Java tutorial
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/* $Id$ */
import java.io.IOException;
import java.net.URL;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.Vector;
import java.util.jar.Attributes;
import java.util.jar.Manifest;
/**
* A class to find resources in the classpath by their mime-type specified in
* the MANIFEST.
* <p>
* This class searches for content entries in all META-INF/MANIFEST.MF files. It
* will find files with a given Content-Type: attribute. This allows to add
* arbitrary resources by content-type just by creating a JAR wrapper and adding
* them to the classpath.
* <p>
* Example:<br>
*
* <pre>
* Name: test.txt
* Content-Type: text/plain
* </pre>
*/
public final class ClasspathResource {
/**
* Actual Type: Map<String,List<URL>>.
*/
private final Map contentMappings;
private static final String MANIFEST_PATH = "META-INF/MANIFEST.MF";
private static final String CONTENT_TYPE_KEY = "Content-Type";
private static ClasspathResource classpathResource;
private ClasspathResource() {
contentMappings = new HashMap();
loadManifests();
}
/**
* Retrieve the singleton instance of this class.
*
* @return the ClassPathResource instance.
*/
public static synchronized ClasspathResource getInstance() {
if (classpathResource == null) {
classpathResource = new ClasspathResource();
}
return classpathResource;
}
/* Actual return type: Set<ClassLoader> */
private Set getClassLoadersForResources() {
Set v = new HashSet();
try {
ClassLoader l = ClassLoader.getSystemClassLoader();
if (l != null) {
v.add(l);
}
} catch (SecurityException e) {
// Ignore
}
try {
ClassLoader l = Thread.currentThread().getContextClassLoader();
if (l != null) {
v.add(l);
}
} catch (SecurityException e) {
// Ignore
}
try {
ClassLoader l = ClasspathResource.class.getClassLoader();
if (l != null) {
v.add(l);
}
} catch (SecurityException e) {
// Ignore
}
return v;
}
private void loadManifests() {
Enumeration e;
try {
Iterator it = getClassLoadersForResources().iterator();
while (it.hasNext()) {
ClassLoader classLoader = (ClassLoader) it.next();
e = classLoader.getResources(MANIFEST_PATH);
while (e.hasMoreElements()) {
final URL u = (URL) e.nextElement();
try {
final Manifest manifest = new Manifest(u.openStream());
final Map entries = manifest.getEntries();
final Iterator entrysetiterator = entries.entrySet().iterator();
while (entrysetiterator.hasNext()) {
final Map.Entry entry = (Map.Entry) entrysetiterator.next();
final String name = (String) entry.getKey();
final Attributes attributes = (Attributes) entry.getValue();
final String contentType = attributes.getValue(CONTENT_TYPE_KEY);
if (contentType != null) {
addToMapping(contentType, name, classLoader);
}
}
} catch (IOException io) {
// TODO: Log.
}
}
}
} catch (IOException io) {
// TODO: Log.
}
}
private void addToMapping(final String contentType, final String name, final ClassLoader classLoader) {
List existingFiles = (List) contentMappings.get(contentType);
if (existingFiles == null) {
existingFiles = new Vector();
contentMappings.put(contentType, existingFiles);
}
final URL url = classLoader.getResource(name);
if (url != null) {
existingFiles.add(url);
}
}
/**
* Retrieve a list of resources known to have the given mime-type.
*
* @param mimeType
* the mime-type to search for.
* @return a List<URL>, guaranteed to be != null.
*/
public List listResourcesOfMimeType(final String mimeType) {
final List content = (List) contentMappings.get(mimeType);
if (content == null) {
return Collections.EMPTY_LIST;
} else {
return content;
}
}
}
////////////////
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/* $Id: $ */
package org.apache.xmlgraphics.util;
import java.net.URL;
import java.util.Iterator;
import java.util.List;
import junit.framework.TestCase;
/**
* Test for the Service class.
*/
public class ClasspathResourceTest extends TestCase {
/**
* Tests whether the file /sample.txt with mime-type text/plain exists.
*
* @throws Exception
* in case of an error
*/
public void testSampleResource() throws Exception {
final List list = ClasspathResource.getInstance().listResourcesOfMimeType("text/plain");
boolean found = false;
final Iterator i = list.iterator();
while (i.hasNext()) {
final URL u = (URL) i.next();
if (u.getPath().endsWith("sample.txt")) {
found = true;
}
}
assertTrue(found);
}
/**
* Tests the mode where Service returns class names.
*
* @throws Exception
* in case of an error
*/
public void testNonexistingResource() throws Exception {
final List list = ClasspathResource.getInstance().listResourcesOfMimeType("nota/mime-type");
assertTrue(list.isEmpty());
}
}