a=testA

b:testB

package properties;

import java.io.BufferedInputStream;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.IOException;

import java.io.InputStream;

import java.util.Enumeration;

import java.util.Properties;

public class PropertiesManipulate {

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

        readProperties();

        readSystemProperties();

    }

    private static void readSystemProperties() {

        Properties props = System.getProperties();

        Enumeration<?> prop_names = props.propertyNames();

        while (prop_names.hasMoreElements()) {

            String prop_name = (String) prop_names.nextElement();

            String property = props.getProperty(prop_name);

            System.out.println("Property \"" + prop_name + "\" is \"" + property

                    + "\"");

        }

    }

    private static void readProperties() throws FileNotFoundException,

            IOException {

        String name = "test.properties";

        InputStream in = new BufferedInputStream(new FileInputStream(name));

        Properties p = new Properties();

        p.load(in);

        System.out.println("a==>" + p.getProperty("a"));

    }

}

a==>testA

Property "java.runtime.name" is "Java(TM) SE Runtime Environment"
...（omit）

System.setProperties(props);