io.opencensus.contrib.agent.Resources.java Source code

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Here is the source code for io.opencensus.contrib.agent.Resources.java

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/*
 * Copyright 2017, Google Inc.
 * 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 io.opencensus.contrib.agent;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Strings;
import com.google.common.io.ByteStreams;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

/**
 * Helper methods for working with resources.
 */
final class Resources {

    /**
     * Returns a resource of the given name as a temporary file.
     *
     * @param resourceName name of the resource
     * @return a temporary {@link File} containing a copy of the resource
     * @throws FileNotFoundException if no resource of the given name is found
     * @throws IOException if an I/O error occurs
     */
    static File getResourceAsTempFile(String resourceName) throws IOException {
        checkArgument(!Strings.isNullOrEmpty(resourceName), "resourceName");

        File file = File.createTempFile(resourceName, ".tmp");
        try (OutputStream os = new FileOutputStream(file)) {
            getResourceAsTempFile(resourceName, file, os);
            return file;
        }
    }

    @VisibleForTesting
    static void getResourceAsTempFile(String resourceName, File file, OutputStream outputStream)
            throws IOException {
        checkArgument(!Strings.isNullOrEmpty(resourceName), "resourceName");
        checkNotNull(file, "file");
        checkNotNull(outputStream, "outputStream");

        file.deleteOnExit();

        try (InputStream is = getResourceAsStream(resourceName)) {
            ByteStreams.copy(is, outputStream);
        }
    }

    private static InputStream getResourceAsStream(String resourceName) throws FileNotFoundException {
        checkArgument(!Strings.isNullOrEmpty(resourceName), "resourceName");

        InputStream is = Resources.class.getResourceAsStream(resourceName);
        if (is == null) {
            throw new FileNotFoundException("Cannot find resource '" + resourceName + "' on the class path.");
        }
        return is;
    }
}