方式一：採用ServletContext讀取

獲取配置檔案的realpath，然後通過檔案流讀取出來或者通過方法getReasurceAsStream()。

因為是用ServletContext讀取檔案路徑，所以配置檔案可以放入在WEB-INF的classes目錄中，也可以在應用層級及WEB-INF的目錄中。檔案存放位置具體在eclipse工程中的表現是：可以放在src下面，也可放在WEB-INF及Web-Root下面等。因為是讀取出路徑後，用檔案流進行讀取的，所以可以讀取任意的配置檔案包括xml和properties。缺點：不能在servlet外面應用讀取配置資訊。

1.首先建立一個動態的javaweb專案，專案目錄如下：

2.建立一個servlet（FileReader.java）

package com.xia.fileReader;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
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 FileReader extends HttpServlet {
	private static final long serialVersionUID = 1L;
  

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		
		 /**
         * response.setContentType("text/html;charset=UTF-8");目的是控制瀏覽器用UTF-8進行解碼；
         * 這樣就不會出現中文亂碼了
         */
        response.setHeader("content-type","text/html;charset=UTF-8");
        readSrcDirPropCfgFile(response);//讀取src目錄下的db1.properties配置檔案
        response.getWriter().println("<hr/>");
        readWebRootDirPropCfgFile(response);//讀取WebRoot目錄下的db2.properties配置檔案
        response.getWriter().println("<hr/>");
        readSrcSourcePackPropCfgFile(response);//讀取src目錄下的config目錄中的db3.properties配置檔案
        response.getWriter().println("<hr/>");
        readWEBINFPropCfgFile(response);//讀取WEB-INF目錄下的JDBC目錄中的db4.properties配置檔案
		
	}
	public void readSrcDirPropCfgFile(HttpServletResponse response) throws IOException {
		String path = "/WEB-INF/classes/db1.properties";
		InputStream in = this.getServletContext().getResourceAsStream(path);
	    Properties props = new Properties();
	    props.load(in);
	    String driver = props.getProperty("jdbc.driver");
	    String url = props.getProperty("jdbc.url");
	    String username = props.getProperty("jdbc.username");
	    String password = props.getProperty("jdbc.password");
	    response.getWriter().println("讀取src目錄下的db1.properties配置檔案");
	    response.getWriter().println(MessageFormat.format( "driver={0},url={1},username={2},password={3}", 
                driver,url, username, password));
	}
	public void readWebRootDirPropCfgFile(HttpServletResponse response) throws IOException{
		String path = "/db2.properties";
		InputStream in = this.getServletContext().getResourceAsStream(path);
	    Properties props = new Properties();
	    props.load(in);
	    String driver = props.getProperty("jdbc.driver");
	    String url = props.getProperty("jdbc.url");
	    String username = props.getProperty("jdbc.username");
	    String password = props.getProperty("jdbc.password");
	    response.getWriter().println("讀取WebRoot目錄下的db2.properties配置檔案");
	    response.getWriter().println(MessageFormat.format( "driver={0},url={1},username={2},password={3}", 
                driver,url, username, password));
	}
	public void readSrcSourcePackPropCfgFile(HttpServletResponse response) throws IOException {
		String path = "/WEB-INF/classes/config/db3.properties";
		String realPath = this.getServletContext().getRealPath(path);
	    InputStreamReader reader = new InputStreamReader(new FileInputStream(realPath),"UTF-8");
	    Properties props = new Properties();
	    props.load(reader);
	    String driver = props.getProperty("jdbc.driver");
	    String url = props.getProperty("jdbc.url");
	    String username = props.getProperty("jdbc.username");
	    String password = props.getProperty("jdbc.password");
	    response.getWriter().println("讀取src目錄下的config目錄中的db3.properties配置檔案");
	    response.getWriter().println(MessageFormat.format( "driver={0},url={1},username={2},password={3}", 
                driver,url, username, password));
	}
		
		public void readWEBINFPropCfgFile(HttpServletResponse response) throws IOException {
		String path = "/WEB-INF/JDBC/db4.properties";
		String realPath = this.getServletContext().getRealPath(path);
	    System.out.println("realPath："+realPath);
	    System.out.println("contextPath："+this.getServletContext().getContextPath());
	    InputStreamReader reader = new InputStreamReader(new FileInputStream(realPath),"UTF-8");
	    Properties props = new Properties();
	    props.load(reader);
	    String driver = props.getProperty("jdbc.driver");
	    String url = props.getProperty("jdbc.url");
	    String username = props.getProperty("jdbc.username");
	    String password = props.getProperty("jdbc.password");
	    response.getWriter().println("讀取WEB-INF目錄下的JDBC目錄中的db4.properties配置檔案");
	    response.getWriter().println(MessageFormat.format( "driver={0},url={1},username={2},password={3}", 
                driver,url, username, password));
	}

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

}
 

3.配置servlet（web.xml）

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>javaReaderFile</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  
  <servlet>
    <servlet-name>FileReader</servlet-name>
    <servlet-class>com.xia.fileReader.FileReader</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>FileReader</servlet-name>
    <url-pattern>/FileReader</url-pattern>
  </servlet-mapping>
</web-app>
 

方式二：採用ResourceBundle類讀取配置資訊

優點是：可以以完全限定類名的方式載入資源後，直接的讀取出來，且可以在非Web應用中讀取資原始檔。

缺點：只能載入類src下面的資原始檔且只能讀取.properties檔案。

1. /** 
2.  * 獲取指定配置檔案中所有的資料 
3.  * @param propertyName 
4.  *        呼叫方式： 
5.  *            1.配置檔案放在resource源包下，不用加字尾 
6.  *              PropertiesUtil.getAllMessage("message"); 
7.  *            2.放在包裡面的 
8.  *              PropertiesUtil.getAllMessage("com.test.message"); 
9.  * @return 
10.  */
11. publicstatic List<String> getAllMessage(String propertyName) {  
12.     // 獲得資源包
13.     ResourceBundle rb = ResourceBundle.getBundle(propertyName.trim());  
14.     // 通過資源包拿到所有的key
15.     Enumeration<String> allKey = rb.getKeys();  
16.     // 遍歷key 得到 value
17.     List<String> valList = new ArrayList<String>();  
18.     while (allKey.hasMoreElements()) {  
19.         String key = allKey.nextElement();  
20.         String value = (String) rb.getString(key);  
21.         valList.add(value);  
22.     }  
23.     return valList;  
24. }  

方式三：採用ClassLoader方式進行讀取配置資訊

package com.xia.fileReader;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Properties;

public class ReadByClassLoader {

	public static void main(String[] args) throws IOException {
		readPropFileByClassLoad();
	}

	 public static void readPropFileByClassLoad() throws IOException{
		 //讀取src下面config包內的配置檔案db3.properties
		 InputStream in = ReadByClassLoader.class.getClassLoader().getResourceAsStream("config/db3.properties");
		 BufferedReader br = new BufferedReader(new InputStreamReader(in));
		 Properties props = new Properties();
		 props.load(br);
		 for(Object s: props.keySet()){
			 System.out.println(s+":"+props.getProperty(s.toString()));
		 }
	 }
}

方式四： PropertiesLoaderUtils工具類