juneau-core/juneau-config/src/main/java/org/apache/juneau/config/store/ConfigClasspathStore.java

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// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
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package org.apache.juneau.config.store;

import static org.apache.juneau.internal.StringUtils.*;

import java.io.*;
import java.util.concurrent.*;

import org.apache.juneau.*;
import org.apache.juneau.annotation.*;
import org.apache.juneau.internal.*;

/**
 * Classpath-based storage location for configuration files.
 *
 * <p>
 * Looks inside the JVM classpath for configuration files.
 *
 * <p>
 * Configuration files retrieved from the classpath can be modified but not persisted.
 */
@ConfigurableContext
public class ConfigClasspathStore extends ConfigStore {

	//-------------------------------------------------------------------------------------------------------------------
	// Configurable properties
	//-------------------------------------------------------------------------------------------------------------------

	static final String PREFIX = "ConfigClasspathStore";

	//-------------------------------------------------------------------------------------------------------------------
	// Predefined instances
	//-------------------------------------------------------------------------------------------------------------------

	/** Default memory store, all default values.*/
	public static final ConfigClasspathStore DEFAULT = ConfigClasspathStore.create().build();


	//-------------------------------------------------------------------------------------------------------------------
	// Instance
	//-------------------------------------------------------------------------------------------------------------------

	/**
	 * Create a new builder for this object.
	 *
	 * @return A new builder for this object.
	 */
	public static ConfigClasspathStoreBuilder create() {
		return new ConfigClasspathStoreBuilder();
	}

	@Override /* Context */
	public ConfigClasspathStoreBuilder builder() {
		return new ConfigClasspathStoreBuilder(getPropertyStore());
	}

	private final ConcurrentHashMap<String,String> cache = new ConcurrentHashMap<>();

	/**
	 * Constructor.
	 *
	 * @param ps The settings for this content store.
	 */
	protected ConfigClasspathStore(PropertyStore ps) {
		super(ps);
	}

	@Override /* ConfigStore */
	public synchronized String read(String name) throws IOException {
		String s = cache.get(name);
		if (s != null)
			return s;

		ClassLoader cl = Thread.currentThread().getContextClassLoader();
		try (InputStream in = cl.getResourceAsStream(name)) {
			if (in != null)
				cache.put(name, IOUtils.read(in, IOUtils.UTF8));
		}
		return emptyIfNull(cache.get(name));
	}

	@Override /* ConfigStore */
	public synchronized String write(String name, String expectedContents, String newContents) throws IOException {

		// This is a no-op.
		if (isEquals(expectedContents, newContents))
			return null;

		String currentContents = read(name);

		if (expectedContents != null && ! isEquals(currentContents, expectedContents))
			return currentContents;

		update(name, newContents);

		return null;
	}

	@Override /* ConfigStore */
	public synchronized boolean exists(String name) {
		try {
			return ! read(name).isEmpty();
		} catch (IOException e) {
			return false;
		}
	}

	@Override /* ConfigStore */
	public synchronized ConfigClasspathStore update(String name, String newContents) {
		if (newContents == null)
			cache.remove(name);
		else
			cache.put(name, newContents);
		super.update(name, newContents);
		return this;
	}

	/**
	 * No-op.
	 */
	@Override /* Closeable */
	public void close() throws IOException {
		// No-op
	}

	//-----------------------------------------------------------------------------------------------------------------
	// Other methods.
	//-----------------------------------------------------------------------------------------------------------------

	@Override /* Context */
	public ObjectMap toMap() {
		return super.toMap()
			.append("ConfigClasspathStore", new DefaultFilteringObjectMap()
			);
	}
}