Servlet属性设置

Servlet中的属性是可以从以下范围之一设置，获取或删除的对象：

• 请求范围
• 会话范围
• 应用范围

Servlet程序员可以使用属性将信息从一个servlet传递给另一个servlet。它就像将对象从一个类传递给另一个类一样，以便我们可以一次又一次地重用同一个对象。

ServletRequest，HttpSession和ServletContext接口的属性特定方法

Servlet中有以下4种属性方法，它们具体如下：

ServletContext的示例设置和获取属性

在这个例子中，在应用程序范围内设置属性，并从另一个servlet获取该值。

打开Eclipse创建一个动态Web项目：ServletAttribute ，其完整的项目结构如下所示 -

以下是几个主要代码文件 -

文件： ServletAttr.java -

package com.zaixian;

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

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

/**
 * Servlet implementation class ServletAttr
 */

public class ServletAttr extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // TODO Auto-generated method stub
        try {
            response.setCharacterEncoding("UTF-8");
            response.setContentType("text/html");
            PrintWriter out = response.getWriter();

            ServletContext context = getServletContext();
            context.setAttribute("company", "Lenovo");
            out.println("Welcome to first servlet");
            out.println("在第二个Servlet<a href='servlet2'>查看属性值</a>");
            out.close();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

文件： ServletAttr2.java -

package com.zaixian;

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

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

/**
 * Servlet implementation class ServletAttr
 */

public class ServletAttr2 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html");
        PrintWriter out = response.getWriter();

        ServletContext context = getServletContext();
        String n = (String) context.getAttribute("company");

        out.println("Welcome to " + n);
        out.close();
    }

}

文件： 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"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
    id="WebApp_ID" version="3.0">
    <display-name>ServletAttribute</display-name>
    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
    </welcome-file-list>
    <servlet>
        <servlet-name>ServletAttr1</servlet-name>
        <servlet-class>com.zaixian.ServletAttr</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>ServletAttr1</servlet-name>
        <url-pattern>/servlet</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>ServletAttr2</servlet-name>
        <servlet-class>com.zaixian.ServletAttr2</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>ServletAttr2</servlet-name>
        <url-pattern>/servlet2</url-pattern>
    </servlet-mapping>
</web-app>

在编写完成上面的代码后，部署此Web应用程序，打开浏览器访问URL：http://localhost:8080/ServletAttribute/servlet ，如果程序没有错误，应该会看到以下结果 -

点击查看属性值链接，应该会看到以下结果 -

ServletConfig和ServletContext的区别

servletconfig对象引用单个servlet，而servletcontext对象引用整个Web应用程序。