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Converting a resource into a byte array in Java ME

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ID   Creation date May 21, 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, follow these instructions:

  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 from which the resource can be found (e.g. 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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