Web专题一：Servlet

Web专题一：Servlet

Servlet是用Java编写的服务器端程序，运行于支持Java的Web应用服务器中，可以响应HTTP请求

1.1. Servlet生命周期

1.1.1. init()方法

void init() throws ServletException

在Servlet第一次被创建时才会被调用，且只调用一次

1.1.2. service()方法

void service(ServletRequest req, ServletResponse res)
                 throws ServletException, IOException

Servlet容器在这里处理请求，根据请求的方法调用相应的doGet等方法，且每个请求都会产生一个新的线程

1.1.3. doGet()方法

void doGet(HttpServletRequest req, HttpServletResponse resp) 
                    throws ServletException, IOException

处理请求方法为GET的请求，更多request方法如下：

private static final String METHOD_DELETE = "DELETE";
private static final String METHOD_HEAD = "HEAD";
private static final String METHOD_GET = "GET";
private static final String METHOD_OPTIONS = "OPTIONS";
private static final String METHOD_POST = "POST";
private static final String METHOD_PUT = "PUT";
private static final String METHOD_TRACE = "TRACE";

1.1.4. doDestory()方法

销毁Servlet，只被调用一次

1.2. Servlet完整示例

1.2.1. 创建Servlet类

定义Servlet方法有3种：

• 实现Servlet接口
• 继承GenericServlet类
• 继承HttpServlet类

package org.ibu;

import javax.servlet.http.*;
import javax.servlet.*;
import java.io.IOException;
import java.util.logging.Logger;


public class SearchServlet extends HttpServlet {
    final Logger logger = Logger.getLogger(SearchServlet.class.getName());

    @Override
    public void init() throws ServletException
    {
        logger.info("Servlet::init()");
    }

    @Override
    public void service(ServletRequest req, ServletResponse res)
            throws ServletException, IOException {
        logger.info("Servlet::service()");
        super.service(req, res);
    }

    @Override
    public void doGet(HttpServletRequest request,
                      HttpServletResponse response)
            throws ServletException, IOException
    {
        logger.info("Servlet::doGet()");
    }

    @Override
    public void destroy()
    {
        logger.info("Servlet::destroy()");
    }
}

1.2.2. 配置Servlet

在/WEB-INF/web.xml添加Servlet配置，将URL映射到Servlet类，将/SearchServlet和/search映射到SearchServlet类上

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
        http://java.sun.com/xml/ns/javaee/web-app_4_0.xsd"
           version="4.0">
    <servlet>
        <servlet-name>SearchServlet</servlet-name>
        <servlet-class>org.ibu.SearchServlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>SearchServlet</servlet-name>
        <url-pattern>/SearchServlet</url-pattern>
        <url-pattern>/search</url-pattern>
    </servlet-mapping>
</web-app>

1.3. Servlet完整示例(注解方式)

1.3.1. 创建Servlet类

package org.ibu;

import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import javax.servlet.*;
import java.io.IOException;
import java.util.logging.Logger;

@WebServlet(name = "SearchServlet", 
        urlPatterns = {"/SearchServlet", "/search"})
public class SearchServlet extends HttpServlet {
    final Logger logger = Logger.getLogger(SearchServlet.class.getName());

    @Override
    public void init() throws ServletException
    {
        logger.info("Servlet::init()");
    }

    @Override
    public void service(ServletRequest req, ServletResponse res)
            throws ServletException, IOException {
        logger.info("Servlet::service()");
        super.service(req, res);
    }

    @Override
    public void doGet(HttpServletRequest request,
                      HttpServletResponse response)
            throws ServletException, IOException
    {
        logger.info("Servlet::doGet()");
    }

    @Override
    public void destroy()
    {
        logger.info("Servlet::destroy()");
    }
}

1.3.2. 配置Servlet

/WEB-INF/web.xml无需配置Servlet

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
        http://java.sun.com/xml/ns/javaee/web-app_4_0.xsd"
           version="4.0">
</web-app>

1.3.3. 生命周期示例

1. startup启动web服务器
2. 浏览器访问http://localhost:8080/SearchServlet
3. 浏览器访问http://localhost:8080/search
4. shutdown停止Web服务器

日志信息输出如下：

19-Apr-2020 11:19:49.521 信息 [http-nio-8080-exec-3] org.ibu.SearchServlet.init Servlet::init()
19-Apr-2020 11:19:49.522 信息 [http-nio-8080-exec-3] org.ibu.SearchServlet.service Servlet::service()
19-Apr-2020 11:19:49.523 信息 [http-nio-8080-exec-3] org.ibu.SearchServlet.doGet Servlet::doGet()
19-Apr-2020 11:20:14.163 信息 [http-nio-8080-exec-8] org.ibu.SearchServlet.service Servlet::service()
19-Apr-2020 11:20:14.163 信息 [http-nio-8080-exec-8] org.ibu.SearchServlet.doGet Servlet::doGet()
...
19-Apr-2020 11:20:20.506 信息 [localhost-startStop-2] org.ibu.SearchServlet.destroy Servlet::destroy()

Web专题一：Servlet

原文：https://www.cnblogs.com/myibu/p/12776181.html