使用过滤器处理404错误获得指定资源。

  在项目中我遇到读取资源问题，资源路径没有规则，还有很多虚拟路径处理。我使用了Filter过滤404错误方法处理这些资源。在实现过程中统一了资源处理方法，并且容易同spring的整合。该实现在Tomcat 9.0上测试通过。

  实现需要注意二点：

1. 使用HttpServletResponseWrapper包装response
2. 覆盖sendError方法，遇到404错误不能触发错，如触发错误response就被托管，托管后就不能输出数据。

  下面是 Error404ResponseWrapper 具体实现：

package com.filter;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpServletResponseWrapper;import java.io.IOException;/** * Created by TYK on 2017/9/23. */public class Error404ResponseWrapper extends HttpServletResponseWrapper {    private int status = SC_OK;    public Error404ResponseWrapper(Error404Filter error404Filter, HttpServletResponse response) {        super(response);    }    @Override    public void sendError(int sc) throws IOException {        this.status = sc;        if (isFound()) {            super.sendError(sc);        } else {            super.setStatus(SC_OK);        }    }    @Override    public void sendError(int sc, String msg) throws IOException {        this.status = sc;        if (isFound()) {            super.sendError(sc, msg);        } else {            super.setStatus(SC_OK);        }    }    public void setStatus(int status) {        this.status = status;        super.setStatus(status);    }    @Override    public void reset() {        this.status = SC_OK;        super.reset();    }    public boolean isFound() {        return status != SC_NOT_FOUND;    }}

  注意sendError处理，上面代码解决了核心两个问题。接下来完成过滤就可。
  下面是 Error404Filter 具体实现：

package com.filter;import javax.servlet.*;import javax.servlet.annotation.WebFilter;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;/** * Created by TYK on 2017/9/24. */public class Error404Filter implements Filter {    public void destroy() {    }    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws ServletException, IOException {        HttpServletRequest request = (HttpServletRequest) req;        HttpServletResponse response = (HttpServletResponse) resp;        Error404ResponseWrapper responseWrapper = new Error404ResponseWrapper(this, response);        chain.doFilter(request, responseWrapper);        if (responseWrapper.isFound()) {            return;        }        response.sendRedirect("404.html");    }    public void init(FilterConfig config) throws ServletException {    }}

  web.xml配置

    <filter>        <filter-name>Error404Filter</filter-name>        <filter-class>com.filter.Error404Filter</filter-class>    </filter> <!--404-->    <filter-mapping>        <filter-name>Error404Filter</filter-name>        <url-pattern>/*</url-pattern>    </filter-mapping>

  注意：在web.xml中把该过滤器放在所有过滤器后。

  原文地址