com.bennavetta.vetinari.launch.ModuleLoader.java Source code

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Here is the source code for com.bennavetta.vetinari.launch.ModuleLoader.java

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/**
 * Copyright 2014 Ben Navetta
 *
 * Licensed 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 com.bennavetta.vetinari.launch;

import com.google.common.base.Charsets;
import com.google.common.base.Strings;
import com.google.common.base.Throwables;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterators;
import com.google.common.collect.Lists;
import com.google.common.io.Resources;
import com.google.inject.Module;
import lombok.extern.slf4j.Slf4j;

import java.io.IOException;
import java.net.URL;
import java.util.Iterator;
import java.util.List;
import java.util.stream.Collectors;

/**
 * Loads Guice modules for Vetinari. Modules are listed in {@code META-INF/vetinari-modules.txt} files. Each file
 * is UTF-8 encoded and contains a list of module class names, one on each line. Empty lines and lines starting
 * with {@code #} are ignored. Module classes must have no-argument constructors.
 */
@Slf4j
public class ModuleLoader {
    private List<URL> findListingFiles(ClassLoader classLoader) throws IOException {
        Iterator<URL> iter = Iterators.forEnumeration(classLoader.getResources("META-INF/vetinari-modules.txt"));
        return Lists.newArrayList(iter);
    }

    private List<String> parseListing(URL listingUrl) throws IOException {
        return Resources.readLines(listingUrl, Charsets.UTF_8).stream().map(String::trim)
                .filter(l -> !l.startsWith("#")).filter(l -> !Strings.isNullOrEmpty(l))
                .collect(Collectors.toList());
    }

    /**
     * Loads Guice modules from the classpath as described above.
     * @throws IOException if thrown reading classpath resources
     */
    public List<Module> loadModules() throws IOException {
        List<String> classNames = Lists.newArrayList();
        for (URL listing : findListingFiles(getClass().getClassLoader())) {
            log.debug("Reading module list from {}", listing);
            classNames.addAll(parseListing(listing));
        }

        ImmutableList.Builder<Module> modulesBuilder = ImmutableList.builder();
        try {
            for (String className : classNames) {
                log.debug("Instantiating module class {}", className);
                modulesBuilder.add((Module) Class.forName(className).newInstance());
            }
        } catch (ClassNotFoundException | InstantiationException | IllegalAccessException e) {
            throw Throwables.propagate(e); // Something is probably wrong with the setup if this happens.
        }

        return modulesBuilder.build();
    }
}