ServletContext的使用:
每個web工程都只有一個ServletContext對象,所以在哪裏獲得的ServletContext對象都是同一個.
作用：
1.可以獲取全局配置參數
2.可以獲取web應用中的資源
1)獲取資源在tomcat裏面的絕對路徑,使用getRealPath()方法,先獲取路徑再獲取流對象.
2)使用getResourceAsStream(),根據相對路徑直接獲取流對象
3)通過classloader(類加載器JDBC)去獲取web工程下的資源
3.存取數據，在多個servlet間共享數據
樣例：定義一個登陸的頁面;定義一個servlet;針對成功或者失敗跳轉到不同頁面;
ServletContext在服務器啓動時,會爲託管的每一個web應用程序,創建一個ServletContext對象;從服務器移除託管或者關閉服務器時銷燬.
作用範圍:在同一個項目裏面都可以取.
獲取全局配置參數與獲取web應用中的資源的實現案例
package cw.Servlet;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;
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 Servlet06 extends HttpServlet{
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
//1.獲取全局配置參數
ServletContext context=getServletContext(); //創建對象
String rrrr=context.getInitParameter("rrrr");
System.out.println("rrrr"+"..."+rrrr);
//2.獲取web應用中的資源
/*
* 這裏如果想獲取web工程下的資源,用普通的FileInputStream寫法是不對的
* 因爲路徑不正確,這裏的相對路徑是根據jre來確定的,但是這裏是一個web工程
* jre後面由tomcat管理,所以這裏真正的相對路徑是tomcat裏的bin目錄
*/
/*
Properties pro=new Properties(); //創建屬性對象
InputStream is=new FileInputStream("src/config.properties");
pro.load(is);
String name=pro.getProperty("address");
System.out.println(name);
*/
//應該使用ServletContext
//1)第一種方式，使用getRealPath()方法,先獲取路徑再獲取流對象
ServletContext sc2=getServletContext(); //獲取ServletContext對象
String path=sc2.getRealPath("file/config.properties"); //獲取給定的文件在服務器上面的絕對路徑
Properties pro=new Properties(); //創建屬性對象
InputStream is=new FileInputStream("path");
pro.load(is);
String name=pro.getProperty("address"); //獲取address屬性的值
System.out.println(name);
is.close();
//2)第二種方式,使用getResourceAsStream(),根據相對路徑直接獲取流對象
ServletContext sc3=getServletContext();
Properties pro2=new Properties();
//獲取web工程下的資源轉換成流對象,前面隱藏當前工程的根目錄
InputStream is2=sc3.getResourceAsStream("file/config.properties");
pro2.load(is2);
String name2=pro2.getProperty("address");
System.out.println(name2);
is2.close();
//3).通過classloader(類加載器JDBC)去獲取web工程下的資源
Properties pro3=new Properties();
//獲取該java文件的class,然後獲取到加載這個class到虛擬機中的那個類加載器對象
//默認的classloader的路徑是下面這個路徑,我們必須得回到JavaWeb_1這個目錄下,才能進入file目錄
//E:\tomcat\apache-tomcat-7.0.57\wtpwebapps\JavaWeb_1\WEB-INF\classes
InputStream is3=this.getClass().getClassLoader().getResourceAsStream("../../file/config.properties");
pro3.load(is3);
String name3=pro3.getProperty("address");
System.out.println(name3);
is3.close();
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
System.out.println("bb");
}
}
實現存取數據，在多個servlet間共享數據的樣例
此功能實現了實現登陸功能，並且記錄登陸的次數返回到網頁.
login.html
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<h2>請輸入登陸信息</h2>
<form action="LoginServlet" method="get">
賬號：<input type="text" name="username" />
密碼：<input type="text" name="password" />
<input type="submit" name="登陸" />
</form>
</body>
</html>
LoginServlet.java
package cw.Servlet;
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 LoginServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/*
request：包含請求信息
response：響應數據給瀏覽器
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
//1.獲取數據
String name=request.getParameter("username");
String password=request.getParameter("password");
System.out.println("username="+name+"..."+"password="+password);
//2.校驗數據
//向客戶端輸出內容
PrintWriter pw=response.getWriter();
if("admin".equals(name)&&"123".equals(password)){
System.out.println("登陸成功");
pw.write("login success...");
//成功的次數累加
Object obj=getServletContext().getAttribute("count");//獲取以前存取的count值
Integer count=0;
if(obj!=null){
count=(Integer)obj;
}
System.out.println("已登陸成功的次數是："+count);
getServletContext().setAttribute("count", count+1);
response.setStatus(302); //設置狀態碼，重新定位目標位置
//定位跳轉的位置是哪一個頁面
response.setHeader("Location", "login_success.html"); //成功就跳轉到login_success.html
}
else{
System.out.println("登陸失敗");
pw.write("login failed...");
}
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
}
}
login_success.html
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<h2>登陸成功！</h2>
<a href="CountServlet">獲取網站登陸成功總數</a>
</body>
</html>
CountServlet.java
package cw.Servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class CountServlet
*/
public class CountServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1.取出相應的值
Integer count=(Integer)getServletContext().getAttribute("count");
//2.輸出到界面
response.getWriter().write("login success times:"+count);
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
}
}