Spring Boot中filter的使用详解及原理( 二 ) 作者|SUPERUSR来源|urlify.cn/nIrqy

我们也可以在print("before:" + response)和print("after:" + response)这两个地方打上断点，然后调试一下，你会发现在before那里的response里是什么都么有的，而在after那里的response里则是已经有了test1字符串，也就是说controller类test1方法的返回值已经添加进了response ，所以如果你想对请求的response做一下过滤处理，那么一定要在chain.doFilter(res, rep)之后写你的逻辑。
接下来讲一下这个Filter和FilterChain都是怎么用责任链模式实现的，如果不太需要了解原理的话，往下的部分就可以不看了。。。好了，我们来模拟一下简单的实现SpringBoot中的Filter接口和FilterChain类：
首先是我们自己写的Filter接口，里边就一个doFilter方法：
package filterchain_pattern;public interface Filter {public void doFilter(Request request, Response response, FilterChain chain);}接下来是我们自己写的FilterChain类：
package filterchain_pattern;import java.util.ArrayList; import java.util.List;public class FilterChain implements Filter {private List filters = new ArrayList<>(); int index = 0;public FilterChain addFilter(Filter filter) { filters.add(filter); return this; }@Override public void doFilter(Request request, Response response, FilterChain chain) {if(index == filters.size()) { return; } Filter filter = filters.get(index); index++; filter.doFilter(request, response, chain); }}接下来模拟Request类和Response类：
package filterchain_pattern;public class Request {public String requestStr;}package filterchain_pattern;public class Response {public String responseStr;}然后我们下一个Filter接口的实现类HTMLFilter类，该类会将requestStr中的<>替换成[] ，并给responseStr添加------------HTML response filter字符串，并在控制台打印出来：
package filterchain_pattern;public class HTMLFilter implements Filter {@Override public void doFilter(Request request, Response response, FilterChain chain) { request.requestStr = request.requestStr.replace("<", "[").replace(">", "]") + "--------HTML Request Filter"; System.out.println("HTML Filter request Str:" + request.requestStr); chain.doFilter(request, response, chain); response.responseStr = response.responseStr + "-------------HTML response filter"; System.out.println("HTML Filter response Str:" + response.responseStr); } }然后是另外一个Filter接口的实现类SensitiveFilter类，该类会给requestStr添加一段字符串，给responseStr添加一段字符串，并在控制台打印出来：
package filterchain_pattern;public class SensitiveFilter implements Filter {@Override public void doFilter(Request request, Response response, FilterChain chain) { request.requestStr = request.requestStr + "---------------Sensitive request Filter"; System.out.println("sensitiveFilter request str:" + request.requestStr); chain.doFilter(request, response, chain); response.responseStr = response.responseStr + "---------------------sensitive response filter"; System.out.println("sensitiveFilter response str:" + response.responseStr); }}最后使我们的Main方法类：
package filterchain_pattern;public class MainTest {public static void main(String[] args) {String msg = "testMsg"; Request request = new Request(); request.requestStr = msg; Response response = new Response(); response.responseStr = "responseStr";FilterChain fc = new FilterChain(); fc.addFilter(new HTMLFilter()).addFilter(new SensitiveFilter()); fc.doFilter(request, response, fc);}}打印结果如下，这就是责任链模式的实际应用了：
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