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# JNLP API Examples

This section includes the following topics:

- Introduction
- Using the `BasicService` Service
- Using the `ClipboardService` Service
- Using the `DownloadService` Service
- Using the `DownloadService2` Service
- Implementing the `DownloadServiceListener` Service
- Using the `FileOpenService` Service
- Using the `FileSaveService` Service
- Using the `IntegrationService` Service
- Using the `PrintService` Service
- Using the `PersistenceService` Service
- Using `FileContents`
- Using a `JNLPRandomAccessFile`
- Using the `SingleInstanceService` Service
- Using the `ExtendedService` Service

## Introduction

The JNLP API provides additional information to the application that would otherwise not be available using the standard Java Platform Standard Edition API. For untrusted applications, the JNLP API provides methods for operations such as reading and writing files or accessing the clipboard or printers, which would otherwise be prevented by the security manager.

The public classes and interfaces in the JNLP API are included in the `javaws.jar` file, which is in the JRE's `lib` directory. This JAR file must be included in the class path when compiling source files that use the JNLP API. For example on Windows:

    javac -classpath .;javaws.jar *.java

## Using the `BasicService` Service

The `javax.jnlp.BasicService` service provides a set of methods for querying and interacting with the environment similar to what the `AppletContext` provides for a Java Applet.

The `showURL` method uses the JNLP API to direct the default browser on the platform to show the given URL. The method returns true if the request succeeds, otherwise false.

`import javax.jnlp.*;`
`...`

`// Method to show a URL`
`boolean showURL(URL url) {`
`try {`
`// Lookup the javax.jnlp.BasicService object`
`BasicService bs = (BasicService)ServiceManager.lookup("javax.jnlp.BasicService");`
`// Invoke the showDocument method`
`return bs.showDocument(url);`
`} catch(UnavailableServiceException ue) {`
`// Service is not supported`
`return false;`
`}`
`}`

## Using the `ClipboardService` Service

The `javax.jnlp.ClipboardService` service provides methods for accessing the shared system-wide clipboard, even for applications that are running in the restricted execution environment.

Java Web Start will warn the user of the potential security risk of letting an untrusted application access potentially confidential information stored in the clipboard, or overwriting contents stored in the clipboard.

`import javax.jnlp;`
`...`

`private ClipboardService cs;`

`try {`
`cs = (ClipboardService)ServiceManager.lookup`
`("javax.jnlp.ClipboardService");`
`} catch (UnavailableServiceException e) {`
`cs = null;`
`}`

`if (cs != null) {`
`// set the system clipboard contents to a string selection`
`StringSelection ss = new StringSelection("Java Web Start!");`
`cs.setContents(ss);`
`// get the contents of the system clipboard and print them`
`Transferable tr = cs.getContents();`
`if (tr.isDataFlavorSupported(DataFlavor.stringFlavor)) {`
`try {`
`String s = (String)tr.getTransferData(DataFlavor.stringFlavor);`
`System.out.println("Clipboard contents: " + s);`
`} catch (Exception e) {`
`e.printStackTrace();`
`}`
`}`
`}`

## Using the `DownloadService` Service

The `javax.jnlp.DownloadService` service allows an application to control how its own resources are cached.

The service allows an application to determine which of its resources are cached, to force resources to be cached, and to remove resources from the cache.

    import javax.jnlp.*;
        ...

        DownloadService ds;

        try {
            ds = (DownloadService)ServiceManager.lookup("javax.jnlp.DownloadService");
        } catch (UnavailableServiceException e) {
            ds = null;
        }

        if (ds != null) {

            try {
                // determine if a particular resource is cached
                URL url =
                        new URL("http://www.example.com/draw.jar");
                boolean cached = ds.isResourceCached(url, "1.0");
                // remove the resource from the cache
                if (cached) {
                    ds.removeResource(url, "1.0");
                }
                // reload the resource into the cache
                DownloadServiceListener dsl = ds.getDefaultProgressWindow();
                ds.loadResource(url, "1.0", dsl);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

## Using the `DownloadService2` Service

The `javax.jnlp.DownloadService2` service, introduced in the Java SE 6 update 18 release, provides the following methods:

- `getCachedResources` – Lists cached resources that match the given version, URL and resource type.
- `getUpdateAvailableResources` – Checks and lists resources for which updates are available. If an application uses the version download protocol, specify a version in the `DownloadService2.ResourceSpec`. If not, specify a null value for version.

An instance of the `DownloadService2.ResourceSpec` class specifies details about the resource to be checked.

    import javax.jnlp.*;
    ...
    DownloadService2 service = (DownloadService2)
                            ServiceManager.lookup("javax.jnlp.DownloadService2");

    // create a new instance of ResourceSpec. In this example:
    // - resource is downloaded from a directory on http://foo.bar.com:8080
    // - version is 2. [0-9]+
    // - resource type is JAR
    ResourceSpec spec = new ResourceSpec("http://foo.bar.com:8080/.*", 2.*, service.JAR)

    // returns all cached resources that match the given ResourceSpec
    ResourceSpec results[] = service.getCachedResources(spec);

    // returns all resources for which an update is available on the
    // server http://foo.bar.com:8080.
    results = service.getUpdateAvailableResources(spec);

## Implementing the `DownloadServiceListener` Service

The `javax.jnlp.DownloadServiceListener` service provides methods to specify a customized loading progress indicator that indicates the progress of an application's download. See the Implementing a Customized Loading Progress Indicator topic for more information.

## Using the `FileOpenService` Service

The `javax.jnlp.FileOpenService` service provides methods for importing files from the local disk, even for applications that are running in the restricted execution environment.

This interface is designed to provide the same kind of of disk access to potentially untrusted Web-deployed applications that a Web developer has when using HTML. HTML forms support the inclusion of files by displaying a file open dialog.

    import javax.jnlp.*;
        ...

        FileOpenService fos;

        try {
            fos = (FileOpenService)ServiceManager.lookup("javax.jnlp.FileOpenService");
        } catch (UnavailableServiceException e) {
            fos = null;
        }

        if (fos != null) {
            try {
                // ask user to select a file through this service
                FileContents fc = fos.openFileDialog(null, null);
                // ask user to select multiple files through this service
                FileContents[] fcs = fos.openMultiFileDialog(null, null);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

## Using the `FileSaveService` Service

The `javax.jnlp.FileSaveService` service provides methods for exporting files to the local disk, even for applications that are running in the restricted execution environment.

This interface is designed to provide the same level of disk access to potentially untrusted Web-deployed applications that a Web browser provides for contents that it is displaying. Most browsers provide a Save As... dialog as part of their user interface.

    import javax.jnlp.*;
        ...

        FileSaveService fss;
        FileOpenService fos;

        try {
            fos = (FileOpenService)ServiceManager.lookup("javax.jnlp.FileOpenService");
            fss = (FileSaveService)ServiceManager.lookup
                                       ("javax.jnlp.FileSaveService");
        } catch (UnavailableServiceException e) {
            fss = null;
            fos = null;
        }

        if (fss != null && fos != null) {
            try {
                // get a file with FileOpenService
                FileContents fc = fos.openFileDialog(null, null);
                // one way to save a file
                FileContents newfc = fss.saveFileDialog(null, null,
                fc.getInputStream(), "newFileName.txt");
                // another way to save a file
                FileContents newfc2 = fss.saveAsFileDialog(null, null, fc);

            } catch (Exception e) {
                e.printStackTrace();
            }
        }

Also see Using `FileContents`.

## Using the `IntegrationService` Service

The `javax.jnlp.IntegrationService` service, introduced in the Java SE 6 update 18 release, provides methods for programmatic management of shortcuts. By using this service, an application can perform the following operations:

- An application can create a desktop shortcut.
- An application can create a menu shortcut.
- An application can query and delete shortcuts.
- An application can create, query, and delete associations of an application with a mime-type or file extensions.

    import javax.jnlp.*;
    ...

    IntegrationService is = null;
    try {
        is = (IntegrationService) ServiceManager.lookup("javax.jnlp.IntegrationService");
    } catch(UnavailableServiceException use){
        ...
    }

    // creates a desktop and system menu shortcut; returns true if the shortcuts
    // were created successfully
    boolean result = is.requestShortcut(true, true, null);

    //removes all shortcuts for application
    result = is.removeShortcuts();

    // checks to see if there are shortcuts for the application
    result = is.hasMenuShortcut() && is.hasDesktopShortcut());

    // associates the application with the specified mime-type and file extensions
    String mime = "x-application/aaa";
    String [] exts = {"aaa", "abc"};
    result = is.requestAssociation(mime, exts);

    // checks if the application is associated with the specified mime-type and file extensions
    result = is.hasAssociation(mime, exts);

    // removes association between the application and the specified mime-type and file extensions
    is.removeAssociation(mime, exts);

## Using the `PrintService` Service

The `javax.jnlp.PrintService` service provides methods for access to printing, even for applications that are running in the restricted execution environment.

Using this service, an application can submit a print job. Java Web Start will then show this request to the user and, if accepted, queue the request to the printer.

In Java Web Start 5.0, you can now directly use the Java Printing APIs, and Java Web Start will pop up a security dialog asking the user to grant `PrintPermission` if the application is running in a sandbox. There is no need to use the JNLP Printing APIs anymore. You can have full access to the Java Printing APIs in any JNLP application.

    import javax.jnlp.*;
        ...

        PrintService ps;

        try {
            ps = (PrintService)ServiceManager.lookup("javax.jnlp.PrintService");
        } catch (UnavailableServiceException e) {
            ps = null;
        }

        if (ps != null) {
            try {

                // get the default PageFormat
                PageFormat pf = ps.getDefaultPage();

                // ask the user to customize the PageFormat
                PageFormat newPf = ps.showPageFormatDialog(pf);

                // print the document with the PageFormat above
                ps.print(new DocToPrint());

            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        // Code to construct the Printable Document
        class DocToPrint implements Printable {
            public int print(Graphics g, PageFormat pageformat, int PageIndex){
                // code to generate what you want to print
            }
        }

## Using the `PersistenceService` Service

The `javax.jnlp.PersistenceService` service provides methods for storing data locally on the client system, even for applications that are running in the restricted execution environment.

The service is designed to be somewhat similar to that which the cookie mechanism provides to HTML-based applications. Cookies allow a small amount of data to be stored locally on the client system. That data can be securely managed by the browser and can only be retrieved by HTML pages which originate from the same URL as the page that stored the data.

    import javax.jnlp.*;
        ...

        PersistenceService ps;
        BasicService bs;

        try {
            ps = (PersistenceService)ServiceManager.lookup("javax.jnlp.PersistenceService");
            bs = (BasicService)ServiceManager.lookup("javax.jnlp.BasicService");
        } catch (UnavailableServiceException e) {
            ps = null;
            bs = null;
        }

        if (ps != null && bs != null) {

            try {
                // find all the muffins for our URL
                URL codebase = bs.getCodeBase();
                String [] muffins = ps.getNames(url);

                // get the attributes (tags) for each of these muffins.
                // update the server's copy of the data if any muffins
                // are dirty
                int [] tags = new int[muffins.length];
                URL [] muffinURLs = new URL[muffins.length];
                for (int i = 0; i < muffins.length; i++) {
                    muffinURLs[i] = new URL(codebase.toString() + muffins[i]);
                    tags[i] = ps.getTag(muffinURLs[i]);
                    // update the server if anything is tagged DIRTY
                    if (tags[i] == PersistenceService.DIRTY) {
                        doUpdateServer(muffinURLs[i]);
                    }
                }

                // read in the contents of a muffin and then delete it
                FileContents fc = ps.get(muffinURLs[0]);
                long maxsize = fc.getMaxLength();
                byte [] buf = new byte[fc.getLength()];
                InputStream is = fc.getInputStream();
                long pos = 0;
                while((pos = is.read(buf, pos, buf.length - pos)) > 0) {
                    // just loop
                }
                is.close();

                ps.delete(muffinURLs[0]);

                // re-create the muffin and repopulate its data
                ps.create(muffinURLs[0], maxsize);
                fc = ps.get(muffinURLs[0]);
                // don't append
                OutputStream os = fc.getOutputStream(false);
                os.write(buf);
                os.close();

            } catch (Exception e) {
                e.printStackTrace();
            }
        }

       void doUpdateServer(URL url) {
            // update the server's copy of the persistent data
            // represented by the given URL
            ...
            ps.setTag(url, PersistenceService.CACHED);
       }

## Using `FileContents`

`javax.jnlp.FileContents` objects encapsulate the name and contents of a file. An object of this class is used by the `FileOpenService,` `FileSaveService` and `PersistenceService`. Here is an example of how an instance of a `FileContents` can be used to read from and write to a file:

    import javax.jnlp.*;
        ...

        FileOpenService fos;

        //Initialize fos (see Using the FileOpenService Service example)
        ...

        if (fos != null) {

            try {

                // get a FileContents object to work with from the
                // FileOpenService
                FileContents fc = fos.openFileDialog(null, null);

                // get the InputStream from the file and read a few bytes
                byte [] buf = new byte[fc.getLength()];
                InputStream is = fc.getInputStream();
                int pos = 0;
                while ((pos = is.read(buf, pos, buf.length - pos)) > 0) {
                    // just loop
                }
                is.close();

                // get the OutputStream and write the file back out
                if (fc.canWrite()) {
                   // don't append
                   OutputStream os = fc.getOutputStream(false);
                   os.write(buf);
                }

            } catch (Exception e) {
                e.printStackTrace();
            }
        }

## Using a `JNLPRandomAccessFile`

Instances of `javax.jnlp.JNLPRandomAccessFile` support both reading and writing to a random access file. A random access file behaves like a large array of bytes stored in the file system. Here is an example of how an instance of a `JNLPRandomAccessFile` can be used to write to a random access file:

    import javax.jnlp.*;
        ...

        FileOpenService fos;

        //Initialize fos (see Using the FileOpenService Service example)
        ...

        if (fos != null) {
            try {
               // ask the user to choose a file to open
               FileContents fc = fos.openFileDialog(null, null);

               // attempt to increase the maximum file length
               long grantedLength = fc.getLength();
               if (grantedLength + 1024 > fc.getMaxLength()) {
                   // attempt to increase the maximum file size defined by
                   // the client
                   grantedLength = fc.setMaxLength(grantedLength + 1024);
               }

               // if we were able to increase the maximum allowable file size,
               // get a JNLPRandomAccessFile representation of the file, and
               // write to it
               if (fc.getMaxSize() > fc.getLength() && fc.canWrite()) {
                   JNLPRandomAccessFile raf = fc.getRandomAccessFile("rw");
                   raf.seek(raf.length() - 1);
                   raf.writeUTF("Java Web Start!");
                   raf.close();
               }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

## Using the `SingleInstanceService` Service

The `javax.jnlp.SingleInstanceService` provides a set of methods for applications to register themselves as singletons, and to register listener(s) for handling arguments passed in from different instances of applications.

    import javax.jnlp.*;
        ...

        SingleInstanceService sis;

        ...

        try {
            sis =
    (SingleInstanceService)ServiceManager.lookup("javax.jnlp.SingleInstanceService");
        } catch (UnavailableServiceException e) { sis=null; }

        ...

        // Register the single instance listener at the start of your application

        SISListener sisL = new SISListener();
        sis.addSingleInstanceListener(sisL);

        ...

        // Remember to remove the listener before your application exits

        sis.removeSingleInstanceListener(sisL);
        System.exit(0);

        // Implement the SingleInstanceListener for your application

        class SISListener implements SingleInstanceListener {
            public void newActivation(String[] params) {

                // your code to handle the new arguments here

                ...
            }
        }

## Using an `ExtendedService` Service

The `javax.jnlp.ExtendedService` provides additional support to the current JNLP API. It allows applications to open specific file(s) in the client's file system.

    import javax.jnlp.*;
        ...

        ExtendedService es;

        ...

        try {
            es =
    (ExtendedService)ServiceManager.lookup("javax.jnlp.ExtendedService");
        } catch (UnavailableServiceException e) { es=null; }

        ...

        // Open a specific file in the local machine

        File a = new File("c:\somefile.txt");

        ...

        // Java Web Start will pop up a dialog asking the user to grant permission
        // to read/write the file c:\somefile.txt

        FileContents fc_a = es.openFile(a);

        // You can now use the FileContents object to read/write the file

        ...

        // Open a specific set of files in the local machine

        File[2] fArray = new File[2];

        fArray[0] = a;
        fArray[1] = new File("c:\anotherFile.txt");

        // Java Web Start will pop up a dialog asking the user to grant permission
        // to read/write files in fArray

        FileContents[] fc_Array = es.OpenFiles(fArray);

        // You can now read/write the set of files in fc_Array using the
        // FileContents objects

        }

For detailed information on using `javaws`, see the `javaws` documentation (Solaris, Linux, and macOS or Windows).

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