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java/org/apache/catalina/startup/WebappServiceLoader.java
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java/org/apache/catalina/startup/WebappServiceLoader.java
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/*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.apache.catalina.startup;
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import java.io.BufferedReader;
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import java.io.FileNotFoundException;
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import java.io.IOException;
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import java.io.InputStream;
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import java.io.InputStreamReader;
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import java.net.URL;
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import java.nio.charset.StandardCharsets;
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import java.util.ArrayList;
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import java.util.Collections;
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import java.util.Enumeration;
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import java.util.Iterator;
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import java.util.LinkedHashSet;
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import java.util.List;
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import java.util.regex.Pattern;
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import javax.servlet.ServletContext;
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import org.apache.catalina.Context;
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import org.apache.catalina.WebResource;
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import org.apache.tomcat.util.scan.JarFactory;
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/**
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* A variation of Java's JAR ServiceLoader that respects exclusion rules for
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* web applications.
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* <p>
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* Primarily intended for use loading ServletContainerInitializers as defined
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* by Servlet 8.2.4. This implementation does not attempt lazy loading as the
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* container is required to introspect all implementations discovered.
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* <p>
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* If the ServletContext defines ORDERED_LIBS, then only JARs in WEB-INF/lib
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* that are named in that set will be included in the search for
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* provider configuration files; if ORDERED_LIBS is not defined then
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* all JARs will be searched for provider configuration files. Providers
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* defined by resources in the parent ClassLoader will always be returned.
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* <p>
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* Provider classes will be loaded using the context's ClassLoader.
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*
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* @param <T> The type of service to load
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*
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* @see javax.servlet.ServletContainerInitializer
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* @see java.util.ServiceLoader
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*/
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public class WebappServiceLoader<T> {
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private static final String CLASSES = "/WEB-INF/classes/";
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private static final String LIB = "/WEB-INF/lib/";
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private static final String SERVICES = "META-INF/services/";
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private final Context context;
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private final ServletContext servletContext;
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private final Pattern containerSciFilterPattern;
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/**
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* Construct a loader to load services from a ServletContext.
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*
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* @param context the context to use
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*/
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public WebappServiceLoader(Context context) {
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this.context = context;
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this.servletContext = context.getServletContext();
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String containerSciFilter = context.getContainerSciFilter();
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if (containerSciFilter != null && containerSciFilter.length() > 0) {
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containerSciFilterPattern = Pattern.compile(containerSciFilter);
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} else {
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containerSciFilterPattern = null;
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}
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}
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/**
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* Load the providers for a service type.
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*
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* @param serviceType the type of service to load
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* @return an unmodifiable collection of service providers
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* @throws IOException if there was a problem loading any service
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*/
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public List<T> load(Class<T> serviceType) throws IOException {
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String configFile = SERVICES + serviceType.getName();
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LinkedHashSet<String> applicationServicesFound = new LinkedHashSet<>();
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LinkedHashSet<String> containerServicesFound = new LinkedHashSet<>();
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// if the ServletContext has ORDERED_LIBS, then use that to specify the
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// set of JARs from WEB-INF/lib that should be used for loading services
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@SuppressWarnings("unchecked")
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List<String> orderedLibs = (List<String>) servletContext.getAttribute(ServletContext.ORDERED_LIBS);
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// Handle application SCIs directly...
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if (orderedLibs == null) {
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// No ordered libs, so use every service definition we can find
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WebResource[] resources = context.getResources().getClassLoaderResources("/" + configFile);
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for (WebResource resource : resources) {
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if (resource.isFile()) {
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parseConfigFile(applicationServicesFound, resource.getURL());
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}
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}
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} else {
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// Ordered libs so only use services defined in those libs and any
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// in WEB-INF/classes
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URL unpacked = servletContext.getResource(CLASSES + configFile);
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if (unpacked != null) {
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parseConfigFile(applicationServicesFound, unpacked);
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}
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for (String lib : orderedLibs) {
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URL jarUrl = servletContext.getResource(LIB + lib);
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if (jarUrl == null) {
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// should not happen, just ignore
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continue;
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}
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String base = jarUrl.toExternalForm();
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URL url;
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if (base.endsWith("/")) {
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url = new URL(base + configFile);
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} else {
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url = JarFactory.getJarEntryURL(jarUrl, configFile);
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}
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try {
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parseConfigFile(applicationServicesFound, url);
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} catch (FileNotFoundException e) {
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// no provider file found, this is OK
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}
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}
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}
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// and use the parent ClassLoader for all other SCIs
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ClassLoader loader = context.getParentClassLoader();
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Enumeration<URL> resources;
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if (loader == null) {
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resources = ClassLoader.getSystemResources(configFile);
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} else {
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resources = loader.getResources(configFile);
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}
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while (resources.hasMoreElements()) {
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parseConfigFile(containerServicesFound, resources.nextElement());
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}
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// Filter the discovered container SCIs if required
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if (containerSciFilterPattern != null) {
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Iterator<String> iter = containerServicesFound.iterator();
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while (iter.hasNext()) {
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if (containerSciFilterPattern.matcher(iter.next()).find()) {
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iter.remove();
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}
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}
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}
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// Add the application services after the container services to ensure
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// that the container services are loaded first
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containerServicesFound.addAll(applicationServicesFound);
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// load the discovered services
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if (containerServicesFound.isEmpty()) {
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return Collections.emptyList();
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}
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return loadServices(serviceType, containerServicesFound);
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}
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void parseConfigFile(LinkedHashSet<String> servicesFound, URL url)
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throws IOException {
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try (InputStream is = url.openStream();
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InputStreamReader in = new InputStreamReader(is, StandardCharsets.UTF_8);
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BufferedReader reader = new BufferedReader(in)) {
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String line;
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while ((line = reader.readLine()) != null) {
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int i = line.indexOf('#');
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if (i >= 0) {
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line = line.substring(0, i);
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}
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line = line.trim();
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if (line.length() == 0) {
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continue;
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}
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servicesFound.add(line);
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}
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}
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}
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List<T> loadServices(Class<T> serviceType, LinkedHashSet<String> servicesFound)
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throws IOException {
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ClassLoader loader = servletContext.getClassLoader();
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List<T> services = new ArrayList<>(servicesFound.size());
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for (String serviceClass : servicesFound) {
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try {
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Class<?> clazz = Class.forName(serviceClass, true, loader);
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services.add(serviceType.cast(clazz.getConstructor().newInstance()));
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} catch (ReflectiveOperationException | ClassCastException e) {
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throw new IOException(e);
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}
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}
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return Collections.unmodifiableList(services);
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}
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}
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