Manifest Writer : JarFile « File « Java Tutorial

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import java.util.jar.Manifest;
import java.util.jar.Attributes;
import java.util.LinkedList;
import java.util.List;
import java.util.Iterator;
import java.io.*;

/** Writes manifest objects.  Useful for creating Manifest files without writing them to files. */
public class ManifestWriter {
  private List<String> _classPaths;
  private String _mainClass;
  private String _rawManifest;
  public static final Manifest DEFAULT = new ManifestWriter().getManifest();
  
  /** Create a new manifest file */
  public ManifestWriter() {
    _classPaths = new LinkedList<String>();
    _mainClass = null;
    _rawManifest = null;
  }
  
  /** Add a class path to the Manifest
    * @param path the path to be added
    */
  public void addClassPath(String path) {
    _classPaths.add(_classPaths.size(), path);
  }
  
  /** Set the main class of the Manifest
    * @param mainClass
    */
  public void setMainClass(String mainClass) {
    _mainClass = mainClass;
    _rawManifest = null;
  }
  
  public void setManifestContents(String rawManifest) {
    _rawManifest =  rawManifest;
    _mainClass = null;
  }
  
  /** Get an input stream to the contents of the manifest file
    * @return an InputStream whose contents are the contents of the Manifest file
    */
  protected InputStream getInputStream() {
    // NOTE: All significant lines in the manifest MUST end in the end of line character
    
    final StringBuilder sbuf = new StringBuilder();
    sbuf.append(Attributes.Name.MANIFEST_VERSION.toString());
    sbuf.append(": 1.0" + "\n");
    if( !_classPaths.isEmpty() ) {
      Iterator<String> iter = _classPaths.iterator();
      sbuf.append(Attributes.Name.CLASS_PATH.toString());
      sbuf.append(":");
      while (iter.hasNext()) {
        sbuf.append(" ");
        sbuf.append(iter.next());
      }
      sbuf.append("\n");
    }
    if( _mainClass != null ) {
      sbuf.append(Attributes.Name.MAIN_CLASS.toString());
      sbuf.append(": ");
      sbuf.append(_mainClass);
      sbuf.append("\n");
    }
    
    if(_rawManifest != null) {
      sbuf.append(_rawManifest); 
      
      if(!_rawManifest.endsWith("\n"))
        sbuf.append("\n");
    }
    
    try { return new ByteArrayInputStream(sbuf.toString().getBytes("UTF-8")); }
    catch (UnsupportedEncodingException e) { throw new RuntimeException(e); }
  }
  
  /** Get the Manifest object that this object created.
    * @return the Manifest that this builder created
    */
  public Manifest getManifest() {
    try {
      Manifest m = new Manifest();
      m.read(getInputStream());
      return m;
    }
    catch (IOException e) {
      e.printStackTrace();
      return null;
    }
  }
}