责任链设计模式

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 <b>模拟 Servlet 中的 Request 对象</b> * * @author jiang ru yi */ public class HttpServletRequest { private String requestContext; private Map<String, Object> requestParam = new HashMap<>(); public String getRequestContext() { return requestContext; } public void setRequestContext(String requestContext) { this.requestContext = requestContext; } public void setRequestParam(Map<String, Object> 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 <b>模拟 Servlet 中的 Response 对象</b> * * @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 <b>公用的过滤器抽象层</b> * * @author jiang ru yi */ public abstract class HttpFilter { public abstract void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain); }

过滤器调度

/** * @desc <b>过滤器的调度器</b> * * @author jiang ru yi */ public class FilterChain { private List<HttpFilter> 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("<EvE>, 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 <b>过滤请求中的危险符号( < > )</b> * * @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("<", "&le;").replaceAll(">", "&lt;"); request.setRequestContext(result); chain.doFilter(request, response); } }

抽象层子类 : 校验用户是否登录

/** * @desc <b>过滤用户是否登录</b> * * @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"); } } }