Java Network Launch Protocol (JNLP) - Managing Java Applications Resources, Slides of Java Programming

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Java Network Launch Protocol (JNLP)

What it is

• A clever way to manage the contents of your java applications

on a client’s computer.

• If you have an complicated application requiring resources to

be downloaded to a client’s machine, this technology

manages those resources.

• This technology ensures all users of your java applications

always have the most up to date files to work from.

• This is done with almost no effort on the user’s end.

More Details

• When a regular application is launched, the location of resources

must already be known

• This is tough to do with a distributed application since a developer

would need to specify all file paths on a user’s computer as well as

web resources.

• But there is a better way: A launcher Program
• This “launcher” program collects local and web resources needed by

the application and lets the JVM know where everything is.

• This way, when the application starts, all the resources are already

available.

Pictorial Representation

Client Computer JNLP Client URL JNLP Server With resource files Web Resources JVM Resources Java Application Native Rsources

Advantages

• A rich client environment at runtime. Developers can use a new

API to access system resources.

• A secure deployment solution. End users can trust a reliable

JNLP Client and let that client manage additional files required

by the application.

• Applications can evolve through incremental updates.

• Multiple JREs management and automatic installation of

additional JREs and optional packages.

More Advantages

• Offline operation. Deployed applications can work even

without a connection with the deployment server.

• Automatic installation of native code/libraries. Some Java

programs may need some platform-specific support for

running.

• JNLP Client management console.

• The capability of using platform-dependent facilities such as

shortcuts, accelerators, and utilities.

An Example

• In this example we will setup the environment

for using .jnlp files

• Go through the creation of the files needed to

execute program with JNLP.

• Deploy the application locally

• Deploy the application on NJITs AFS server

running Apache Tomcat

The Application

• This example connects to United States National Institute of

Standards and Technology and retrieves the current time

• It is a JFrame, not an applet, since it doesn’t extend applet and

therefore can be compiled and executed from the command line

• Is not embedded in an html file

Code Part 2

Container content = frame.getContentPane(); content.add(label, BorderLayout.CENTER); String message = "missing"; BufferedReader reader = null; try { Socket socket = new Socket("time.nist.gov", 13); InputStream is = socket.getInputStream(); InputStreamReader isr = new InputStreamReader(is); reader = new BufferedReader(isr); reader.readLine(); // skip blank line message = reader.readLine(); } catch (MalformedURLException e) { System.err.println("Malformed: " + e); } catch (IOException e) { System.err.println("I/O Exception: " + e);

Code Part 3

} finally { if (reader != null) { try { reader.close(); } catch (IOException ignored) { } } } label.setText(message); frame.pack(); frame.show(); } }

.jnlp Code Part 1

NJIT - CS633 JNLP Demo

.jnlp Code Part 2

<application-desc main-class="TheTime" />

• The Codebase is the location of the .jar file we will create for

this application

• The Information section contains the information the splash

screen will display

More on the .jnlp file

• We specify the main class as TheTime in the

Application tag. This is the name of our

compiled class. We would not need to do this

if we specified one class in the jar file as the

main class. This would be done if we used

multiple jar files.

Create the JAR file

• First create the JAR file

jar cf JNLPTime.jar TheTime.class

• Create a key in the keystore

keytool -genkey -keystore myKeys -alias jdc

• Sign the JAR file

jarsigner -keystore myKeys JNLPTime.jar jdc