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jLo » org » jzonic » jlo » reader » ResourceLocator.java
/*
 * ResourceLocator.java
 *
 * Created on 21. Januar 2003, 21:33
 */

package org.jzonic.jlo.reader;
import java.io.*;
import java.net.URL;
import java.util.StringTokenizer;
import java.util.Vector;
/**
 * Adopted from <a href="http://www.onjava.com/pub/a/onjava/excerpt/jebp_3/index1.html?page=3">Servlet Best Practices, Part 1</a>
 * 
 * A class to locate resources, retrieve their contents, and determine their
 * last modified time. To find the resource the class searches the CLASSPATH
 * first, then Resource.class.getResource("/" + name). If the Resource finds
 * a "file:" URL, the file path will be treated as a file. Otherwise, the
 * path is treated as a URL and has limited last modified info.
 * 
 * @author Andreas Mecky <andreas.mecky@jzonic.org>
 * @author Terry Dye <terry.dye@jzonic.org>
 */
public class ResourceLocator implements Serializable {

    private String myName;
    private File myFile;
    private URL myUrl;

    /** Creates a new instance of ResourceLocator */
    public ResourceLocator() {
    }


    public ResourceLocator(String name) throws IOException {
        myName = name;
        SecurityException exception = null;

        try {
            // Search using the CLASSPATH. If found, "file" is set and the call
            // returns true.  A SecurityException might bubble up.
            if (tryClasspath(name)) {
                return;
            }
        } catch (SecurityException e) {
            exception = e; // Save for later.
        }

        try {
            // Search using the classloader getResource(  ). If found as a file,
            // "file" is set; if found as a URL, "url" is set.
            if (tryLoader(name)) {
                return;
            }
        } catch (SecurityException e) {
            exception = e; // Save for later.
        }

        // If you get here, something went wrong. Report the exception.
        String msg = "";
        if (exception != null) {
            msg = ": " + exception;
        }

        throw new IOException(
            "Resource <"
                + name
                + "> could not be found in "
                + "the CLASSPATH ("
                + System.getProperty("java.class.path")
                + "), nor could it be located by the classloader responsible for the "
                + "web application (WEB-INF/classes)"
                + msg);
    }

    /**
     * Method findResource.
     * @param fileName
     * @return InputStream
     */
    public InputStream findResource(String fileName) {
    if ( fileName == null ) {
      return null;
    }
        return getClass().getClassLoader().getResourceAsStream(fileName);
    }

    /**
     * Returns the resource name, as passed to the constructor
     */
    public String getName() {
        return myName;
    }

    /**
     * Returns an input stream to read the resource contents
     */
    public InputStream getInputStream() throws IOException {
        if (myFile != null) {
            return new BufferedInputStream(new FileInputStream(myFile));
        } else if (myUrl != null) {
            return new BufferedInputStream(myUrl.openStream());
        }
        return null;
    }

    /**
     * Returns when the resource was last modified. If the resource 
     * was found using a URL, this method will work only if the URL 
     * connection supports last modified information. If there's no 
     * support, Long.MAX_VALUE is returned. Perhaps this should return 
     * -1, but you should return MAX_VALUE on the assumption that if
     * you can't determine the time, it's maximally new.
     */
    public long lastModified() {
        if (myFile != null) {
            return myFile.lastModified();
        } else if (myUrl != null) {
            try {
                return myUrl.openConnection().getLastModified(); // Hail Mary
            } catch (IOException e) {
                return Long.MAX_VALUE;
            }
        }
        return 0; // can't happen
    }

    /**
     * Returns the directory containing the resource, or null if the 
     * resource isn't directly available on the filesystem. 
     * This value can be used to locate the configuration file on disk,
     * or to write files in the same directory.
     */
    public String getDirectory() {
        if (myFile != null) {
            return myFile.getParent();
        } else if (myUrl != null) {
            return null;
        }
        return null;
    }

    // Returns true if found
    private boolean tryClasspath(String filename) {
      if(filename == null) return false;
        String classpath = System.getProperty("java.class.path");
        String[] paths = split(classpath, File.pathSeparator);
        myFile = searchDirectories(paths, filename);
        return (myFile != null);
    }

    private static File searchDirectories(String[] paths, String filename) {
        SecurityException exception = null;
        for (int i = 0; i < paths.length; i++) {
            try {
                File file = new File(paths[i], filename);
                if (file.exists() && !file.isDirectory()) {
                    return file;
                }
            } catch (SecurityException e) {
                // Security exceptions can usually be ignored, but if all attempts
                // to find the file fail, report the (last) security exception.
                exception = e;
            }
        }
        // Couldn't find any match
        if (exception != null) {
            throw exception;
        } else {
            return null;
        }
    }

    // Splits a String into pieces according to a delimiter.
    // Uses JDK 1.1 classes for backward compatibility.
    // JDK 1.4 actually has a split(  ) method now.
    private static String[] split(String str, String delim) {
        // Use a Vector to hold the split strings.
        Vector v = new Vector();

        // Use a StringTokenizer to do the splitting.
        StringTokenizer tokenizer = new StringTokenizer(str, delim);
        while (tokenizer.hasMoreTokens()) {
            v.addElement(tokenizer.nextToken());
        }

        String[] ret = new String[v.size()];
        v.copyInto(ret);
        return ret;
    }

    // Returns true if found
    private boolean tryLoader(String name) {
        name = "/" + name;
        URL res = ResourceLocator.class.getResource(name);
        if (res == null) {
            return false;
        }

        // Try converting from a URL to a File.
        File resFile = urlToFile(res);
        if (resFile != null) {
            myFile = resFile;
        } else {
            myUrl = res;
        }
        return true;
    }

    private static File urlToFile(URL res) {
        String externalForm = res.toExternalForm();
        if (externalForm.startsWith("file:")) {
            return new File(externalForm.substring(5));
        }
        return null;
    }

    public String toString() {
        return "[Resource: File: " + myFile + " URL: " + myUrl + "]";
    }

}
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