可以先获取项目的classPath 

String classPath = this.getClass().getResource("/").getPath();//获取classPath(部署到tomcat的路径上) 

我的为/D:/apache-tomcat-6.0.29/webapps/demo/WEB-INF/classes/  在连接下面的路径即可

代码如下:

package readproperties;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.Writer;
import java.util.Enumeration;
import java.util.Properties;

public class readProperties {
public static void main(String[] args) {
readProperty r = new readProperty();
r.read();
}


public void read(){
readProperty r = new readProperty();
r.read();
r.add();
}

}

class readProperty{
public void read(){
//readProperties rp = new readProperties();
//获取classpath
String classPath = this.getClass().getResource("/").getPath();//获取classPath(部署到tomcat的路径上)
String filepath = classPath+"readProperties/test.properties";
Properties p = new Properties();
try {
InputStream in = new BufferedInputStream(new FileInputStream(filepath));
//InputStream in = this.getClass().getClassLoader().getResourceAsStream("test.properties");
p.load(in);
//读取单个的信息


String value = http://www.mamicode.com/p.getProperty("sex");
System.out.println(value);

//读取所有的信息
Enumeration<?> en = p.propertyNames();
while(en.hasMoreElements()){
String key = (String)en.nextElement();
System.out.println(key+"==="+p.getProperty(key));
}
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}



public void add(){
String classPath = this.getClass().getResource("/").getPath();
String filepath = classPath+"readProperties/test.properties";
Properties p = new Properties();
InputStream in; //
try {
in = new BufferedInputStream(new FileInputStream(filepath));
p.load(in);
//FileOutputStream out = new FileOutputStream(new File(filepath));

Writer w = new FileWriter(new File(filepath));

p.setProperty("key2", "value2");
p.setProperty("habbit2", "ball2");
//以适合使用 load 方法加载到 Properties 表中的格式，
//将此 Properties 表中的属性列表（键和元素对）写入输出流
p.store(w, "");

} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}
}