Java体系知识之过滤器Filter
1 技术简介
(1)过滤器：
净水器
空气净化器
...
(2)JavaWeb组件：
Servlet
Filter
Listener
(3)作用：
适合做一些通用的操作
A.普通意义的公共代码：
跨域请求处理；
字符编码；
B.逻辑方面的公共代码：
登录访问控制：根据是否登录判断
若已登录过，可允许继续访问；
若未登录，不允许继续访问；
权限访问控制：根据是否拥有权限判断
若已拥有权限，可允许访问；
若不拥有权限，不允许访问；
2 过滤器使用步骤（重点）
2.1 使用步骤
(1)创建一个类，实现Filter接口
(2)重写方法
(3)配置过滤器：
web.xml;
注解；
2.2 案例
package com.javasm.filter.basic;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;
@WebFilter("/demo01")
public class MyFilterDemo01 implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void destroy() {
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("执行MyFilterDemo01.doFilter()");
}
}
3 过滤器执行过程（重点）
3.1 内容概述
(1)当请求过来时，先进入过滤器执行
(2)若过滤器有放行代码，再找对应的Servlet执行
(3)最后执行放行代码下面的语句
3.2 案例
package com.javasm.filter.basic;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;
@WebFilter("/demo02")
public class MyFilterDemo02 implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void destroy() {
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("执行MyFilterDemo02.doFilter()");
filterChain.doFilter(servletRequest,servletResponse);
System.out.println("执行MyFilterDemo02过滤器放行代码下面的语句");
}
}
4 过滤器生命周期
4.1 内容概述
(1)服务器启动时，创建Filter实例，触发init方法执行
(2)当有请求访问时，执行doFilter方法
(3)服务器正常关闭时，销毁Filter实例，触发destroy方法执行
4.2 案例
package com.javasm.filter.basic;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import java.io.IOException;
@WebFilter("/demo03")
public class MyFilterDemo03 implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("服务器启动时，创建Filter实例，触发init方法执行");
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("执行MyFilterDemo03.doFilter()");
}
@Override
public void destroy() {
System.out.println("服务器正常关闭时，销毁Filter实例，触发destroy方法执行");
}
}
5 过滤器配置详解
5.1 内容概述
(1)拦截具体资源：比如 /demo04
(2)拦截指定目录：比如 /menu
6 过滤器链
(1)当经过分析，发现该案例中需要使用多个过滤器时，则配置多个多滤器即可
(2)当给多个过滤器配置相同的访问路径后，执行顺序：
注解配置：按照类名的字符串比较规则比较，值小的先执行；
web.xml：哪个过滤器的配置代码在前面，先执行哪个过滤器；
7 综合案例（重点）
7.1 处理请求数据乱码
7.1.1 MyFilter1
package com.javasm.filter.case1;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebFilter("/*")
public class MyFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void destroy() {
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
servletRequest.setCharacterEncoding("utf-8");
filterChain.doFilter(servletRequest,servletResponse);
}
}
7.2 登录访问控制&权限访问控制
(1)场景：
用户执行登录->访问其他模块
问题：
未登录->不能访问其他模块 给用户设置提示信息
无权限->不能访问对应模块 给用户设置提示信息
(2)过滤器：
未登录->不能访问其他模块 给用户设置提示信息
无权限->不能访问对应模块 给用户设置提示信息
(3)过程：
模拟：
filter
servlet：假设用户登录成功，设置基础用户数据和用户权限数据绑定到session对象
7.2.1 案例实现
7.2.1 MyFilter1
package com.javasm.filter.case2.filter;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebFilter("/*")
public class MyFilter1 implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void destroy() {
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
System.out.println("1111");
HttpServletRequest req = (HttpServletRequest) servletRequest;
HttpServletResponse resp = (HttpServletResponse) servletResponse;
servletRequest.setCharacterEncoding("utf-8");
String requestURI = req.getRequestURI();
if("/login".equals(requestURI) || requestURI.endsWith(".html")){
filterChain.doFilter(servletRequest,servletResponse);
}
}
}
7.2.2 MyFilter2
package com.javasm.filter.case2.filter;
import com.alibaba.fastjson.JSON;
import com.javasm.filter.entity.CodeAndMsg;
import com.javasm.filter.entity.ReturnEntity;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;
@WebFilter("/*")
public class MyFilter2 implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void destroy() {
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) servletRequest;
HttpServletResponse resp = (HttpServletResponse) servletResponse;
HttpSession session = req.getSession();
String userName = (String) session.getAttribute("userName");
String requestURI = req.getRequestURI();
if ("/login".equals(requestURI) || requestURI.endsWith(".html")) {
filterChain.doFilter(servletRequest, servletResponse);
} else {
if (userName != null) {
filterChain.doFilter(servletRequest, servletResponse);
} else {
ReturnEntity re = new ReturnEntity();
re.setReturnCode(CodeAndMsg.NO_LOGIN.getReturnCode());
re.setReturnMsg(CodeAndMsg.NO_LOGIN.getReturnMsg());
resp.setContentType("application/json;charset=utf-8");
PrintWriter writer = resp.getWriter();
writer.print(JSON.toJSONString(re));
writer.flush();
writer.close();
}
}
}
}
7.2.3 MyFilter3
package com.javasm.filter.case2.filter;
import com.alibaba.fastjson.JSON;
import com.javasm.filter.entity.CodeAndMsg;
import com.javasm.filter.entity.ReturnEntity;
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;
@WebFilter("/*")
public class MyFilter3 implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void destroy() {
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) servletRequest;
HttpServletResponse resp = (HttpServletResponse) servletResponse;
HttpSession session = req.getSession();
List<String> authList = (List<String>) session.getAttribute("authList");
String requestURI = req.getRequestURI();
if ("/login".equals(requestURI)) {
filterChain.doFilter(servletRequest, servletResponse);
} else {
if(authList.contains(requestURI)){
filterChain.doFilter(servletRequest, servletResponse);
}else{
ReturnEntity re = new ReturnEntity();
re.setReturnCode(CodeAndMsg.NO_AUTH.getReturnCode());
re.setReturnMsg(CodeAndMsg.NO_AUTH.getReturnMsg());
resp.setContentType("application/json;charset=utf-8");
PrintWriter writer = resp.getWriter();
writer.print(JSON.toJSONString(re));
writer.flush();
writer.close();
}
}
}
}
7.2.4 LoginServlet
package com.javasm.filter.case2.servlet;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
@WebServlet("/login")
public class LoginServlet extends HttpServlet {
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println(req.getParameter("userName"));
boolean isLogin = true;
if (isLogin) {
HttpSession session = req.getSession();
session.setAttribute("userName", "tom");
List<String> authList = new ArrayList<>();
authList.add("/menu/query");
authList.add("/menu/queryOneMenu");
session.setAttribute("authList", authList);
}
}
}
