责任链的应用场景

• Servlet API 中的 Filter 过滤器
• MVC 框架中的拦截器
• . . .

简单使用责任链模式拆分 Servlet API 中的过滤器

模拟 Servlet 中的 Request 对象

/** * @desc 模拟 Servlet 中的 Request 对象 *  * @author jiang ru yi */public class HttpServletRequest {    private String requestContext;    private Map
    
      requestParam = new HashMap<>();    public String getRequestContext() {        return requestContext;    }    public void setRequestContext(String requestContext) {        this.requestContext = requestContext;    }    public void setRequestParam(Map
     
       requestParam) {        this.requestParam = requestParam;    }        public Object setAttribute(String key, Object value) {        return requestParam.put(key, value);    }        public Object getAttribute(String key) {        return requestParam.get(key);    }        public Object removeAttribute(String key) {        return requestParam.remove(key);    }    }
     
    

模拟 Servlet 中的 Response 对象

/** * @desc 模拟 Servlet 中的 Response 对象 *  * @author jiang ru yi */public class HttpServletResponse {    private String responseContext;    public String getResponseContext() {        return responseContext;    }    public void setResponseContext(String responseContext) {        this.responseContext = responseContext;    }}

过滤器抽象层

/** * @desc 公用的过滤器抽象层 *  * @author jiang ru yi */public abstract class HttpFilter {        public abstract void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain);}

过滤器调度

/** * @desc 过滤器的调度器 *  * @author jiang ru yi */public class FilterChain {    private List
    
      filters = new ArrayList<>();    private int currFilter;    public boolean addFilter(HttpFilter filter) {        return filters.add(filter);    }        public boolean removeFilter(HttpFilter filter) {        return filters.remove(filter);    }        public void doFilter(HttpServletRequest request, HttpServletResponse response) {        if (currFilter++ == filters.size()) return;                filters.get(currFilter - 1).doFilter(request, response, this);    }}
    

Junit 测试

public static void main(String[] args) {    HttpServletRequest request = new HttpServletRequest();    request.setRequestContext("
    
     , Y(OvO)Y");    request.setAttribute("user", "administrator");    HttpServletResponse response = new HttpServletResponse();    FilterChain chain = new FilterChain();    chain.addFilter(new CharacterSetFilter());    chain.addFilter(new PowerFilter());    chain.doFilter(request, response);    System.out.println(request.getRequestContext());}
    

抽象层子类 : 字符过滤器

/** * @desc 过滤请求中的危险符号( < > ) *  * @author jiang ru yi */public class CharacterSetFilter extends HttpFilter {    @Override    public void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain) {        String context = request.getRequestContext();        String result = context.replaceAll("<", "≤").replaceAll(">", "<");        request.setRequestContext(result);        chain.doFilter(request, response);    }}

抽象层子类 : 校验用户是否登录

/** * @desc 过滤用户是否登录 *  * @author jiang ru yi */public class PowerFilter extends HttpFilter {    @Override    public void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain) {        Object attribute = request.getAttribute("user");        if (null != attribute) {            chain.doFilter(request, response);        } else {            throw new RuntimeException("user not login");        }    }}