io.dropwizard.bundles.webjars.VersionLoader Maven / Gradle / Ivy

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Dropwizard bundle to make working with Webjars (http://webjars.org) easier.

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package io.dropwizard.bundles.webjars;

import com.google.common.cache.CacheLoader;
import com.google.common.io.Closer;
import com.google.common.io.Resources;

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.Properties;

/**
 * Determines the version of the webjar that's in the classpath for a particular library.
 * 
 * The version of a webjar can be determined by looking at the pom.properties file
 * located at {@code META-INF/maven///pom.properties}.
 * 
 * Where {@code } is the name of the maven group the webjar artifact is part of, and
 * {@code } is the name of the library.
 */
class VersionLoader extends CacheLoader {
  public static final String NOT_FOUND = "VERSION-NOT-FOUND";

  private final Iterable groups;

  VersionLoader(Iterable groups) {
    this.groups = groups;
  }

  @Override
  public String load(String library) throws Exception {
    for (String group : groups) {
      String found = tryToLoadFrom("META-INF/maven/%s/%s/pom.properties", group, library);
      if (found != null) {
        return found;
      }
    }

    return NOT_FOUND;
  }

  private String tryToLoadFrom(String format, String group, String library) {
    String path = String.format(format, group, library);
    URL url;
    try {
      url = Resources.getResource(path);
    } catch (IllegalArgumentException e) {
      return null;
    }

    try {
      Closer closer = Closer.create();
      InputStream in = closer.register(url.openStream());
      try {
        Properties props = new Properties();
        props.load(in);

        return props.getProperty("version");
      } finally {
        closer.close();
      }
    } catch (IOException e) {
      return null;
    }
  }
}