jsp application使用getInitParameter来获取web.xml中配置参数

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jsp中9个内置对象之一application，它的数据对整个web应用都有效，application有一个重要的用途就是获取web.xm中的配置参数，这样可以提高代码的移植性。应用案例如下：

在web.xml中配置如下代码：

  <context-param>
  <param-name>driver</param-name>
  <param-value>com.mysql.jdbc.Driver</param-value>
  </context-param>
  <context-param>
  <param-name>url</param-name>
  <param-value>jdbc:mysql://localhost:3307/test</param-value>
  </context-param>
  <context-param>
  <param-name>user</param-name>
  <param-value>root</param-value>
  </context-param>
  <context-param>
  <param-name>pass</param-name>
  <param-value>root</param-value>
  </context-param>

然后在需要使用参数的页面通过getInitParameter()来获取：

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<%@ page import="java.sql.*" %>
<!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>
<table border="1">
<tr><th>编号<th>用户名</th><th>密码</th></tr>
<% 
String driver = application.getInitParameter("driver");
String url = application.getInitParameter("url");
String user = application.getInitParameter("user");
String pass = application.getInitParameter("pass");
Class.forName(driver);
Connection conn = DriverManager.getConnection(url, user, pass);
Statement stmt = conn.createStatement();
String sql = "select * from user";
ResultSet rs = stmt.executeQuery(sql);
while(rs.next()){
%>
<tr><td><%=rs.getString(1)%></td><td><%=rs.getString(2)%></td><td><%=rs.getString(3)%></td></tr>
<%
}
%>
</table>
</body>
</html>

重启tomcat后，参数才起效，可以看到结果：

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