java Filter的简单使用

java web中的过滤器的简单使用、直接上代码。
1、web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
    version="3.0">
    <display-name>testFilter</display-name>
    
    <filter>
        <filter-name>filter1</filter-name>
        <filter-class>test_servlet_package.SimpleFilter1</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>filter1</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

    <filter>
        <filter-name>filter2</filter-name>
        <filter-class>test_servlet_package.SimpleFilter2</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>filter2</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

    <servlet>
        <servlet-name>testServlet</servlet-name>
        <servlet-class>test_servlet_package.test_servlet</servlet-class>
        <init-param> 
            <param-name>test</param-name> 
            <param-value>test1</param-value> 
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>testServlet</servlet-name>
        <url-pattern>/testServlet</url-pattern>
    </servlet-mapping>
</web-app>

2、test_servlet.java、SimpleFilter2.java、SimpleFilter1.java

package test_servlet_package;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
public class SimpleFilter1 implements Filter {
    // 随着容器 一起 起来 。。。初始化。。。
    @SuppressWarnings("unused")
    private FilterConfig filterConfig;
    public void init(FilterConfig config) throws ServletException {
        this.filterConfig = config;
    }
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) {
        try {
            System.out.println("Within SimpleFilter1:Filtering the Request...");
            chain.doFilter(request, response);// 把处理发送到下一个过滤器
            System.out.println("Within SimpleFilter1:Filtering the Response...");
        } catch (IOException ioe) {
            ioe.printStackTrace();
        } catch (ServletException se) {
            se.printStackTrace();
        }
    }
    public void destroy() {
        this.filterConfig = null;
    }
}

package test_servlet_package;

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class SimpleFilter2 implements Filter {
    @SuppressWarnings("unused")
    private FilterConfig filterConfig;

    public void init(FilterConfig config) throws ServletException {
        this.filterConfig = config;
    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) {
        try {
            System.out.println("Within SimpleFilter2:Filtering the Request...");
            chain.doFilter(request, response); // 把处理发送到下一个过滤器
            System.out.println("Within SimpleFilter2:Filtering the Response...");
        } catch (IOException ioe) {
            ioe.printStackTrace();
        } catch (ServletException se) {
            se.printStackTrace();
        }
    }

    public void destroy() {
        this.filterConfig = null;
    }
    /*
     * Within SimpleFilter1:Filtering the Request... Within
     * SimpleFilter2:Filtering the Request... Within SimpleFilter2:Filtering the
     * Response... Within SimpleFilter1:Filtering the Response...
     */
}

package test_servlet_package;
import java.io.IOException;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class test_servlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    // servlet 第一次 请求 被初始化 ,对象 在 容器 里 只有 一个
    // 但是 在 web.xml 配置 了 <load-on-startup>1</load-on-startup> 则 会 立刻 启动初始化
    // 初始化
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
        // 从配置文件中获得初始化参数
        String test = config.getInitParameter("test");
        ServletContext context = this.getServletContext();
        String filePath = context.getRealPath(test);
        System.out.println("filePath：" + filePath);
    }
    protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
        ServletConfig config = this.getServletConfig();
        ServletContext servletContext =  this.getServletContext();
        res.getWriter().println("test");
        res.getWriter().close();
    
    }
    protected void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
        doGet(req, res);
    }
}