[Java] context-param、ServletContext.getInitParameter()
這邊簡單介紹「全域初始化變數」、「取用方式」、「全域、區域、取用差別」
取用方式
xxx.java
一、程式結果
全域初始化變數：
web.xml
<context-param>
<param-name>allowed file type</param-name>
<param-value>.gif,.jpg,.bmp</param-value>
</context-param>
區域初始化變數：
web.xml
<servlet>
<init-param>
<param-name>admin</param-name>
<param-value>admin</param-value>
</init-param>
</servlet>
取用方式
全域初始化變數：
xxx.java//取得所有參數的名稱、值(型別為 ServletContext)：
ServletContext servletContext = getServletConfig().getServletContext();
//取得所有參數的名稱(型別為 Enumeration)：
Enumeration<String> params = servletContext.getInitParameterNames();
//取參數值：
String allowedFileType = servletContext.getInitParameter("allowed file type");
區域初始化變數：
xxx.java
//取所有參數的名稱、值(型別為 Enumeration)：
Enumeration<String> params = getInitParameterNames();
//取參數名：
String usernameParam = params.nextElement();
//取參數值：
String passwordParam = getInitParameter(usernameParam);
or String passwordParam = getInitParameter("admin");
一、程式結果
二、程式碼
一、程式結果
二、程式碼
Project 類型: Dynamic Web Project
Project 名稱: servlet
Package 名稱: idv.ycc.servlet
Class 類型: Servlet
Class 名稱: ContextParamServlet.java
ContextParamServlet.java
package idv.ycc.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class ContextParamServlet
*/
@WebServlet("/ContextParamServlet")
public class ContextParamServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public ContextParamServlet() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
request.setCharacterEncoding("UTF-8"); //設定request編碼
response.setCharacterEncoding("UTF-8"); //設定response編碼
response.setContentType("text/html"); //設定response內文類型
PrintWriter out = response.getWriter(); //取得response傳送字元串給client的對象
out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
out.println("<HTML>");
out.println("<HEAD><TITLE>讀取全域初始化變數</TITLE></HEAD>");
out.println("<BODY>");
out.println("<div align=center><br/>");
out.println("<fieldest style='width:90%'><legend>所有的全域初始化變數</legend><br/>");
ServletContext servletContext = getServletConfig().getServletContext(); //取得所有全域初始化變數
String uploadFolder = servletContext.getInitParameter("upload folder"); //取得全域初始化變數的值
String allowedFileType = servletContext.getInitParameter("allowed file type"); //取得全域初始化變數的值
Enumeration<String> params = servletContext.getInitParameterNames();
out.println("<div>");
out.println("<div align='left'>上傳文件夾</div>");
out.println("<div align='left''>" + uploadFolder + "</div>");
out.println("</div>");
out.println("<div>");
out.println("<div align='left'>實際磁碟路徑</div>");
out.println("<div align='left'>" + servletContext.getRealPath(uploadFolder) + "</div>");
out.println("</div>");
out.println("<div>");
out.println("<div align='left'>允許上傳的格式</div>");
out.println("<div align='left'>" + allowedFileType + "</div>");
out.println("</div>");
out.println("</fieldset></div>");
out.println("</BODY>");
out.println("</HTML>");
out.flush(); //釋放緩衝區，待滿出未釋放會出現ERROR
out.close(); //關閉PrintWriter，釋放所有系統資源
}
}
web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.1"
xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd">
<!-- 全域初始化變數 -->
<context-param>
<param-name>upload folder</param-name>
<param-value>attachment</param-value>
</context-param>
<context-param>
<param-name>allowed file type</param-name>
<param-value>.gif,.jpg,.bmp</param-value>
</context-param>
<servlet>
<servlet-name>ContextParamServlet</servlet-name>
<servlet-class>idv.ycc.servlet.ContextParamServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ContextParamServlet</servlet-name>
<url-pattern>/contextparamservlet</url-pattern>
</servlet-mapping>
</web-app>
留言
張貼留言