Servlet取得初始化配置信息及內置對象 – JAVA編程語言程序開發技術文章

Servlet取得初始化配置信息：

通過config對象可以讀取web.xml中的配置的初始化參數，此對象實際上是ServletConfig借口的實例。可以通過init()方法找到ServletConfig接口實例。

讀取初始化配置信息——InitParamServlet.java

[java]
package com.ls.servlet_01;

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

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class InitParamServlet extends HttpServlet {

    String initParam=null;
    public void init(ServletConfig config) throws ServletException {
        this.initParam=config.getInitParameter("ref");
    }
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        System.out.println("初始化參數："+this.initParam);

    }
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        this.doGet(request, response);
    }
}
在web.xml中配置初始化信息

[java]
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
    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_2_5.xsd">
<servlet>
    <servlet-name>InitParamServlet</servlet-name>
    <servlet-class>com.ls.servletd_01.InitParamServlet</servlet-class>
    <init-param>
        <param-name>ref</param-name>
        <param-value>liusheng</param-value>
    </init-param>
</servlet>
<servlet-mapping>
    <servlet-name>InitParamServlet</servlet-name>
    <url-pattern>/InitParamServlet</url-pattern>
</servlet-mapping>
<welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>

程序運行結果：在Tomcat後臺打印

初始化參數：liusheng

用<init-param>直接配置初始化

<param-name>表示參數名稱

<param-value>表示參數的內容

註意：

在Servlet中初始化方法一共有init（）和init（ServletConfig config）兩個，如果兩個初始化方法同時出現，則調用的是init（ServletConfig config）方法。

Servlet取得其他內置對象：

1、取得HttpSession實例

在servlet程序中要想取得一個session對象，則可以通過HttpServletRequest接口完成，有以下操作方法：

public HttpSession getSession() 返回當前的session

public HttpSession getSession（boolean create）返回當前的session，如果沒有則創建一個新的session對象返回

取得HttpSession對象—HttpSessionservlet.java

[java]
package com.ls.servlet_02;

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

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class HttpSessionservlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        HttpSession ses = request.getSession();
        System.out.println("SESSION–>" + ses.getId());
        ses.setAttribute("username", "劉勝");
        System.out.println("username屬性內容是：" + ses.getAttribute("username"));
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        this.doGet(request, response);

    }

}
配置web.xml文件

[java]
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
    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_2_5.xsd">
<servlet>
    <servlet-name>HttpSession</servlet-name>
    <servlet-class>com.ls.servlet_02.HttpSessionservlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>HttpSession</servlet-name>
    <url-pattern>/servlet_HttpSession</url-pattern>
</servlet-mapping>
<welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>

程序運行結果： Tomcat後臺顯示

本程序通過getSession()方法取得瞭一個HttpSession對象後，輸出瞭Session Id以及屬性的設置及取得操作。

2、取得ServletContext實例

application內置對象是ServletContext 接口的實例，表示的是Servlet上下文。如果要在一個servlet中使用此現象，直接通過GenericServlet類提供的方法即可：

public ServletContext getServletContext（）取得ServletContext對象

取得application對象—–ServletContext.java

[java]
package com.ls.servlet_03;

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

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

public class ServletContext extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        javax.servlet.ServletContext app =super.getServletContext();
        System.out.println("真實路徑："+app.getRealPath("/"));
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        this.doGet(request, response);
    }


}

配置web.xml文件

[java]
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
    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_2_5.xsd">
<servlet>
    <servlet-name>ServletContext</servlet-name>
    <servlet-class>com.ls.servlet_03.ServletContext</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>ServletContext</servlet-name>
    <url-pattern>/servlet_ServletContext</url-pattern>
</servlet-mapping>
<welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>

程序運行結果： Tomcat後臺輸出

本程序通過getServletContext()方法取得ServletContext實例後，將虛擬目錄所對應的真實路徑輸出。

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