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Revision as of 10:02, 27 May 2008 by Forum Nokia KB (Talk | contribs)

Converting a resource into a byte array in Java ME

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Template:KBCS

ID CS000979 Creation date May 27, 2008
Platform S60 3rd Edition, FP1 Tested on devices Nokia N95 8GB
Category Java ME Subcategory WMA 2.0 (JSR-205)


Keywords (APIs, classes, methods, functions): java.lang.Class, java.io.InputStream, java.io.ByteArrayOutputStream, java.io.IOException, java.lang.Class.getResourceAsStream(), java.io.InputStream.read(), java.io.ByteArrayOutputStream.write(), java.io.ByteArrayOutputStream.toByteArray(), java.io.InputStream.close(), java.io.ByteArrayOutputStream.close()

Overview

This code snippet demonstrates how to convert a resource into a byte array. The snippet assumes that the resource is included in the JAR file, which is used to distribute the application.

Example: To include a file to the JAR package in NetBeans 6.1, do as follows:

  1. In the Projects window (select Window > Projects if it's not visible), open the project node for the project to which you want to add the file.
  2. Right-click on the Resources node under the project and choose Add Folder. The Add Folder dialog box opens.
  3. Select the folder where the resource is (for example, dist/images).
  4. Click Open. The folder is added to the project.
  5. Clean and build the project (right-click on the project node and select Clean & Build).
  6. The resource can be obtained in the code, for example, like this:
InputStream inputStream = getClass().getResourceAsStream("image.jpg");
// ...

Source

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
/**
* Constructs a byte array and fills it with data that is read from the
* specified resource.
* @param filename the path to the resource
* @return the specified resource as a byte array
* @throws java.io.IOException if the resource cannot be read, or the
* bytes cannot be written, or the streams cannot be closed
*/

private byte[] obtainByteData(String filename) throws IOException {
InputStream inputStream = getClass().getResourceAsStream(filename);
ByteArrayOutputStream outputStream = new ByteArrayOutputStream(1024);
byte[] bytes = new byte[512];
 
// Read bytes from the input stream in bytes.length-sized chunks and write
// them into the output stream
int readBytes;
while ((readBytes = inputStream.read(bytes)) > 0) {
outputStream.write(bytes, 0, readBytes);
}
 
// Convert the contents of the output stream into a byte array
byte[] byteData = outputStream.toByteArray();
 
// Close the streams
inputStream.close();
outputStream.close();
 
return byteData;
}

The method above can be used, for example, with multipart messages. In the following, a MessagePart object is constructed from a byte array which represents raw data from a JPEG image:

import javax.wireless.messaging.MessagePart;
import javax.wireless.messaging.SizeExceededException;
 
// ...
 
/**
* Constructs a MessagePart which can be added to a MultipartMessage.
* @return the constructed MessagePart
* @throws javax.wireless.messaging.SizeExceededException if the contents
* is larger than the available memory or supported size for the message
* part
* @throws java.io.IOException if the byte data cannot be obtained
*/

private MessagePart createMsgPart() throws SizeExceededException,
IOException {
String imageContentID = "image01";
String imageContentLocation = "image.jpg";
String jpgMIME = "image/jpeg";
// Convert the image into a byte array and construct a message part using
// it
byte[] imageContent = obtainByteData(imageContentLocation);
MessagePart messagePart = new MessagePart(imageContent, jpgMIME,
imageContentID, imageContentLocation, null);
return messagePart;
}

Postconditions

A specified resource is converted into a byte array.

See also

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