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javaweb Servlet開辟總結（二）

編輯：關於JAVA

javaweb Servlet開辟總結（二）。本站提示廣大學習愛好者：（javaweb Servlet開辟總結（二））文章只能為提供參考，不一定能成為您想要的結果。以下是javaweb Servlet開辟總結（二）正文

1、ServletConfig講授

1.1、設置裝備擺設Servlet初始化參數

　　在Servlet的設置裝備擺設文件web.xml中，可使用一個或多個<init-param>標簽為servlet設置裝備擺設一些初始化參數。

例如：

<servlet>
 <servlet-name>ServletConfigDemo1</servlet-name>
 <servlet-class>gacl.servlet.study.ServletConfigDemo1</servlet-class>
 <!--設置裝備擺設ServletConfigDemo1的初始化參數 -->
 <init-param>
  <param-name>name</param-name>
  <param-value>gacl</param-value>
 </init-param>
  <init-param>
  <param-name>password</param-name>
  <param-value>123</param-value>
 </init-param>
 <init-param>
  <param-name>charset</param-name>
  <param-value>UTF-8</param-value>
 </init-param>
</servlet>

1.2、經由過程ServletConfig獲得Servlet的初始化參數

　　當servlet設置裝備擺設了初始化參數後，web容器在創立servlet實例對象時，會主動將這些初始化參數封裝到ServletConfig對象中，並在挪用servlet的init辦法時，將ServletConfig對象傳遞給servlet。進而，我們經由過程ServletConfig對象便可以獲得以後servlet的初始化參數信息。

例如：

package gacl.servlet.study;

import java.io.IOException;
import java.util.Enumeration;
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 ServletConfigDemo1 extends HttpServlet {

 /**
  * 界說ServletConfig對象來吸收設置裝備擺設的初始化參數
  */
 private ServletConfig config;
 
 /**
  * 當servlet設置裝備擺設了初始化參數後，web容器在創立servlet實例對象時，
  * 會主動將這些初始化參數封裝到ServletConfig對象中，並在挪用servlet的init辦法時，
  * 將ServletConfig對象傳遞給servlet。進而，法式員經由過程ServletConfig對象便可以
  * 獲得以後servlet的初始化參數信息。
  */
 @Override
 public void init(ServletConfig config) throws ServletException {
  this.config = config;
 }

 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  //獲得在web.xml中設置裝備擺設的初始化參數
  String paramVal = this.config.getInitParameter("name");//獲得指定的初始化參數
  response.getWriter().print(paramVal);
  
  response.getWriter().print("<hr/>");
  //獲得一切的初始化參數
  Enumeration<String> e = config.getInitParameterNames();
  while(e.hasMoreElements()){
   String name = e.nextElement();
   String value = config.getInitParameter(name);
   response.getWriter().print(name + "=" + value + "<br/>");
  }
 }

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

}

運轉成果以下：

2、ServletContext對象

　　WEB容器在啟動時，它會為每一個WEB運用法式都創立一個對應的ServletContext對象，它代表以後web運用。
　　ServletConfig對象中保護了ServletContext對象的援用，開辟人員在編寫servlet時，可以經由過程ServletConfig.getServletContext辦法取得ServletContext對象。
　　因為一個WEB運用中的一切Servlet同享統一個ServletContext對象，是以Servlet對象之間可以經由過程ServletContext對象來完成通信。ServletContext對象平日也被稱之為context域對象。

3、ServletContext的運用

3.1、多個Servlet經由過程ServletContext對象完成數據同享

典范：ServletContextDemo1和ServletContextDemo2經由過程ServletContext對象完成數據同享

package gacl.servlet.study;

import java.io.IOException;
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 ServletContextDemo1 extends HttpServlet {

 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  String data = "xdp_gacl";
  /**
   * ServletConfig對象中保護了ServletContext對象的援用，開辟人員在編寫servlet時，
   * 可以經由過程ServletConfig.getServletContext辦法取得ServletContext對象。
   */
  ServletContext context = this.getServletConfig().getServletContext();//取得ServletContext對象
  context.setAttribute("data", data); //將data存儲到ServletContext對象中
 }

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

package gacl.servlet.study;

import java.io.IOException;
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 ServletContextDemo2 extends HttpServlet {

 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  ServletContext context = this.getServletContext();
  String data = (String) context.getAttribute("data");//從ServletContext對象中掏出數據
  response.getWriter().print("data="+data);
 }

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

　　先運轉ServletContextDemo1，將數據data存儲到ServletContext對象中，然後運轉ServletContextDemo2便可以從ServletContext對象中掏出數據了，如許就完成了數據同享，以下圖所示：

3.2、獲得WEB運用的初始化參數

在web.xml文件中應用<context-param>標簽設置裝備擺設WEB運用的初始化參數，以下所示：

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0" 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_3_0.xsd">
 <display-name></display-name>
 <!-- 設置裝備擺設WEB運用的初始化參數 -->
 <context-param>
  <param-name>url</param-name>
  <param-value>jdbc:mysql://localhost:3306/test</param-value>
 </context-param>

 <welcome-file-list>
  <welcome-file>index.jsp</welcome-file>
 </welcome-file-list>
</web-app>

獲得Web運用的初始化參數，代碼以下：

package gacl.servlet.study;

import java.io.IOException;
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 {

  ServletContext context = this.getServletContext();
  //獲得全部web站點的初始化參數
  String contextInitParam = context.getInitParameter("url");
  response.getWriter().print(contextInitParam);
 }

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

}

運轉成果：

3.3、用servletContext完成要求轉發

ServletContextDemo4

package gacl.servlet.study;

import java.io.IOException;
import java.io.PrintWriter;
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 ServletContextDemo4 extends HttpServlet {

 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  String data = "<h1><font color='red'>abcdefghjkl</font></h1>";
  response.getOutputStream().write(data.getBytes());
  ServletContext context = this.getServletContext();//獲得ServletContext對象
  RequestDispatcher rd = context.getRequestDispatcher("/servlet/ServletContextDemo5");//獲得要求轉發對象(RequestDispatcher)
  rd.forward(request, response);//挪用forward辦法完成要求轉發
 }

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

ServletContextDemo5

package gacl.servlet.study;

import java.io.IOException;
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.getOutputStream().write("servletDemo5".getBytes());
 }

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

}

運轉成果：

拜訪的是ServletContextDemo4，閱讀器顯示的倒是ServletContextDemo5的內容，這就是應用ServletContext完成了要求轉發

3.4、應用ServletContext對象讀取資本文件

項目目次構造以下：

代碼典范：應用servletContext讀取資本文件

package gacl.servlet.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;

/**
 * 應用servletContext讀取資本文件
 * 
 * @author gacl
 * 
 */
public class ServletContextDemo6 extends HttpServlet {

 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException { 
  /**
   * response.setContentType("text/html;charset=UTF-8");目標是掌握閱讀器用UTF-8停止解碼；
   * 如許就不會湧現中文亂碼了
   */
  response.setHeader("content-type","text/html;charset=UTF-8");
  readSrcDirPropCfgFile(response);//讀取src目次下的properties設置裝備擺設文件
  response.getWriter().println("<hr/>");
  readWebRootDirPropCfgFile(response);//讀取WebRoot目次下的properties設置裝備擺設文件
  response.getWriter().println("<hr/>");
  readPropCfgFile(response);//讀取src目次下的db.config包中的db3.properties設置裝備擺設文件
  response.getWriter().println("<hr/>");
  readPropCfgFile2(response);//讀取src目次下的gacl.servlet.study包中的db4.properties設置裝備擺設文件
  
 }

 /**
  * 讀取src目次下的gacl.servlet.study包中的db4.properties設置裝備擺設文件
  * @param response
  * @throws IOException
  */
 private void readPropCfgFile2(HttpServletResponse response)
   throws IOException {
  InputStream in = this.getServletContext().getResourceAsStream("/WEB-INF/classes/gacl/servlet/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("讀取src目次下的gacl.servlet.study包中的db4.properties設置裝備擺設文件：");
  response.getWriter().println(
    MessageFormat.format(
      "driver={0},url={1},username={2},password={3}", 
      driver,url, username, password));
 }

 /**
  * 讀取src目次下的db.config包中的db3.properties設置裝備擺設文件
  * @param response
  * @throws FileNotFoundException
  * @throws IOException
  */
 private void readPropCfgFile(HttpServletResponse response)
   throws FileNotFoundException, IOException {
  //經由過程ServletContext獲得web資本的相對途徑
  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("讀取src目次下的db.config包中的db3.properties設置裝備擺設文件：");
  response.getWriter().println(
    MessageFormat.format(
      "driver={0},url={1},username={2},password={3}", 
      driver,url, username, password));
 }

 /**
  * 經由過程ServletContext對象讀取WebRoot目次下的properties設置裝備擺設文件
  * @param response
  * @throws IOException
  */
 private void readWebRootDirPropCfgFile(HttpServletResponse response)
   throws IOException {
  /**
   * 經由過程ServletContext對象讀取WebRoot目次下的properties設置裝備擺設文件
   * “/”代表的是項目根目次
   */
  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("讀取WebRoot目次下的db2.properties設置裝備擺設文件：");
  response.getWriter().print(
    MessageFormat.format(
      "driver={0},url={1},username={2},password={3}", 
      driver,url, username, password));
 }

 /**
  * 經由過程ServletContext對象讀取src目次下的properties設置裝備擺設文件
  * @param response
  * @throws IOException
  */
 private void readSrcDirPropCfgFile(HttpServletResponse response) throws IOException {
  /**
   * 經由過程ServletContext對象讀取src目次下的db1.properties設置裝備擺設文件
   */
  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("讀取src目次下的db1.properties設置裝備擺設文件：");
  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);
 }

}

運轉成果以下：

代碼典范：應用類裝載器讀取資本文件

package gacl.servlet.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;

/**
 * 用類裝載器讀取資本文件
 * 經由過程類裝載器讀取資本文件的留意事項:不合適裝載年夜文件，不然會招致jvm內存溢出
 * @author gacl
 *
 */
public class ServletContextDemo7 extends HttpServlet {

 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  /**
   * response.setContentType("text/html;charset=UTF-8");目標是掌握閱讀器用UTF-8停止解碼；
   * 如許就不會湧現中文亂碼了
   */
  response.setHeader("content-type","text/html;charset=UTF-8");
  test1(response);
  response.getWriter().println("<hr/>");
  test2(response);
  response.getWriter().println("<hr/>");
  //test3();
  test4();
  
 }
 
 /**
  * 讀取類途徑下的資本文件
  * @param response
  * @throws IOException
  */
 private void test1(HttpServletResponse response) throws IOException {
  //獲得到裝載以後類的類裝載器
  ClassLoader loader = ServletContextDemo7.class.getClassLoader();
  //用類裝載器讀取src目次下的db1.properties設置裝備擺設文件
  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("用類裝載器讀取src目次下的db1.properties設置裝備擺設文件：");
  response.getWriter().println(
    MessageFormat.format(
      "driver={0},url={1},username={2},password={3}", 
      driver,url, username, password));
 }

 /**
  * 讀取類途徑上面、包上面的資本文件
  * @param response
  * @throws IOException
  */
 private void test2(HttpServletResponse response) throws IOException {
  //獲得到裝載以後類的類裝載器
  ClassLoader loader = ServletContextDemo7.class.getClassLoader();
  //用類裝載器讀取src目次下的gacl.servlet.study包中的db4.properties設置裝備擺設文件
  InputStream in = loader.getResourceAsStream("gacl/servlet/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("用類裝載器讀取src目次下的gacl.servlet.study包中的db4.properties設置裝備擺設文件：");
  response.getWriter().println(
    MessageFormat.format(
      "driver={0},url={1},username={2},password={3}", 
      driver,url, username, password));
 }
 
 /**
  * 經由過程類裝載器讀取資本文件的留意事項:不合適裝載年夜文件，不然會招致jvm內存溢出
  */
 public void test3() {
  /**
   * 01.avi是一個150多M的文件，應用類加載器去讀取這個年夜文件時會招致內存溢出：
   * java.lang.OutOfMemoryError: Java heap space
   */
  InputStream in = ServletContextDemo7.class.getClassLoader().getResourceAsStream("01.avi");
  System.out.println(in);
 }
 
 /**
  * 讀取01.avi,並拷貝到e:\根目次下
  * 01.avi文件太年夜，只能用servletContext去讀取
  * @throws IOException
  */
 public void test4() throws IOException {
  // path=G:\Java進修視頻\JavaWeb進修視頻\JavaWeb\day05視頻\01.avi
  // path=01.avi
  String path = this.getServletContext().getRealPath("/WEB-INF/classes/01.avi");
  /**
   * path.lastIndexOf("\\") + 1是一個異常絕妙的寫法
   */
  String filename = path.substring(path.lastIndexOf("\\") + 1);//獲得文件名
  InputStream in = this.getServletContext().getResourceAsStream("/WEB-INF/classes/01.avi");
  byte buffer[] = new byte[1024];
  int len = 0;
  OutputStream out = new FileOutputStream("e:\\" + filename);
  while ((len = in.read(buffer)) > 0) {
   out.write(buffer, 0, len);
  }
  out.close();
  in.close();
 }

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

  this.doGet(request, response);
 }

}

運轉成果以下：

4、在客戶端緩存Servlet的輸入

關於不常常變更的數據，在servlet中可認為其設置公道的緩存時光值，以免閱讀器頻仍向辦事器發送要求，晉升辦事器的機能。例如：

package gacl.servlet.study;

import java.io.IOException;

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

public class ServletDemo5 extends HttpServlet {

 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  String data = "abcddfwerwesfasfsadf";
  /**
   * 設置數據公道的緩存時光值，以免閱讀器頻仍向辦事器發送要求，晉升辦事器的機能
   * 這裡是將數據的緩存時光設置為1天
   */
  response.setDateHeader("expires",System.currentTimeMillis() + 24 * 3600 * 1000);
  response.getOutputStream().write(data.getBytes());
 }

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

  this.doGet(request, response);
 }

}

以上就是本文的全體內容，願望對年夜家控制javaweb Servlet開辟技巧有所贊助。