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);