WebappServiceLoader.java
/*
* 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.URI;
import java.net.URISyntaxException;
import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
import java.util.regex.Pattern;
import javax.servlet.ServletContext;
import org.apache.catalina.Context;
import org.apache.tomcat.util.scan.JarFactory;
/**
* A variation of Java's JAR ServiceLoader that respects exclusion rules for web applications.
* <p>
* 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.
* <p>
* 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.
* <p>
* Provider classes will be loaded using the context's ClassLoader.
*
* @param <T> The type of service to load
*
* @see javax.servlet.ServletContainerInitializer
* @see java.util.ServiceLoader
*/
public class WebappServiceLoader<T> {
private static final String CLASSES = "/WEB-INF/classes/";
private static final String LIB = "/WEB-INF/lib/";
private static final String SERVICES = "META-INF/services/";
private final Context context;
private final ServletContext servletContext;
private final Pattern containerSciFilterPattern;
/**
* Construct a loader to load services from a ServletContext.
*
* @param context the context to use
*/
public WebappServiceLoader(Context context) {
this.context = context;
this.servletContext = context.getServletContext();
String containerSciFilter = context.getContainerSciFilter();
if (containerSciFilter != null && containerSciFilter.length() > 0) {
containerSciFilterPattern = Pattern.compile(containerSciFilter);
} else {
containerSciFilterPattern = null;
}
}
/**
* Load the providers for a service type. Container defined services will be loaded before application defined
* services in case the application depends on a Container provided service. Note that services are always loaded
* via the Context (web application) class loader so it is possible for an application to provide an alternative
* implementation of what would normally be a Container provided service.
*
* @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<T> load(Class<T> serviceType) throws IOException {
String configFile = SERVICES + serviceType.getName();
// Obtain the Container provided service configuration files.
ClassLoader loader = context.getParentClassLoader();
Enumeration<URL> containerResources;
if (loader == null) {
containerResources = ClassLoader.getSystemResources(configFile);
} else {
containerResources = loader.getResources(configFile);
}
// Extract the Container provided service class names. Each
// configuration file may list more than one service class name. This
// uses a LinkedHashSet so if a service class name appears more than
// once in the configuration files, only the first one found is used.
LinkedHashSet<String> containerServiceClassNames = new LinkedHashSet<>();
Set<URL> containerServiceConfigFiles = new HashSet<>();
while (containerResources.hasMoreElements()) {
URL containerServiceConfigFile = containerResources.nextElement();
containerServiceConfigFiles.add(containerServiceConfigFile);
parseConfigFile(containerServiceClassNames, containerServiceConfigFile);
}
// Filter the discovered container SCIs if required
if (containerSciFilterPattern != null) {
Iterator<String> iter = containerServiceClassNames.iterator();
while (iter.hasNext()) {
if (containerSciFilterPattern.matcher(iter.next()).find()) {
iter.remove();
}
}
}
// Obtaining the application provided configuration files is a little
// more difficult for two reasons:
// - The web application may employ a custom class loader. Ideally, we
// would use ClassLoader.findResources() but that method is protected.
// We could force custom class loaders to override that method and
// make it public but that would be a new requirement and break
// backwards compatibility for what is an often customised component.
// - If the application web.xml file has defined an order for fragments
// then only those JAR files represented by fragments in that order
// (and arguably WEB-INF/classes) should be scanned for services.
LinkedHashSet<String> applicationServiceClassNames = new LinkedHashSet<>();
// Check to see if the ServletContext has ORDERED_LIBS defined
@SuppressWarnings("unchecked")
List<String> orderedLibs = (List<String>) servletContext.getAttribute(ServletContext.ORDERED_LIBS);
// Obtain the application provided service configuration files
if (orderedLibs == null) {
// Because a custom class loader may be being used, we have to use
// getResources() which will return application and Container files.
Enumeration<URL> allResources = servletContext.getClassLoader().getResources(configFile);
while (allResources.hasMoreElements()) {
URL serviceConfigFile = allResources.nextElement();
// Only process the service configuration file if it is not a
// Container level file that has already been processed
if (!containerServiceConfigFiles.contains(serviceConfigFile)) {
parseConfigFile(applicationServiceClassNames, serviceConfigFile);
}
}
} else {
// Ordered libs so only use services defined in those libs and any
// in WEB-INF/classes
URL unpacked = servletContext.getResource(CLASSES + configFile);
if (unpacked != null) {
parseConfigFile(applicationServiceClassNames, unpacked);
}
for (String lib : orderedLibs) {
URL jarUrl = servletContext.getResource(LIB + lib);
if (jarUrl == null) {
// should not happen, just ignore
continue;
}
String base = jarUrl.toExternalForm();
URL url;
if (base.endsWith("/")) {
URI uri;
try {
uri = new URI(base + configFile);
} catch (URISyntaxException e) {
// Not ideal but consistent with public API
throw new IOException(e);
}
url = uri.toURL();
} else {
url = JarFactory.getJarEntryURL(jarUrl, configFile);
}
try {
parseConfigFile(applicationServiceClassNames, url);
} catch (FileNotFoundException e) {
// no provider file found, this is OK
}
}
}
// Add the application services after the container services to ensure
// that the container services are loaded first
containerServiceClassNames.addAll(applicationServiceClassNames);
// Short-cut if no services have been found
if (containerServiceClassNames.isEmpty()) {
return Collections.emptyList();
}
// Load the discovered services
return loadServices(serviceType, containerServiceClassNames);
}
void parseConfigFile(LinkedHashSet<String> servicesFound, URL url) throws IOException {
try (InputStream is = url.openStream();
InputStreamReader in = new InputStreamReader(is, StandardCharsets.UTF_8);
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);
}
}
}
List<T> loadServices(Class<T> serviceType, LinkedHashSet<String> servicesFound) throws IOException {
ClassLoader loader = servletContext.getClassLoader();
List<T> services = new ArrayList<>(servicesFound.size());
for (String serviceClass : servicesFound) {
try {
Class<?> clazz = Class.forName(serviceClass, true, loader);
services.add(serviceType.cast(clazz.getConstructor().newInstance()));
} catch (ReflectiveOperationException | ClassCastException e) {
throw new IOException(e);
}
}
return Collections.unmodifiableList(services);
}
}