Hadoop Configuration Property Returns Null

问题:

I wrote a simple code to test how to set configuration in Hadoop.

public static void main(String[] args) {

        Configuration conf = new Configuration();
        conf.addResource("~/conf.xml");
        System.out.println(conf);
        System.out.println(conf.get("color"));
}

The output of above program is:

Configuration: core-default.xml, core-site.xml, ~/conf.xml
null

Thus conf.get("color") returns null. However, I have explicitly set that property in conf.xml as follows:

<property>
        <name>color</name>
        <value>yellow</value>
        <description>Color</description>
</property>

回答1:

The resource needs to be added as a URL, otherwise the String is interpreted as a classpath resource (which at the moment does not resolve and is ignored - i know you you think that a warn message would be dumped somewhere):

/**
 * Add a configuration resource. 
 * 
 * The properties of this resource will override properties of previously 
 * added resources, unless they were marked <a href="#Final">final</a>. 
 * 
 * @param name resource to be added, the classpath is examined for a file 
 *             with that name.
 */
public void addResource(String name) {
  addResourceObject(name);
}

Anyway, try this (i get yellow in the syserr):

@Test
public void testConf() throws MalformedURLException {
    Configuration conf = new Configuration();

    conf.addResource(new File("~/conf.xml")
            .getAbsoluteFile().toURI().toURL());
    conf.reloadConfiguration();
    System.err.println(conf);

    System.err.println(conf.get("color"));
}