayList<Filter>();int index = 0;public FilterChain addFilter(Filter f) {this.filters.add(f);return this;}@Overridepublic void doFilter(Request request, Response response, FilterChain chain) {if(index==filters.size()) {return;}Filter f = filters.get(index);index++;f.doFilter(request, response, chain);}}

public class Request {private String requestStr;public String getRequestStr() {return requestStr;}public void setRequestStr(String requestStr) {this.requestStr = requestStr;}}

public class Response {private String responseStr="response";public String getResponseStr() {return responseStr;}public void setResponseStr(String responseStr) {this.responseStr += responseStr;}}

public class TestFilter {/** * @param args */public static void main(String[] args) {String msg = "<script>";Request request = new Request();request.setRequestStr(msg);Response response = new Response();FilterChain fc = new FilterChain();fc.addFilter(new HTMLFilter()).addFilter(new SensitiveFilter());fc.doFilter(request, response, fc);System.out.println(request.getRequestStr());System.out.println(response.getResponseStr());}}

打印结果：

[jscript]
response-----------SensitiveFilter()-----------HtmlFilter()

##########################################################################################

通常我们所访问的资源是一个servlet或jsp页面，而jsp其实是一个被封装了的servlet（每个jsp执行前都会被转化为一个标准的servlet，这点若还有不明白的请自己到网上查一下吧），于是我们就可以统一地认为我们每次访问的都是一个Servlet,而每当我们访问一个servlet时，web容器都会调用该Servlet的service方法去处理请求。而在service方法又会根据请求方式的不同（Get/Post）去调用相应的doGet()或doPost()方法，实际处理请求的就是这个doGet或doPost方法。写过servlet的朋友都应该知道，我们在doGet（或doPost）方法中是通过response.getWriter（）得到客户端的输出流对象，然后用此对象对客户进行响应。       到这里我们就应该理解了过滤器的执行流程了：执行第一个过滤器的chain.doFilter()之前的代码——>第二个过滤器的chain.doFilter()之前的代码——>……——>第n个过滤器的chain.doFilter()之前的代码——>所请求servlet的service()方法中的代码——>所请求servlet的doGet()或doPost()方法中的代码——>第n个过滤器的chain.doFilter()之后的代码——>……——>第二个过滤器的chain.doFilter()之后的代码——>第一个过滤器的chain.doFilter()之后的代码。