MainAttributes.java

/*
 * This file is part of Mixin, licensed under the MIT License (MIT).
 *
 * Copyright (c) SpongePowered <https://www.spongepowered.org>
 * Copyright (c) contributors
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package org.spongepowered.asm.launch.platform;

import java.io.File;
import java.io.IOException;
import java.net.URI;
import java.util.HashMap;
import java.util.Map;
import java.util.jar.Attributes;
import java.util.jar.JarFile;
import java.util.jar.Manifest;

/**
 * "Main" attribute cache for a URI container, mainly to avoid constantly
 * opening jar files just to read odd values out of the manifest.
 */
final class MainAttributes {
    
    private static final Map<URI, MainAttributes> instances = new HashMap<URI, MainAttributes>();
    
    /**
     * Manifest from jar
     */
    protected final Attributes attributes;
    
    private MainAttributes() {
        this.attributes = new Attributes();
    }

    private MainAttributes(File jar) {
        this.attributes = MainAttributes.getAttributes(jar);
    }

    public final String get(String name) {
        if (this.attributes != null) {
            return this.attributes.getValue(name);
        }
        return null;
    }
    
    private static Attributes getAttributes(File jar) {
        if (jar == null) {
            return null;
        }
        
        JarFile jarFile = null;
        try {
            jarFile = new JarFile(jar);
            Manifest manifest = jarFile.getManifest();
            if (manifest != null) {
                return manifest.getMainAttributes();
            }
        } catch (IOException ex) {
            // be quiet checkstyle
        } finally {
            if (jarFile != null) {
                try {
                    jarFile.close();
                } catch (IOException ex) {
                    // this could be an issue later on :(
                }
            }
        }
        return new Attributes();
    }
    
    public static MainAttributes of(File jar) {
        return MainAttributes.of(jar.toURI());
    }

    public static MainAttributes of(URI uri) {
        MainAttributes attributes = MainAttributes.instances.get(uri);
        if (attributes == null) {
            attributes = new MainAttributes(new File(uri));
            MainAttributes.instances.put(uri, attributes);
        }
        return attributes;
    }
}