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Trail: Deployment
Lesson: Java Web Start

Answers to Questions and Exercises: Java Web Start

Questions

  1. Question: In a link that is to run a Java Web Start application, which file is specified as the a tag's href attribute?

    Answer: You use the application's JNLP file name as the value of the href attribute. When a user clicks the link to the JNLP file, Java Web Start loads the application specified by that JNLP file.

  2. Question: Which MIME type must a Web server recognize in order for it to host Java Web Start applications?

    Answer: You must configure the Web server so that files with the .jnlp extension are set to the application/x-java-jnlp-file MIME type.

  3. Question: In an application's JNLP file, which two elements must be specified within the resources element?

    Answer: The resources element must contain:

    • The j2se element, which specifies the Java platform on which to run the application.
    • The jar element, which specifies the JAR file for the application.
  4. Question: Which interface provides the ability to control how the Java Web Start application's resources are cached?

    1. BasicService
    2. DownloadService
    3. PersistenceService
    4. ExtendedService

    Answer: B. The DownloadService interface provides the ability to control how the application's resources are cached.

  5. Question: True or False: Java Web Start applications run in a secure sandbox by default.

    Answer: True.

  6. Question: True or False: If a Java Web Start application is running in a secure sandbox, JAR files for the application can reside on different servers.

    Answer: False. All JAR files for the application must reside on the same server.

  7. Question: For a Java Web Start application to support operations outside of the secure sandbox, what must you do with its JAR files?

    Answer: You must sign JAR files to enable your application can work outside of the sandbox.

Exercises

  1. Exercise: Write the XML code you would add to a JNLP file in order to request that the application have complete access to the client system.

    Answer:

    <security>
       <all-permissions/>
    </security> 
    
  2. Exercise: For a Java Web Start application, you have two icons, one.gif and two.gif, in the images directory in a JAR file. Write the application code you would use to access these images.

    Answer:

    // Get current classloader
    ClassLoader cl = this.getClass().getClassLoader();
    // Create icons
    Icon firstIcon  = new ImageIcon(cl.getResource("images/one.gif"));
    Icon secondIcon   = new ImageIcon(cl.getResource("images/two.gif"));
    

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