java设计模式-责任链

分析下Java web中的过滤器 、拦截器

过滤器：当用户请求（request）服务器时可以添加多个过滤器对请求进行过滤，

每个过滤器对请求有不同的过滤处理

多个过滤器就会形成一个过滤器链条

当过滤链条完成之后，server开始对请求处理

处理完成之后返回结果response

response还会逆序被过滤链条处理

完成之后返回用户 如下图：

代码部分：

请求与返回对象
public class Request {
	public  String RequestString;
}

public class Response {
	public  String ResponseString;
}

//过滤接口
public interface Filter {

	public void doFilter(Request request , Response response , FilterChain chain);
}
过滤实现类
public class HtmlFilter implements Filter{

	@Override
	public void doFilter(Request request, Response response, FilterChain chain) {
		request.RequestString = request.RequestString.replace("<", "[").replace(">", "]");
		System.out.println("HtmlFilter  request 处理完成 request.RequestString = "+request.RequestString);
		chain.doFilter(request, response, chain);
		response.ResponseString = response.ResponseString + "  |HtmlFilter response 处理";
		System.out.println("HtmlFilter  response 返回处理完成 response.ResponseString = "+response.ResponseString);

	}
}

public class SensitiveFilter implements Filter{

	@Override
	public void doFilter(Request request, Response response, FilterChain chain) {
		request.RequestString = request.RequestString.replace("敏感", "**");
		System.out.println("SensitiveFilter  request 处理完成 request.RequestString = "+request.RequestString);
		chain.doFilter(request, response, chain);
		response.ResponseString = response.ResponseString + "  | SensitiveFilter response 处理 ";
		System.out.println("SensitiveFilter  response 返回处理完成 response.ResponseString = "+response.ResponseString);
	}
}

过滤链条
public class FilterChain {

	private List<Filter> filters = new ArrayList<Filter>();

	public FilterChain addFilter(Filter filter){
		filters.add(filter);
		return this;
	}

	int index = -1;

	public void doFilter(Request request,Response response , FilterChain chain){
		if(filters.size() > ++ index){
			filters.get(index).doFilter(request, response, chain);
		}else if(filters.size() ==  index){
			response.ResponseString = "【server处理代码部分】";
			System.out.println("业务逻辑处理之后的返回:" + response.ResponseString);
		}
	}

}

测试类
public class MainTest {

	public static void main(String[] args) {
		Request req = new Request();
		req.RequestString = "O(∩_∩)O哈哈~ <script>  <style> 我是敏感词";
		Response res = new Response();
		FilterChain chain = new FilterChain();
		chain.addFilter(new HtmlFilter())
				 .addFilter(new SensitiveFilter());
		chain.doFilter(req, res, chain);
	}
}

执行结果
HtmlFilter  request 处理完成 request.RequestString = O(∩_∩)O哈哈~ [script]  [style] 我是敏感词
SensitiveFilter  request 处理完成 request.RequestString = O(∩_∩)O哈哈~ [script]  [style] 我是**词
业务逻辑处理之后的返回:【server处理代码部分】
SensitiveFilter  response 返回处理完成 response.ResponseString = 【server处理代码部分】  | SensitiveFilter response 处理
HtmlFilter  response 返回处理完成 response.ResponseString = 【server处理代码部分】  | SensitiveFilter response 处理   |HtmlFilter response 处理

小结：请求 ——>htmlFilter过滤——>sensitiveFilter过滤——>server处理返回response——>sensitiveFilter处理——>htmlFilter处理

问题：如果遇到一些非法请求需要直接返回该如果做

代码如下：

添加非法过滤类
public class ErrorFilter implements Filter{

	@Override
	public void doFilter(Request request, Response response, FilterChain chain) {
		request.RequestString = request.RequestString.replace("(:", "^-_-^");
		System.out.println("ErrorFilter  request 处理完成 request.RequestString = "+request.RequestString);
		System.out.println("**********在这里出错拦截返回**********");
		boolean flag = false;
		//模拟错误请求
		if(flag){
			chain.doFilter(request, response, chain);
		}
		System.out.println("**********在这里出错拦截返回**********");
		response.ResponseString = response.ResponseString + "  |ErrorFilter response 处理";
		System.out.println("ErrorFilter  response 返回处理完成 response.ResponseString = "+response.ResponseString);
	}
}
修改测试代码
将错误过滤器放在html  与  sensitive之间
public class MainTest {

	public static void main(String[] args) {
		Request req = new Request();
		req.RequestString = "O(∩_∩)O哈哈~ <script>  <style> 我是敏感词";
		Response res = new Response();
		FilterChain chain = new FilterChain();
		chain.addFilter(new HtmlFilter())
				  .addFilter(new ErrorFilter())
				 .addFilter(new SensitiveFilter());
		chain.doFilter(req, res, chain);
	}
}
执行结果
HtmlFilter  request 处理完成 request.RequestString = O(∩_∩)O哈哈~ [script]  [style] 我是敏感词
ErrorFilter  request 处理完成 request.RequestString = O(∩_∩)O哈哈~ [script]  [style] 我是敏感词
**********在这里出错拦截返回**********
**********在这里出错拦截返回**********
ErrorFilter  response 返回处理完成 response.ResponseString = null  |ErrorFilter response 处理
HtmlFilter  response 返回处理完成 response.ResponseString = null  |ErrorFilter response 处理  |HtmlFilter response 处理

看以看到response返回结果中的Null值
该值代表没有经过server直接返回
而且也没有经过sensitiveFilter处理

总结：

在过滤器中如果遇到非法请求 需要直接返回 则不需要调用chain.doFilter() 函数  请求会直接返回.