一遍部落格帶你上手Servlet

鶴城發表於2023-03-29
Servlet

概念

Servlet其實就是Java提供的一門動態web資源開發技術。本質就是一個介面。

快速入門

  1. 建立web專案，匯入servlet依賴座標（注意依賴範圍scope，是provided，只在編譯和測試時使用）
    pom檔案：
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>tomcat-demo2</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.tomcat.maven</groupId>
                <artifactId>tomcat7-maven-plugin</artifactId>
                <version>2.2</version>
<!--                <configuration>-->
<!--                    <port>80</port>&lt;!&ndash; 訪問埠號 &ndash;&gt;-->
<!--                    <path>/</path>&lt;!&ndash; 專案訪問路徑 &ndash;&gt;-->
<!--                </configuration>-->
            </plugin></plugins>
    </build>

    <packaging>war</packaging>
    

</project>

  1. 建立：定義一個類，實現servlet介面，重寫介面中的方法
    在Java目錄下建立類，類名後加入implements Servlet實現介面，再CTRL+o重寫父類方法。

  2. 配置：在類上使用@WebServlet註解，配置該servlet的訪問路徑
    再在類名寫寫明路徑的註解。2、3步程式碼如下：

package com.itheijma.web;

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


@WebServlet("/demo1")
public class ServletDemo1 implements Servlet {

    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
        System.out.println("servlet hello world");

    }

    public String getServletInfo() {
        return null;
    }

    public void destroy() {

    }

    public void init(ServletConfig servletConfig) throws ServletException {

    }

    public ServletConfig getServletConfig() {
        return null;
    }
}
  1. 訪問，啟動tomcat，在瀏覽器中訪問
    隨後在網頁中訪問demo1，控制檯出現要輸出的資訊，說明servlet編寫成功。

Servlet執行流程

瀏覽器根據路徑向伺服器發出請求，伺服器再根據我們自定義的Servlet介面建立Servlet物件，再呼叫service方法，執行我們的程式碼。

Servlet生命週期

物件的生命週期指一個物件從被建立到銷燬的整個過程。
servlet執行在servlet容器中，其生命週期由容器來管理，分為四個階段：

  1. 載入和例項化：預設情況下，當servlet第一次被訪問時，由容器建立servlet物件。
  2. 初始化：在servlet例項化之後，容器呼叫servlet的init（）方法初始化這個物件。完成一些如載入配置檔案、建立連線等初始化的工作。注：該方法只被呼叫一次，因為一個servlet物件只被建立一次。
  3. 請求處理：每次請求servlet時，servlet容器都會呼叫servlet的service（）方法對請求進行處理。
  4. 服務終止：當需要釋放記憶體或容器關閉時，容器就會呼叫servlet例項的destory（）方法完成資源的釋放。
package com.itheijma.web;

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


@WebServlet(urlPatterns = "/demo2",loadOnStartup = 1)
public class ServletDemo2 implements Servlet {


    /**
     * 初始化方法
     * 1. 呼叫時機：預設情況下，servlet被第一次訪問時呼叫
     *  * loadOnStartup
     * 2. 呼叫次數：1次
     * @param servletConfig
     * @throws ServletException
     */
    public void init(ServletConfig servletConfig) throws ServletException {
        System.out.println("init....");

    }


    /**
     * 提供服務方法
     * 1. 呼叫時機：每一次servlet被訪問時呼叫
     * 2. 呼叫次數：多次
     *
     * @param servletRequest
     * @param servletResponse
     * @throws ServletException
     * @throws IOException
     */
    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {
        System.out.println("servlet hello world");

    }


    /**
     * 銷燬方法
     * 1. 呼叫時機：記憶體釋放或伺服器關閉的時候，servlet物件會被銷燬，呼叫
     * 2. 呼叫次數：一次
     */
    public void destroy() {
        System.out.println("destory.....");

    }


    public String getServletInfo() {
        return null;
    }


    public ServletConfig getServletConfig() {
        return null;
    }
}

Servlet體系結構

Servlet——Servlet體系根介面
GenericServlet——Servlet抽象實現類
HttpServlet——對HTTP協議封裝的Servlet實現類
因為我們開發的是B/S架構的web專案，都是針對HTTP協議的，所以我們自定義的Servlet，會繼承HttpServlet

package com.itheijma.web;

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 java.io.IOException;

@WebServlet("/demo3")
public class ServletDemo3 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("get...");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("post...");
    }
}

urlPattern配置

Servlet想要被訪問，必須配置其訪問路徑（urlPattern）

package com.itheijma.web;


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 java.io.IOException;

/**
 * urlPattern: 一個Servlet可以配置多個訪問路徑
 */
@WebServlet(urlPatterns = {"/demo4","/demo5"})
public class ServletDemo4 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("demo4 get.....");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    }
}


package com.itheijma.web;


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 java.io.IOException;

/**
 * urlPattern
 *  *目錄匹配 /user/*
 */
@WebServlet(urlPatterns = "/user/*")
public class ServletDemo6 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("demo6 get.....");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    }
}


package com.itheijma.web;


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 java.io.IOException;

/**
 * urlPattern
 *  *副檔名匹配： *.do
 */
@WebServlet(urlPatterns = "*.do")
public class ServletDemo7 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("demo7 get.....");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    }
}


package com.itheijma.web;


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 java.io.IOException;

/**
 * urlPattern
 *  *任意匹配 /*  /
 */
@WebServlet(urlPatterns = "/")
public class ServletDemo8 extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("demo8 get.....");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    }
}

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