JavaWeb学习总结（四）—ServletConfig和ServletContext

一、ServletConfig

1. ServletConfig介绍：#

ServletConfig是Servlet中的init()方法的参数类型，服务器会在调用init()方法时传递ServletConfig对象给init()方法。
  ServletConfig对象封装了Servlet在web.xml中的配置信息，它对应<servlet>元素。ServletConfig类的功能有：

1.  String getServletName()：获取Servlet配置名，即<servlet-name>的值；
2.  ServletContext getServletContext()：获取ServletContext对象，这个对象稍后介绍
3.  String getInitParameter(String name)：获取初始化参数
4.  Enumeration getInitParameterNames()：获取所有初始化参数的名称

  2. 在web.xml文件中，配置<servlet>时可以为<servlet>配置0~N个初始化参数，例如#

<servlet>
    <servlet-name>ServletContextDemo1</servlet-name>
    <servlet-class>com.web.study.ServletContextDemo1</servlet-class>
    <!-- 配置ServletConfigDemo1的初始化参数 -->
    <init-param>
        <param-name>name</param-name>
        <param-value>scott</param-value>
    </init-param>
    <init-param>
        <param-name>password</param-name>
        <param-value>tiger</param-value>
    </init-param>
    <init-param>
        <param-name>charset</param-name>
        <param-value>utf-8</param-value>
    </init-param>
  </servlet>

3. 通过ServletConfig获取当前Servlet的初始化参数#

package com.web.study;
import java.io.IOException;
import java.util.Enumeration;

import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.sun.jmx.snmp.Enumerated;

public class ServletContextDemo1 extends HttpServlet {

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

       ServletConfig config = this.getServletConfig();
     //获取指定的初始化参数
       String p1 = config.getInitParameter("name");  
       response.getWriter().print(p1);
       response.getWriter().print("<hr/>");

      //获取所有的初始化参数
       Enumeration<String> e = config.getInitParameterNames();
       while (e.hasMoreElements()){
           String names = e.nextElement();
           String value = config.getInitParameter(names);
           response.getWriter().print(names + "=" + value + "<br/>");
       }
    }

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

运行输出：

 

二、ServletContext#

1.ServletContext简介：#

     ServletContext是Servlet三大域对象之一，ServletContext在服务器启动时创建，在服务器关闭时销毁，一个JavaWeb应用只创建一个ServletContext对象，在HttpServlet中可以通过以下方法来获取ServletContext对象：
  1.  ServletContext sc = this.getServletContext()
  2. ServletContext sc = this.getServletConfig().getServletContext()

2.ServletContext的应用#

1.读取web.xml中配置的应用初始化参数,注意这个读取的不是某一个Servlet的初始化参会数，而是全局的。#

 <!-- 全局的初始化参数 -->
  <context-param>
      <param-name>p1</param-name>
      <param-value>v1</param-value>      
  </context-param>
  <context-param> 
      <param-name>p2</param-name>
      <param-value>v2</param-value>      
  </context-param>

代码如下：

package com.web.study;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

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

public class ServletContextDemo5 extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html");
        //获取ServletContext
        ServletContext context = this.getServletContext();
        //得到参数
        String value1 = context.getInitParameter("p1");
        response.getWriter().print(value1);    
    }

}

浏览器将会输出：v1.

 

2.多个Servlet实现数据共享。#

ServletContextDemo3往ServletContext中储存数据。

package com.web.study;

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;

public class ServletContextDemo3 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html");
        ServletContext context = this.getServletContext();
        //将data存储到ServletContext对象中
        context.setAttribute("scott", "tiger");
            
    }
}

ServletContextDemo3往ServletContext中读取数据。

package com.web.study;

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;

public class ServletContextDemo4 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html");
        ServletContext context = this.getServletContext();
        /*
         * 从ServletContext对象中取出数据
         */
        String name = (String) context.getAttribute("scott");
        response.getWriter().print(name);
    }

}

先访问ServletContextDemo3，再访问ServletContextDemo4，访问输出：

 #

3.用servletContext实现请求转发#

利用ServletContextDemo6转发请求

package com.web.study;

import java.io.IOException;

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

public class ServletContextDemo6 extends HttpServlet {

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

        response.setContentType("text/html");
        String data = "<h1><font color='red'>我是ServletContextDemo6</font></h1>";
        response.getOutputStream().write(data.getBytes());
        //获取ServletContext对象
        ServletContext context = this.getServletContext();
        //获取请求转发对象
        RequestDispatcher rd = context.getRequestDispatcher("/ServletContextDemo7");
        //调用forward方法实现请求转发
        rd.forward(request, response);
    }

}

ServletContextDemo7

package com.web.study;

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 ServletContextDemo7 extends HttpServlet {

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

        response.setContentType("text/html");
        response.getOutputStream().write("我是servletDemo7".getBytes());
        
    }

}

结果如下：

ServletContextDemo6页面应该是：

 

4.利用ServletContext对象读取资源文件#

资源文件分部如下：

properties的内容：

type=oracle
driver=oracle.jdbc.driver.OracleDriver
url=jdbc:oracle:thin:@192.168.0.90:1521:wluat
username=jeedev
password=jeedev

实现代码：

package com.web.study;


import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.text.MessageFormat;
import java.util.Properties;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * 使用servletContext读取资源文件
 */
public class ServletContextDemo8 extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException { 
        /**
         * response.setContentType("text/html;charset=UTF-8");目的是控制浏览器用UTF-8进行解码；
         * 这样就不会出现中文乱码了
         */
        response.setHeader("content-type","text/html;charset=UTF-8");
        readSrcDirPropCfgFile(response);//读取src目录下的properties配置文件
        response.getWriter().println("<hr/>");
        readWebRootDirPropCfgFile(response);//读取WebRoot目录下的properties配置文件
        response.getWriter().println("<hr/>");
        readPropCfgFile(response);//读取src目录下的db.config包中的db3.properties配置文件
        response.getWriter().println("<hr/>");
        readPropCfgFile2(response);//读取src目录下的com.web.study包中的db4.properties配置文件
        
    }

    /**
     * 读取src目录下的com.web.study包中的db4.properties配置文件
     * @param response
     * @throws IOException
     */
    private void readPropCfgFile2(HttpServletResponse response)
            throws IOException {
        InputStream in = this.getServletContext().getResourceAsStream("/WEB-INF/classes/com/web/study/db4.properties");
        Properties prop = new Properties();
        prop.load(in);
        String driver = prop.getProperty("driver");
        String url = prop.getProperty("url");
        String username = prop.getProperty("username");
        String password = prop.getProperty("password");
        response.getWriter().println("读取src目录下的com.web.study包中的db4.properties配置文件：");
        response.getWriter().println(
                MessageFormat.format(
                        "driver={0},url={1},username={2},password={3}", 
                        driver,url, username, password));
    }

    /**
     * 读取src目录下的db.config包中的db3.properties配置文件
     * @param response
     * @throws FileNotFoundException
     * @throws IOException
     */
    private void readPropCfgFile(HttpServletResponse response)
            throws FileNotFoundException, IOException {
        //通过ServletContext获取web资源的绝对路径“D:\Program\apache-tomcat-6.0.45\webapps\ServletDemo\WEB-INF\classes\db\config\db3.properties”
        String path = this.getServletContext().getRealPath("/WEB-INF/classes/db/config/db3.properties");
        InputStream in = new FileInputStream(path);
        Properties prop = new Properties();
        prop.load(in);
        String driver = prop.getProperty("driver");
        String url = prop.getProperty("url");
        String username = prop.getProperty("username");
        String password = prop.getProperty("password");
        response.getWriter().println("读取src目录下的db.config包中的db3.properties配置文件：");
        response.getWriter().println(
                MessageFormat.format(
                        "driver={0},url={1},username={2},password={3}", 
                        driver,url, username, password));
    }

    /**
     * 通过ServletContext对象读取WebRoot目录下的properties配置文件
     * @param response
     * @throws IOException
     */
    private void readWebRootDirPropCfgFile(HttpServletResponse response)
            throws IOException {
        /**
         * 通过ServletContext对象读取WebRoot目录下的properties配置文件
         * “/”代表的是项目根目录
         */
        InputStream in = this.getServletContext().getResourceAsStream("/db2.properties");
        Properties prop = new Properties();
        prop.load(in);
        String driver = prop.getProperty("driver");
        String url = prop.getProperty("url");
        String username = prop.getProperty("username");
        String password = prop.getProperty("password");
        response.getWriter().println("读取WebRoot目录下的db2.properties配置文件：");
        response.getWriter().print(
                MessageFormat.format(
                        "driver={0},url={1},username={2},password={3}", 
                        driver,url, username, password));
    }

    /**
     * 通过ServletContext对象读取src目录下的properties配置文件
     * @param response
     * @throws IOException
     */
    private void readSrcDirPropCfgFile(HttpServletResponse response) throws IOException {
        /**
         * 通过ServletContext对象读取src目录下的db1.properties配置文件
         */
        InputStream in = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db1.properties");
        Properties prop = new Properties();
        prop.load(in);
        String driver = prop.getProperty("driver");
        String url = prop.getProperty("url");
        String username = prop.getProperty("username");
        String password = prop.getProperty("password");
        response.getWriter().println("读取src目录下的db1.properties配置文件：");
        response.getWriter().println(
                MessageFormat.format(
                        "driver={0},url={1},username={2},password={3}", 
                        driver,url, username, password));
    }

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

}

运行结果如下：

 

使用类装载器读取资源文件#

package com.web.study;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.text.MessageFormat;
import java.util.Properties;

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

public class ServletcontextDemo9 extends HttpServlet {

    

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        /**
         * response.setContentType("text/html;charset=UTF-8");目的是控制浏览器用UTF-8进行解码；
         * 这样就不会出现中文乱码了
         */
        response.setHeader("content-type","text/html;charset=UTF-8");
        test1(response);
        response.getWriter().println("<hr/>");
        test2(response);
        response.getWriter().println("<hr/>");
        
        
    }
    
    /**
     * 读取类路径下的资源文件
     * @param response
     * @throws IOException
     */
    private void test1(HttpServletResponse response) throws IOException {
        //获取到装载当前类的类装载器
        ClassLoader loader = ServletContextDemo7.class.getClassLoader();
        //用类装载器读取src目录下的db1.properties配置文件
        InputStream in = loader.getResourceAsStream("db1.properties");
        Properties prop = new Properties();
        prop.load(in);
        String driver = prop.getProperty("driver");
        String url = prop.getProperty("url");
        String username = prop.getProperty("username");
        String password = prop.getProperty("password");
        response.getWriter().println("用类装载器读取src目录下的db1.properties配置文件：");
        response.getWriter().println(
                MessageFormat.format(
                        "driver={0},url={1},username={2},password={3}", 
                        driver,url, username, password));
    }

    /**
     * 读取类路径下面、包下面的资源文件
     * @param response
     * @throws IOException
     */
    private void test2(HttpServletResponse response) throws IOException {
        //获取到装载当前类的类装载器
        ClassLoader loader = ServletContextDemo7.class.getClassLoader();
        //用类装载器读取src目录下的gacl.servlet.study包中的db4.properties配置文件
        InputStream in = loader.getResourceAsStream("com/web/study/db4.properties");
        Properties prop = new Properties();
        prop.load(in);
        String driver = prop.getProperty("driver");
        String url = prop.getProperty("url");
        String username = prop.getProperty("username");
        String password = prop.getProperty("password");
        response.getWriter().println("用类装载器读取src目录下的gacl.servlet.study包中的db4.properties配置文件：");
        response.getWriter().println(
                MessageFormat.format(
                        "driver={0},url={1},username={2},password={3}", 
                        driver,url, username, password));
    }
    
    /**
     * 通过类装载器读取资源文件的注意事项:不适合装载大文件，否则会导致jvm内存溢出
     */
 
    
    
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        this.doGet(request, response);
    }

}

访问输出：