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Spring Boot之 Servlet、Fiter、Listener的使用

Simon_Zhou / 857人閱讀

摘要：生長速度越快的樹木，其致密度就越低，生命往往也越短暫而松樹柏樹胡楊等樹種，要上百年才能成材，用起來卻可千年不朽。

Spring Boot之 Servlet、Fiter、Listener的使用

新建項目：http://start.spring.io/

Servlet的使用

新建MyServlet類

package com.adagio.chat.servlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.io.Writer;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet(
        name = "myservlet",
        urlPatterns = {"/myservlet1", "/myservlet2"}
)
public class MyServlet extends HttpServlet {

    @Override
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException{
        
        Writer writer = response.getWriter();
        writer.write("Hello World");
    }
}

啟動類添加注解 @ServletComponentScan(basePackages = {"com.adagio.chat.servlet"})

啟動運行訪問：http://localhost:8080/myservlet1和http://localhost:8080/myservlet2

servlet的使用很簡單：

添加注解 @WebServlet

配置name，可以不用配置

配置路徑，urlPatterns 可以配置多值

Filter的使用

使用方式和Servlet十分類似

package com.adagio.chat.servlet;

import java.io.IOException;

import javax.servlet.FilterChain;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.filter.OncePerRequestFilter;

//@WebFilter(servletNames = "myservlet")
@WebFilter(urlPatterns = "/myservlet1")
public class MyFilter extends OncePerRequestFilter {

    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
            throws ServletException, IOException {
        ServletContext servletContext = getServletContext();
        servletContext.log("url myservlet was filter");
        
        filterChain.doFilter(request, response);
    }

}

可以直接使用servletNames過濾，如@WebFilter(servletNames = "myservlet")，訪問http://localhost:8080/myservlet1和http://localhost:8080/myservlet2都會在控制臺打印日志

也可以使用@WebFilter(urlPatterns = "/myservlet1")，訪問上面兩個鏈接，只有訪問http://localhost:8080/myservlet1這個地址才會打印日志

Listener的使用

使用方式也是類似的

package com.adagio.chat.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpServletRequest;

@WebListener
public class MyListener implements ServletRequestListener {

    @Override
    public void requestDestroyed(ServletRequestEvent sre) {
        HttpServletRequest request = (HttpServletRequest)sre.getServletRequest();
        
        ServletContext servletContext = request.getServletContext();
        servletContext.log("request was destroyed");
    }

    @Override
    public void requestInitialized(ServletRequestEvent sre) {
        HttpServletRequest request = (HttpServletRequest)sre.getServletRequest();
        
        ServletContext servletContext = request.getServletContext();
        servletContext.log("request was initialized");
    }

}

訪問http://localhost:8080/myservlet2 觀察控制臺

執行順序 
2017-09-10 16:11:18.247  INFO 7692 --- [io-8080-exec-10] o.a.c.c.C.[Tomcat].[localhost].[/]       : request was initialized
2017-09-10 16:11:18.271  INFO 7692 --- [io-8080-exec-10] o.a.c.c.C.[Tomcat].[localhost].[/]       : url myservlet was filter
2017-09-10 16:11:18.271  INFO 7692 --- [io-8080-exec-10] o.a.c.c.C.[Tomcat].[localhost].[/]       : servlet was doGet
2017-09-10 16:11:18.275  INFO 7692 --- [io-8080-exec-10] o.a.c.c.C.[Tomcat].[localhost].[/]       : request was destroyed

先監聽器的初始化，再經過濾器，然后執行doGet方法，最后執行監聽器的消亡

使用注入的方式注冊

效果和上面的方式一樣的，具體實現見代碼

package com.adagio.chat.spring.boot;

import java.io.IOException;

import javax.servlet.FilterChain;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.context.request.RequestAttributes;
import org.springframework.web.context.request.RequestContextHolder;
import org.springframework.web.context.request.ServletRequestAttributes;
import org.springframework.web.filter.OncePerRequestFilter;

public class MyFilter2 extends OncePerRequestFilter {

    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
            throws ServletException, IOException {
//        ServletContext servletContext = getServletContext();
//        
//        //動態獲取URI
//        String requestURI = request.getRequestURI();
//        
//        servletContext.log("url "+requestURI+" was filter from MyFilter2");
        
        doSomething();
        filterChain.doFilter(request, response);
    }
    
    /**
     * 當沒有request的時候，可以使用這種方式獲取request
     */
    public void doSomething(){
        
        RequestAttributes requestAttributes = RequestContextHolder.getRequestAttributes();
        ServletRequestAttributes servletRequestAttributes = (ServletRequestAttributes)requestAttributes;
        
        HttpServletRequest request = servletRequestAttributes.getRequest();
        ServletContext servletContext = getServletContext();
        
        //動態獲取URI
        String requestURI = request.getRequestURI();
        
        servletContext.log("url "+requestURI+" was filter from MyFilter2");
        
    }

}

package com.adagio.chat.spring.boot;

import java.io.IOException;
import java.io.PrintWriter;
import java.io.Writer;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


public class MyServlet2 extends HttpServlet {

    @Override
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException{
        
        ServletContext servletContext = request.getServletContext();
        servletContext.log("servlet2 was doGet");
        
        Writer writer = response.getWriter();
        writer.write("Hello World From MyServlet2");
    }
}

package com.adagio.chat;

import javax.servlet.DispatcherType;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.boot.web.servlet.ServletComponentScan;
import org.springframework.boot.web.servlet.ServletListenerRegistrationBean;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;

import com.adagio.chat.servlet.MyListener;
import com.adagio.chat.spring.boot.MyFilter2;
import com.adagio.chat.spring.boot.MyServlet2;

@SpringBootApplication
@ServletComponentScan(basePackages = {"com.adagio.chat.servlet"})
public class ChatApplication {

    public static void main(String[] args) {
        SpringApplication.run(ChatApplication.class, args);
    }
    
    @Bean
    public static ServletRegistrationBean servletRegistrationBean(){
        ServletRegistrationBean servletRegistrationBean = new ServletRegistrationBean();
        
        servletRegistrationBean.setServlet(new MyServlet2());
        servletRegistrationBean.addUrlMappings("/spring/boot/myservelt2");
        servletRegistrationBean.setName("myservlet2");
        
        return servletRegistrationBean;
    }
    
    @Bean
    public static FilterRegistrationBean filterRegistrationBean(){
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
        
        filterRegistrationBean.setFilter(new MyFilter2());
//        filterRegistrationBean.addUrlPatterns("/spring/boot/myservelt2");
        filterRegistrationBean.addServletNames("myservlet2");
        filterRegistrationBean.setDispatcherTypes(DispatcherType.REQUEST, DispatcherType.FORWARD, DispatcherType.INCLUDE);
        
        return filterRegistrationBean;
    }
    
    /**
     * 監聽器會監聽所有請求
     * 可以重復注冊監聽器
     * @return
     */
    @Bean
    public static ServletListenerRegistrationBean servletListenerRegistrationBean(){
        ServletListenerRegistrationBean servletListenerRegistrationBean = new ServletListenerRegistrationBean<>(new MyListener());
        return servletListenerRegistrationBean;
    }
    
}

急事慢做：成長是長時間努力、積累和進步的結果，是水到渠成的事情，絕不是心急就能做到的。
生長速度越快的樹木，其致密度就越低，生命往往也越短暫；而松樹、柏樹、胡楊等樹種，要上百年才能成材，用起來卻可千年不朽。 - 俞敏洪

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