Android Open Source - wolPi Android Service Loader

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License

The source code is released under:

Apache License

Java Source Code

package de.matthesrieke.wolpi.util;
//  w  ww .  j a  v a  2  s. com
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

import java.net.URL;

import java.util.ArrayList;
import java.util.Collection;

/**
 * Android variant of the famous java.util.ServiceLoader.
 * Services description files are read by default from
 * {@value #DEFAULT_BASE_LOCATION}. 
 * 
 * @author matthes rieke
 *
 * @param <S> the interface for which implementations are loaded.
 */
public final class AndroidServiceLoader<S> {

  public static final String DEFAULT_BASE_LOCATION = "AndroidServiceLoader/services/";

  private ClassLoader classLoaderInstance;
  private Class<S> theInterface;

  private String baseLocation;

  private Collection<S> cached;

  private AndroidServiceLoader(Class<S> ntrfce, String location,
      ClassLoader loader) {
    theInterface = ntrfce;
    classLoaderInstance = loader;
    baseLocation = location;
  }

  /**
   * @return the loaded interface implementations
   */
  public Collection<S> implementations() {
    if (cached == null) {
      cached = loadImplementations();
    }
    return cached;
  }

  private Collection<S> loadImplementations() {
    Collection<S> result = new ArrayList<S>();

    URL baseUrl = classLoaderInstance.getResource(baseLocation+theInterface.getCanonicalName());

    BufferedReader br = null;
    try {
      br = new BufferedReader(new InputStreamReader(baseUrl.openStream(),
          "UTF-8"));
      while (br.ready()) {
        parseLine(br.readLine(), result);
      }
    } catch (IOException x) {
      throw new RuntimeException(x);
    } finally {
      try {
        if (br != null)
          br.close();
      } catch (IOException y) {
        throw new RuntimeException("Error closing file stream:"
            + baseUrl);
      }
    }

    return result;
  }

  @SuppressWarnings("unchecked")
  private void parseLine(String line, Collection<S> result) {
    if (line == null)
      return;
    
    String tmp = line.trim();
    
    if (tmp.startsWith("#"))
      return;
    
    try {
      Class<?> clazz = Class.forName(tmp);
      if (theInterface.isAssignableFrom(clazz)) {
        result.add((S) clazz.newInstance());
      }
    } catch (ClassNotFoundException e) {
      return;
    } catch (InstantiationException e) {
      return;
    } catch (IllegalAccessException e) {
      return;
    }
    
  }

  /**
   * Services description files are read by default from
   * {@value #DEFAULT_BASE_LOCATION}. 
   * 
   * @param service the interface
   * @return the object providing access to the implementations
   */
  public static <S> AndroidServiceLoader<S> load(Class<S> service) {
    return load(service, DEFAULT_BASE_LOCATION);
  }

  /**
   * Services description files are read from
   * baseLocation parameter. 
   * 
   * @param service the interface
   * @param baseLocation the directory for service description files
   * @return the object providing access to the implementations
   */
  public static <S> AndroidServiceLoader<S> load(Class<S> service,
      String baseLocation) {
    ClassLoader cl = Thread.currentThread().getContextClassLoader();
    return load(service, baseLocation, cl);
  }

  /**
   * Services description files are read from
   * baseLocation parameter by the defined loader.
   * 
   * @param service the interface
   * @param baseLocation the directory for service description files
   * @param loader ClassLoader to use
   * @return the object providing access to the implementations
   */
  public static <S> AndroidServiceLoader<S> load(Class<S> service,
      String baseLocation, ClassLoader loader) {
    return new AndroidServiceLoader<S>(service, baseLocation, loader);
  }
  
}

Java Source Code List

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