org.apache.catalina.startup.WebappServiceLoader Maven / Gradle / Ivy
/*
* 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.
*/
package org.apache.catalina.startup;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.regex.Pattern;
import javax.servlet.ServletContext;
/**
* A variation of Java's JAR ServiceLoader that respects exclusion rules for
* web applications.
*
* Primarily intended for use loading ServletContainerInitializers as defined
* by Servlet 8.2.4. This implementation does not attempt lazy loading as the
* container is required to introspect all implementations discovered.
*
* If the ServletContext defines ORDERED_LIBS, then only JARs in WEB-INF/lib
* that are named in that set will be included in the search for
* provider configuration files; if ORDERED_LIBS is not defined then
* all JARs will be searched for provider configuration files. Providers
* defined by resources in the parent ClassLoader will always be returned.
*
* Provider classes will be loaded using the context's ClassLoader.
*
* @see javax.servlet.ServletContainerInitializer
* @see java.util.ServiceLoader
*/
public class WebappServiceLoader {
private static final String LIB = "/WEB-INF/lib/";
private static final String SERVICES = "META-INF/services/";
private static final Charset UTF8 = Charset.forName("UTF-8");
private final ServletContext context;
private final Pattern containerSciFilterPattern;
/**
* Construct a loader to load services from a ServletContext.
*
* @param context the context to use
*/
public WebappServiceLoader(ServletContext context, String containerSciFilter) {
this.context = context;
if (containerSciFilter != null && containerSciFilter.length() > 0) {
containerSciFilterPattern = Pattern.compile(containerSciFilter);
} else {
containerSciFilterPattern = null;
}
}
/**
* Load the providers for a service type.
*
* @param serviceType the type of service to load
* @return an unmodifiable collection of service providers
* @throws IOException if there was a problem loading any service
*/
public List load(Class serviceType) throws IOException {
String configFile = SERVICES + serviceType.getName();
LinkedHashSet applicationServicesFound = new LinkedHashSet();
LinkedHashSet containerServicesFound = new LinkedHashSet();
ClassLoader loader = context.getClassLoader();
// if the ServletContext has ORDERED_LIBS, then use that to specify the
// set of JARs from WEB-INF/lib that should be used for loading services
@SuppressWarnings("unchecked")
List orderedLibs =
(List) context.getAttribute(ServletContext.ORDERED_LIBS);
if (orderedLibs != null) {
// handle ordered libs directly, ...
for (String lib : orderedLibs) {
URL jarUrl = context.getResource(LIB + lib);
if (jarUrl == null) {
// should not happen, just ignore
continue;
}
String base = jarUrl.toExternalForm();
URL url;
if (base.endsWith("/")) {
url = new URL(base + configFile);
} else {
url = new URL("jar:" + base + "!/" + configFile);
}
try {
parseConfigFile(applicationServicesFound, url);
} catch (FileNotFoundException e) {
// no provider file found, this is OK
}
}
// and the parent ClassLoader for all others
loader = loader.getParent();
}
Enumeration resources;
if (loader == null) {
resources = ClassLoader.getSystemResources(configFile);
} else {
resources = loader.getResources(configFile);
}
while (resources.hasMoreElements()) {
parseConfigFile(containerServicesFound, resources.nextElement());
}
// Filter the discovered container SCIs if required
if (containerSciFilterPattern != null) {
Iterator iter = containerServicesFound.iterator();
while (iter.hasNext()) {
if (containerSciFilterPattern.matcher(iter.next()).find()) {
iter.remove();
}
}
}
// Add the application services after the container services to ensure
// that the container services are loaded first
containerServicesFound.addAll(applicationServicesFound);
// load the discovered services
if (containerServicesFound.isEmpty()) {
return Collections.emptyList();
}
return loadServices(serviceType, containerServicesFound);
}
private void parseConfigFile(LinkedHashSet servicesFound, URL url)
throws IOException {
InputStream is = null;
try {
is = url.openStream();
InputStreamReader in = new InputStreamReader(is, UTF8);
BufferedReader reader = new BufferedReader(in);
String line;
while ((line = reader.readLine()) != null) {
int i = line.indexOf('#');
if (i >= 0) {
line = line.substring(0, i);
}
line = line.trim();
if (line.length() == 0) {
continue;
}
servicesFound.add(line);
}
} finally {
if (is != null) {
is.close();
}
}
}
private List loadServices(Class serviceType, LinkedHashSet servicesFound)
throws IOException {
ClassLoader loader = context.getClassLoader();
List services = new ArrayList(servicesFound.size());
for (String serviceClass : servicesFound) {
try {
Class clazz = Class.forName(serviceClass, true, loader);
services.add(serviceType.cast(clazz.newInstance()));
} catch (ClassNotFoundException e) {
throw new IOException(e);
} catch (InstantiationException e) {
throw new IOException(e);
} catch (IllegalAccessException e) {
throw new IOException(e);
} catch (ClassCastException e) {
throw new IOException(e);
}
}
return Collections.unmodifiableList(services);
}
}