Java学习路线-49：Servlet过滤器Filter

课时1 过滤器的入门

JavaWeb三大组件
1、都需要在web.xml中进行配置
Servlet
Filter
Listener

2、过滤器
会在一组资源（jsp, servlet, css, html等等）的前面执行
可以让请求得到目标资源，也可以不让请求达到
过滤器有拦截请求的能力

3、编写过滤器
（1）实现Filter接口
（2）在web.xml中进行配置
（3）Filter是单例的

4、配置web.xml

<web-app>
    <filter>
        <filter-name>FilerName</filter-name>
        <filter-class>FilerClass</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>FilerName</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
</web-app>

继承示例

package com.pengshiyu.filtrer;

import javax.servlet.*;
import java.io.IOException;

public class Afilter implements Filter {
    /**
     * 创建之后马上执行，用来做初始化
     */
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    /**
     * 每次过滤都会执行
     */
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, 
        FilterChain filterChain) throws IOException, ServletException {
        System.out.println("进入过滤器");
        // 调用后序方法
        filterChain.doFilter(servletRequest, servletResponse);
        System.out.println("离开过滤器");
    }

    /**
     * 销毁之前的调用，用来释放资源
     */
    @Override
    public void destroy() {

    }
}

FilterConfig -> 与ServletConfig相似
获取初始化参数 getInitParameter()
获取过滤器名称 getFilterName()
获取application getServletContext()

FilterChain
放行,执行后序方法 doFilter()

课时2 多个过滤器的执行顺序

执行下一个过滤器或目标资源
FilterChain.doFilter()

Afilter进入过滤器
Bfilter进入过滤器
getAge
Bfilter离开过滤器
Afilter离开过滤器

课时3 四种拦截方式

请求 REQUEST 默认
转发 FORWARD
包含 INCLUDE
错误 ERROR

<filter-mapping>
    <filter-name>FilerName</filter-name>
    <url-pattern>/*</url-pattern>
    <dispatcher>REQUEST</dispatcher>
</filter-mapping>

页面出错

<error-page>
    <error-code>500</error-code>
    <location>500.html</location>
</error-page>

课时4 使用filter-mapping控制多个Filter的执行顺序

filter-mapping的配置顺序决定过滤器执行顺序

课时5 Filter的应用场景、Filter的目标资源、小结

预处理：执行目标资源之前做预处理工作，例如设置编码
拦截：通过条件判断是否放行，例如用户登录校验
回程拦截：目标资源执行之后，做一些后序的特殊处理工作，例如目标资源输出的数据进行处理

直接指定servlet-name

<filter-mapping>
    <filter-name>FilerName</filter-name>
    <servlet-name>ServletName</servlet-name>
</filter-mapping>

小结
Filter3个方法
FilterChain类
4中拦截方式

课时6 案例1：分IP统计访问次数

数据结构：

ip	count
192.168.0.1	32
192.168.0.2	22

统计工作在所有资源之前都执行，使用Filter
这个过滤器只做统计，不做拦截
数据Map<String, Integer>
Map保存到ServletContext中
从request中获取客户端ip

使用监听器创建 map
AListener.java

package com.pengshiyu.listener;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import java.util.LinkedHashMap;
import java.util.Map;

public class AListener implements ServletContextListener {
    // 服务器启动时创建map
    public void contextInitialized(ServletContextEvent sce) {
        Map<String, Integer> map = new LinkedHashMap<String, Integer>();
        sce.getServletContext().setAttribute("map", map);
    }

    public void contextDestroyed(ServletContextEvent sce) {
    }
}

使用过滤器统计数据
AFilter.java

package com.pengshiyu.filter;

import javax.servlet.*;
import java.io.IOException;
import java.util.Map;

public class AFilter implements Filter {
    private FilterConfig config;

    /**
     * 创建之后马上执行，用来做初始化
     */
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        this.config = filterConfig;
    }

    /**
     * 每次过滤都会执行
     */
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, 
        FilterChain filterChain) throws IOException, ServletException {
        ServletContext app = this.config.getServletContext();
        Map<String, Integer> map = (Map<String, Integer>)app.getAttribute("map");

        String ip  =  request.getRemoteAddr();
        System.out.println("ip: " + ip);

        if(map.containsKey(ip)){
            Integer count = map.get(ip);
            map.put(ip, count+1);
        } else{
            map.put(ip, 1);
        }

        // 放行
        filterChain.doFilter(request, response);

    }

    /**
     * 销毁之前的调用，用来释放资源
     */
    @Override
    public void destroy() {

    }
}

显示数据
BServlet.java

package com.pengshiyu.servlet;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Map;

public class BServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) 
    throws IOException {
        ServletContext app = getServletContext();
        Map<String, Integer> map = (Map<String, Integer>) app.getAttribute("map");
        
        response.setContentType("text/html; charset=UTF-8");
        response.getWriter().println(map.toString());

    }
}

配置监听器和过滤器生效
web.xml

<?xml version="1.0" encoding="utf-8"?>

<web-app>
    <servlet>
        <servlet-name>BServlet</servlet-name>
        <servlet-class>com.pengshiyu.servlet.BServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>BServlet</servlet-name>
        <url-pattern>/b</url-pattern>
    </servlet-mapping>

    <filter>
        <filter-name>AFilter</filter-name>
        <filter-class>com.pengshiyu.filter.AFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>AFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

    <listener>
        <listener-class>com.pengshiyu.listener.AListener</listener-class>
    </listener>
</web-app>

课时7 案例2：粗粒度权限管理

基于角色的权限控制RBAC
tb_user
tb_role
tb_userrole
tb_menu
tb_rolemenu

web.xml

<?xml version="1.0" encoding="utf-8"?>

<web-app>
    <servlet>
        <servlet-name>AServlet</servlet-name>
        <servlet-class>com.pengshiyu.servlet.AServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>AServlet</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>

    <filter>
        <filter-name>AFilter</filter-name>
        <filter-class>com.pengshiyu.filter.AFilter</filter-class>
    </filter>
    <filter-mapping>
<!--        不能将过滤器设置在login.html上，不然没法登录了-->
        <filter-name>AFilter</filter-name>
        <url-pattern>/hello.html</url-pattern>
    </filter-mapping>

</web-app>

AServlet.java

package com.pengshiyu.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class AServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) 
    throws ServletException, IOException {
        String username = request.getParameter("username");
        System.out.println("post: " + username);
        // 设置session
        request.getSession().setAttribute("username", username);
        // 跳转页面
        request.getRequestDispatcher("hello.html").forward(request, response);
    }
}

过滤器进行简单的权限校验
AFilter.java

package com.pengshiyu.filter;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;

public class AFilter implements Filter {
    private FilterConfig config;
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        this.config = filterConfig;
    }

    @Override
    public void doFilter(ServletRequest req, ServletResponse response, 
        FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest)req;

        String username = (String) request.getSession().getAttribute("username");
        System.out.println("filter: " + username);

        if(username != null){
            // 放行
            filterChain.doFilter(request, response);
        } else{
            // 跳转到登录页
            request.getRequestDispatcher("login.html").forward(request, response);
        }
    }

    @Override
    public void destroy() {

    }
}

课时8 案例3：全站编码问题

// post编码
request.setCharacterEncoding("utf-8");

// get编码
String username = request.getParameter("username");
username = new String(username.getBytes(StandardCharsets.ISO_8859_1), StandardCharsets.UTF_8);

// 响应编码
response.setContentType("text/html; charset=UTF-8");

HttpServletRequest装饰类
EncodingRequest.java

package com.pengshiyu.filter;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import java.nio.charset.StandardCharsets;

// 装饰器
public class EncodingRequest extends HttpServletRequestWrapper {

    public EncodingRequest(HttpServletRequest request) {
        super(request);
    }

    @Override
    public String getParameter(String name) {
        // 处理编码问题
        String value = super.getParameter(name);
        value = new String(value.getBytes(StandardCharsets.ISO_8859_1), StandardCharsets.UTF_8);
        return value;

    }
}

过滤器AFilter.java

package com.pengshiyu.filter;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;

public class AFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, 
        FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest httpServletRequest = (HttpServletRequest) request;
        String method = httpServletRequest.getMethod();

        // 设置响应编码
        response.setContentType("text/html; charset=UTF-8");

        if ("GET".equals(method)) {
            // 放行
            EncodingRequest encodingRequest = new EncodingRequest(httpServletRequest);
            filterChain.doFilter(encodingRequest, response);
        } else if ("POST".equals(method)) {
            request.setCharacterEncoding("utf-8");
            filterChain.doFilter(request, response);
        }
    }

    @Override
    public void destroy() {

    }
}

响应处理AServlet.java

package com.pengshiyu.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class AServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) 
    throws ServletException, IOException {
        System.out.println(request.getParameter("name"));
        response.getWriter().print("你好");
    }
}

web.xml

<?xml version="1.0" encoding="utf-8"?>

<web-app>
    <!-- 注册 Servlet，帮助web服务器反射该类 -->
    <servlet>
        <servlet-name>AServlet</servlet-name>
        <servlet-class>com.pengshiyu.servlet.AServlet</servlet-class>
    </servlet>
    <!-- 映射 Servlet 资源，用url-pattern元素标示 URL -->
    <servlet-mapping>
        <servlet-name>AServlet</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>

    <filter>
        <filter-name>AFilter</filter-name>
        <filter-class>com.pengshiyu.filter.AFilter</filter-class>
    </filter>
    <filter-mapping>
<!--        不能将过滤器设置在login.html上，不然没法登录了-->
        <filter-name>AFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
</web-app>

课时9 案例4：页面静态化之准备工作（图书管理小项目）

功能：
查询所有
按分类查看

BookServlet
    findAll()       查询全部
    findByCategory() 按分类查询

BookService: 省略

BookDao:
    List<Book> findAll()
    List<Book> findByCategory()

Book：
    bid
    bname
    price
    category

静态化：
第一次访问从数据库取数据，保存到html中
第二次之后访问就直接从html中读取，不再从数据库中取数据

数据准备：

create table tb_book(
    bid int primary key auto_increment,
    bname varchar(50),
    price decimal(10, 2),
    category int
);

insert into tb_book(bname, price, category) values("Java", 12, 1);
insert into tb_book(bname, price, category) values("Python", 12, 1);
insert into tb_book(bname, price, category) values("JavaScript", 12, 1);
insert into tb_book(bname, price, category) values("Go", 12, 1);

insert into tb_book(bname, price, category) values("三国演义", 12, 2);
insert into tb_book(bname, price, category) values("西游记", 12, 2);
insert into tb_book(bname, price, category) values("水浒传", 12, 2);
insert into tb_book(bname, price, category) values("红楼梦", 12, 2);

创建对应的Book类

package com.pengshiyu.bean;

public class Book {
    private int bid;
    private String bname;
    private double price;
    private int category;

    public Book() {
    }

    public int getBid() {
        return bid;
    }

    public void setBid(int bid) {
        this.bid = bid;
    }

    public String getBname() {
        return bname;
    }

    public void setBname(String bname) {
        this.bname = bname;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public int getCategory() {
        return category;
    }

    public void setCategory(int category) {
        this.category = category;
    }

    @Override
    public String toString() {
        return "Book{" +
                "bid=" + bid +
                ", bname='" + bname + '\'' +
                ", price=" + price +
                ", category=" + category +
                '}';
    }
}

BookDao.java

package com.pengshiyu.dao;

import com.pengshiyu.bean.Book;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import util.TxQueryRunner;

import java.sql.SQLException;
import java.util.List;

public class BookDao {
    private QueryRunner qr = new TxQueryRunner();

    public  List<Book> findAll() {
        String sql = "select * from tb_book";

        try {
            List<Book> list = qr.query(sql, new BeanListHandler<Book>(Book.class));
            System.out.println(list);
            return list;
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }

    public  List<Book> findByCategory(int category) {
        String sql = "select * from tb_book where category = ?";

        try {
            return qr.query(sql, new BeanListHandler<Book>(Book.class), category);
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }
}

BookServlet

package com.pengshiyu.servlet;

import com.pengshiyu.dao.BookDao;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class BookServlet extends BaseServlet {
    private BookDao bookDao = new BookDao();

    public void findAll(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
        request.setAttribute("bookList", bookDao.findAll());
        request.getRequestDispatcher("book.jsp").forward(request, response);
    }

    public void findByCategory(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int category = Integer.parseInt(request.getParameter("category"));
        request.setAttribute("bookList", bookDao.findByCategory(category));
        request.getRequestDispatcher("book.jsp").forward(request, response);

    }
}

用到的工具类 TxQueryRunner.java

package util;

import java.sql.Connection;
import java.sql.SQLException;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.ResultSetHandler;

public class TxQueryRunner extends QueryRunner {

    @Override
    public int[] batch(String sql, Object[][] params) throws SQLException {
        Connection con = JdbcUtil.getConnection();
        int[] result = super.batch(con, sql, params);
        JdbcUtil.releaseConnection(con);
        return result;
    }

    @Override
    public <T> T query(String sql, ResultSetHandler<T> rsh, Object... params)
            throws SQLException {
        Connection con = JdbcUtil.getConnection();
        T result = super.query(con, sql, rsh, params);
        JdbcUtil.releaseConnection(con);
        return result;
    }

    @Override
    public <T> T query(String sql, ResultSetHandler<T> rsh) throws SQLException {
        Connection con = JdbcUtil.getConnection();
        T result = super.query(con, sql, rsh);
        JdbcUtil.releaseConnection(con);
        return result;
    }

    @Override
    public int update(String sql) throws SQLException {
        Connection con = JdbcUtil.getConnection();
        int result = super.update(con, sql);
        JdbcUtil.releaseConnection(con);
        return result;
    }

    @Override
    public int update(String sql, Object param) throws SQLException {
        Connection con = JdbcUtil.getConnection();
        int result = super.update(con, sql, param);
        JdbcUtil.releaseConnection(con);
        return result;
    }

    @Override
    public int update(String sql, Object... params) throws SQLException {
        Connection con = JdbcUtil.getConnection();
        int result = super.update(con, sql, params);
        JdbcUtil.releaseConnection(con);
        return result;
    }
}

JdbcUtil.java

package util;

import com.mchange.v2.c3p0.ComboPooledDataSource;

import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.SQLException;

public class JdbcUtil {
    // 需要配置c3p0-config.xml
    private static ComboPooledDataSource dataSource = new ComboPooledDataSource();

    // 返回连接对象
    public static Connection getConnection() {
        try {
            return dataSource.getConnection();
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }

    // 返回连接池对象
    public static DataSource getDataSource() {
        return dataSource;
    }

    // 释放连接
    public static void releaseConnection(Connection connection) {

        try {
            connection.close();
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }

}

book.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

<h2>图书列表</h2>
分类：
<a href="book?method=findAll">全部</a>
<a href="book?method=findByCategory&category=1">第一类</a>
<a href="book?method=findByCategory&category=2">第二类</a>

<table border="1">
    <tr>
        <th>ID</th>
        <th>书名</th>
        <th>价格</th>
        <th>分类</th>
    </tr>
    <c:forEach items="${bookList}" var="book">
        <tr>
            <td>${book.bid}</td>
            <td>${book.bname}</td>
            <td>${book.price}</td>
            <td>${book.category}</td>
        </tr>
    </c:forEach>
</table>

配置文件

pom.xml

<dependency>
    <groupId>jstl</groupId>
    <artifactId>jstl</artifactId>
    <version>1.2</version>
</dependency>
<dependency>
    <groupId>taglibs</groupId>
    <artifactId>standard</artifactId>
    <version>1.1.2</version>
</dependency>

web.xml

<servlet-mapping>
    <servlet-name>BookServlet</servlet-name>
    <url-pattern>/book</url-pattern>
</servlet-mapping>

<servlet>
    <servlet-name>BookServlet</servlet-name>
    <servlet-class>com.pengshiyu.servlet.BookServlet</servlet-class>
</servlet>

c3p0-config.xml

<?xml version="1.0" encoding="utf-8"?>
<c3p0-config>
    <!-- 这是默认配置信息 -->
    <default-config>
        <!-- 连接四大参数配置 -->
        <property name="driverClass">com.mysql.cj.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql://localhost:3306/data</property>
        <property name="user">root</property>
        <property name="password">123456</property>

        <!-- 池参数配置 -->
        <property name="acquireIncrement">2</property>
        <property name="initialPoolSize">2</property>
        <property name="minPoolSize">2</property>
        <property name="maxPoolSize">10</property>
    </default-config>
</c3p0-config>

访问路径
http://localhost:8080/demo/book?method=findAll
http://localhost:8080/demo/book?method=findByCategory&category=1

课时10 案例4：页面静态化之如果文件存在直接重定向到html

使用一个过滤器，把servlet请求的资源输出保存到html中
第二次访问资源的时候，如果已存在就直接重定向到html文件

课时11 案例5：页面静态之生成html页面

CacheFilter.java

package com.pengshiyu.filter;

import com.pengshiyu.response.StaticResponse;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.IOException;

public class CacheFilter implements Filter {
    private FilterConfig config;
    private final String cacheFileName = "cache";
    private String cacheFilePath = null;

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        this.config = filterConfig;
        this.cacheFilePath = this.config.getServletContext().getRealPath(this.cacheFileName);

        File file = new File(this.cacheFilePath);
        if(file.exists()){
            file.mkdir();
        }
        
    }

    /**
     * 访问路径
     * http://localhost:8080/demo/book?method=findByCategory&category=4
     */
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse,
                         FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest)servletRequest;
        HttpServletResponse response = (HttpServletResponse)servletResponse;

        String category = request.getParameter("category");

        String filepath = this.cacheFilePath + "/" + category + ".html";
        File file = new File(filepath);

        // 如果页面不存在就缓存页面
        if(!file.exists()){
            StaticResponse staticResponse = new StaticResponse(response, filepath);
            filterChain.doFilter(request, staticResponse);
        }

        System.out.println("文件存在了");
        request.getRequestDispatcher(this.cacheFileName + "/" + category + ".html").forward(request, response);

    }

    @Override
    public void destroy() {

    }
}

StaticResponse.java

package com.pengshiyu.response;

import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.PrintWriter;

public class StaticResponse extends HttpServletResponseWrapper {
    private PrintWriter pw;

    public StaticResponse(HttpServletResponse response, String filename) throws FileNotFoundException {
        super(response);
        this.pw = new PrintWriter(filename);
    }

    @Override
    public PrintWriter getWriter() throws IOException {
        // 掉包输出流
        return this.pw;
    }
}

来源：CSDN

作者：彭世瑜

链接：https://blog.csdn.net/mouday/article/details/104456549