DZone Snippets: classpath code

Printing out the full path of a resource on the classpath

Archanciel (Jean-Pierre Schnyder) — Tue, 04 Sep 2007 09:59:44 GMT

// displaying the full path of a resource found by the class loader on the classpath, here the log4j.xml file



String resourceName = "/log4j.xml"; // pay attention to the leading '/' !

URL location = AnyClass.class.getResource(resourceName);



if (location != null) {

    System.out.println(location.getPath());

} else {

    System.out.println(resourceName + " not found on the classpath");

}

Loading a text file into a String from the classpath

Archanciel (Jean-Pierre Schnyder) — Thu, 30 Aug 2007 12:48:18 GMT

Locate a text file in the classpath and read it into a String



    /** 

     * @param filePath      name of file to open. The file can reside

     *                      anywhere in the classpath

     */

    private String readFileAsString(String filePath) throws java.io.IOException {

        StringBuffer fileData = new StringBuffer(1000);

        BufferedReader reader = new BufferedReader(new InputStreamReader(this

            .getClass().getClassLoader().getResourceAsStream(filePath)));

        char[] buf = new char[1024];

        int numRead = 0;

        while ((numRead = reader.read(buf)) != -1) {

            String readData = String.valueOf(buf, 0, numRead);

            fileData.append(readData);

            buf = new char[1024];

        }

        reader.close();

        return fileData.toString();

    }

Loading a property file from the classpath

Archanciel (Jean-Pierre Schnyder) — Thu, 30 Aug 2007 12:28:02 GMT

Loads a property file located anywhere in the classpath



    private Properties getPropertiesFromClasspath(String propFileName) throws IOException {

        // loading xmlProfileGen.properties from the classpath

        Properties props = new Properties();

        InputStream inputStream = this.getClass().getClassLoader()

            .getResourceAsStream(propFileName);



        if (inputStream == null) {

            throw new FileNotFoundException("property file '" + propFileName

                + "' not found in the classpath");

        }



        props.load(inputStream);



        return props;

    }

Add a jar file to Java load path at run time

mikewilsonuk (Mike Wilson) — Fri, 23 Feb 2007 15:24:18 GMT

Sometimes it is necessary to amend the class load path at run time. For example, dynamically adding jar files containing user-configurable JDBC data sources. The way this is done is truly monstrous -- the URL Path format was only revealed when a colleague looked into the Java library sources.



import java.net.URL;

import java.io.IOException;

import java.net.URLClassLoader;

import java.net.MalformedURLException;



public class JarFileLoader extends URLClassLoader

{

    public JarFileLoader (URL[] urls)

    {

        super (urls);

    }



    public void addFile (String path) throws MalformedURLException

    {

        String urlPath = "jar:file://" + path + "!/";

        addURL (new URL (urlPath));

    }



    public static void main (String args [])

    {

        try

        {

            System.out.println ("First attempt...");

            Class.forName ("org.gjt.mm.mysql.Driver");

        }

        catch (Exception ex)

        {

            System.out.println ("Failed.");

        }



        try

        {

            URL urls [] = {};



            JarFileLoader cl = new JarFileLoader (urls);

            cl.addFile ("/opt/mysql-connector-java-5.0.4/mysql-connector-java-5.0.4-bin.jar");

            System.out.println ("Second attempt...");

            cl.loadClass ("org.gjt.mm.mysql.Driver");

            System.out.println ("Success!");

        }

        catch (Exception ex)

        {

            System.out.println ("Failed.");

            ex.printStackTrace ();

        }

    }

}