dataflavor.java

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/* DataFlavor.java -- A type of data to transfer via the clipboard.
   Copyright (C) 1999, 2001, 2004, 2005 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Classpath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version. */


package java.awt.datatransfer;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import java.io.Reader;
import java.io.StringReader;
import java.io.UnsupportedEncodingException;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.rmi.Remote;

/**
 * This class represents a particular data format used for transferring
 * data via the clipboard.
 *
 * @author Aaron M. Renn ([e-mail])
 */
public class DataFlavor implements java.io.Externalizable, Cloneable
{
  static final long serialVersionUID = 8367026044764648243L;

  // FIXME: Serialization: Need to write methods for.

  /**
   * This is the data flavor used for tranferring plain text.  The MIME
   * type is "text/plain; charset=unicode".  The representation class
   * is <code>java.io.InputStream</code>.
   *
   * @deprecated The charset unicode is platform specific and InputStream
   * deals with bytes not chars. Use <code>getRederForText()</code>.
   */
  public static final DataFlavor plainTextFlavor = 
    new DataFlavor(java.io.InputStream.class,
                   "text/plain; charset=unicode",
                   "plain unicode text");

  /**
   * This is the data flavor used for transferring Java strings.  The
   * MIME type is "application/x-java-serialized-object" and the 
   * representation class is <code>java.lang.String</code>.
   */
  public static final DataFlavor stringFlavor = 
    new DataFlavor(java.lang.String.class, "Java Unicode String");

  /**
   * This is a data flavor used for transferring lists of files.  The
   * representation type is a <code>java.util.List</code>, with each 
   * element of the list being a <code>java.io.File</code>.
   */
  public static final DataFlavor javaFileListFlavor = 
    new DataFlavor(java.util.List.class,
                   "application/x-java-file-list; class=java.util.List",
                   "Java File List");

  /**
   * This is an image flavor used for transferring images.  The
   * representation type is a <code>java.awt.Image</code>.
   */
  public static final DataFlavor imageFlavor = 
    new DataFlavor(java.awt.Image.class, "Java Image");

  /**
   * This is the MIME type used for transferring a serialized object.
   * The representation class is the type of object be deserialized.
   */
  public static final String javaSerializedObjectMimeType =
    "application/x-java-serialized-object";

  /**
   * This is the MIME type used to transfer a Java object reference within
   * the same JVM.  The representation class is the class of the object
   * being transferred.
   */
  public static final String javaJVMLocalObjectMimeType =
    "application/x-java-jvm-local-objectref";

  /**
   * This is the MIME type used to transfer a link to a remote object.
   * The representation class is the type of object being linked to.
   */
  public static final String javaRemoteObjectMimeType =
    "application/x-java-remote-object";

  /*
   * Instance Variables
   */
  
  // The MIME type for this flavor
  private final String mimeType;
  
  // The representation class for this flavor
  private final Class representationClass;
  
  // The human readable name of this flavor
  private String humanPresentableName;

  /*
   * Static Methods
   */
  
  /**
   * This method attempts to load the named class.  The following class
   * loaders are searched in order: the bootstrap class loader, the
   * system class loader, the context class loader (if it exists), and
   * the specified fallback class loader.
   *
   * @param className The name of the class to load.
   * @param classLoader The class loader to use if all others fail, which
   * may be <code>null</code>.
   *
   * @exception ClassNotFoundException If the class cannot be loaded.
   */
  protected static final Class tryToLoadClass(String className,
                                             ClassLoader classLoader)
    throws ClassNotFoundException
  {
    // Bootstrap
    try
      {
        return Class.forName(className);
      }
    catch(ClassNotFoundException cnfe)
      {
	// Ignored.
      }
  
    // System
    try
      {
	ClassLoader loader = ClassLoader.getSystemClassLoader();
        return Class.forName(className, true, loader);
      }
    catch(ClassNotFoundException cnfe)
      {
	// Ignored.
      }
 
    // Context
    try
      {
	ClassLoader loader = Thread.currentThread().getContextClassLoader();
        return Class.forName(className, true, loader);
      }
    catch(ClassNotFoundException cnfe)
      {
	// Ignored.
      }
 
    if (classLoader != null)
      return Class.forName(className, true, classLoader);

    throw new ClassNotFoundException(className);
  }
  
  private static Class getRepresentationClassFromMime(String mimeString,
                                                      ClassLoader classLoader)
    {
      String classname = getParameter("class", mimeString);
      if (classname != null)
        {
          try
            {
              return tryToLoadClass(classname, classLoader);
            }
          catch(Exception e)
            {
	      IllegalArgumentException iae;
              iae = new IllegalArgumentException("mimeString: "
						 + mimeString
			      			 + " classLoader: "
						 + classLoader);
	      iae.initCause(e);
	      throw iae;
            }
        }
      else
        return java.io.InputStream.class;
    }
  
  /**
   * Returns the value of the named MIME type parameter, or <code>null</code>
   * if the parameter does not exist. Given the parameter name and the mime
   * string.
   *
   * @param paramName The name of the parameter.
   * @param mimeString The mime string from where the name should be found.
   *
   * @return The value of the parameter or null.
   */
  private static String getParameter(String paramName, String mimeString)
  {
    int idx = mimeString.indexOf(paramName + "=");
    if (idx == -1)
      return(null);
  
    String value = mimeString.substring(idx + paramName.length() + 1);
  
    idx = value.indexOf(" ");
    if (idx == -1)
      return(value);
    else
      return(value.substring(0, idx));
  }
  
  /**
   * XXX - Currently returns <code>plainTextFlavor</code>.
   */
  public static final DataFlavor getTextPlainUnicodeFlavor()
  {
    return plainTextFlavor;
  }
  
  /**
   * Selects the best supported text flavor on this implementation.
   * Returns <code>null</code> when none of the given flavors is liked.
   *
   * The <code>DataFlavor</code> returned the first data flavor in the
   * array that has either a representation class which is (a subclass of)
   * <code>Reader</code> or <code>String</code>, or has a representation
   * class which is (a subclass of) <code>InputStream</code> and has a
   * primary MIME type of "text" and has an supported encoding.
   */
  public static final DataFlavor 
    selectBestTextFlavor(DataFlavor[] availableFlavors)
  {
    for(int i = 0; i < availableFlavors.length; i++)
      {
        DataFlavor df = availableFlavors[i];
        Class c = df.representationClass;
  
        // A Reader or String is good.
        if ((Reader.class.isAssignableFrom(c))
           || (String.class.isAssignableFrom(c)))
      return df;
  
        // A InputStream is good if the mime primary type is "text"
        if ((InputStream.class.isAssignableFrom(c))
           && ("text".equals(df.getPrimaryType())))
          {
            String encoding = availableFlavors[i].getParameter("charset");
            if (encoding == null)
              encoding = "us-ascii";
            Reader r = null;
            try
              {
                // Try to construct a dummy reader with the found encoding
                r = new InputStreamReader
                      (new ByteArrayInputStream(new byte[0]), encoding);
              }
            catch(UnsupportedEncodingException uee) { /* ignore */ }

            if (r != null)
              return df;
          }
      }
  
    // Nothing found
    return null;
  }


  /*
   * Constructors
   */
  
  /**
   * Empty public constructor needed for externalization.
   * Should not be used for normal instantiation.
   */
  public DataFlavor()
  {
    mimeType = null;
    representationClass = null;
    humanPresentableName = null;
  }

  /**
   * Private constructor.
   */
  private DataFlavor(Class representationClass,
                    String mimeType,
                    String humanPresentableName)
  {
    this.representationClass = representationClass;
    this.mimeType = mimeType;
    if (humanPresentableName != null)
      this.humanPresentableName = humanPresentableName;
    else
      this.humanPresentableName = mimeType;
  }

  /**
   * Initializes a new instance of <code>DataFlavor</code>.  The class
   * and human readable name are specified, the MIME type will be
   * "application/x-java-serialized-object". If the human readable name
   * is not specified (<code>null</code>) then the human readable name
   * will be the same as the MIME type.
   *
   * @param representationClass The representation class for this object.
   * @param humanPresentableName The display name of the object.
   */
  public DataFlavor(Class representationClass, String humanPresentableName)
  {
    this(representationClass,
         "application/x-java-serialized-object"
         + "; class="
         + representationClass.getName(),
         humanPresentableName);
  }

  /**
   * Initializes a new instance of <code>DataFlavor</code> with the
   * specified MIME type and description.  If the MIME type has a
   * "class=&lt;rep class&gt;" parameter then the representation class will
   * be the class name specified. Otherwise the class defaults to
   * <code>java.io.InputStream</code>. If the human readable name
   * is not specified (<code>null</code>) then the human readable name
   * will be the same as the MIME type.
   *
   * @param mimeType The MIME type for this flavor.
   * @param humanPresentableName The display name of this flavor.
   * @param classLoader The class loader for finding classes if the default
   * class loaders do not work.
   *
   * @exception IllegalArgumentException If the representation class
   * specified cannot be loaded.
   * @exception ClassNotFoundException If the class is not loaded.
   */
  public DataFlavor(String mimeType, String humanPresentableName, 
                   ClassLoader classLoader)
    throws ClassNotFoundException
  {
    this(getRepresentationClassFromMime(mimeType, classLoader),
         mimeType, humanPresentableName);
  }

  /**
   * Initializes a new instance of <code>DataFlavor</code> with the
   * specified MIME type and description.  If the MIME type has a
   * "class=&lt;rep class&gt;" parameter then the representation class will
   * be the class name specified. Otherwise the class defaults to
   * <code>java.io.InputStream</code>. If the human readable name
   * is not specified (<code>null</code>) then the human readable name
   * will be the same as the MIME type. This is the same as calling
   * <code>new DataFlavor(mimeType, humanPresentableName, null)</code>.
   *
   * @param mimeType The MIME type for this flavor.
   * @param humanPresentableName The display name of this flavor.
   *
   * @exception IllegalArgumentException If the representation class
   * specified cannot be loaded.
   */
  public DataFlavor(String mimeType, String humanPresentableName)
  {
    this(getRepresentationClassFromMime (mimeType, null),
        mimeType, humanPresentableName);
  }

  /**
   * Initializes a new instance of <code>DataFlavor</code> with the specified
   * MIME type.  This type can have a "class=" parameter to specify the
   * representation class, and then the class must exist or an exception will
   * be thrown. If there is no "class=" parameter then the representation class
   * will be <code>java.io.InputStream</code>. This is the same as calling
   * <code>new DataFlavor(mimeType, null)</code>.
   *
   * @param mimeType The MIME type for this flavor.
   *
   * @exception IllegalArgumentException If a class is not specified in
   * the MIME type.
   * @exception ClassNotFoundException If the class cannot be loaded.
   */
  public DataFlavor(String mimeType) throws ClassNotFoundException
  {
    this(mimeType, null);
  }

  /**
   * Returns the MIME type of this flavor.
   *
   * @return The MIME type for this flavor.
   */
  public String getMimeType()
  {
    return(mimeType);
  }

  /**
   * Returns the representation class for this flavor.
   *
   * @return The representation class for this flavor.
   */
  public Class getRepresentationClass()
  {
    return(representationClass);
  }

  /**
   * Returns the human presentable name for this flavor.
   *
   * @return The human presentable name for this flavor.
   */
  public String getHumanPresentableName()
  {
    return(humanPresentableName);
  } 

  /**
   * Returns the primary MIME type for this flavor.
   *
   * @return The primary MIME type for this flavor.
   */
  public String getPrimaryType()
  {
    int idx = mimeType.indexOf("/");
    if (idx == -1)
      return(mimeType);
  
    return(mimeType.substring(0, idx));
  }

  /**
   * Returns the MIME subtype for this flavor.
   *
   * @return The MIME subtype for this flavor.
   */
  public String getSubType()
  {
    int start = mimeType.indexOf("/");
    if (start == -1)
      return "";
  
    int end = mimeType.indexOf(";", start + 1);
    if (end == -1)
      return mimeType.substring(start + 1);
    else
      return mimeType.substring(start + 1, end);
  }

  /**
   * Returns the value of the named MIME type parameter, or <code>null</code>
   * if the parameter does not exist.
   *
   * @param paramName The name of the paramter.
   *
   * @return The value of the parameter.
   */
  public String getParameter(String paramName)