How to Integrate with the Desktop Class如何与桌面类集成

The Desktop API uses the host operating system's file associations to launch applications associated with specific file types. 桌面API使用主机操作系统的文件关联来启动与特定文件类型关联的应用程序。For example, if OpenDocument text (.odt) file extensions are associated with the OpenOffice Writer application, a Java application could launch OpenOffice Writer to open, edit, or even print files with that association. 例如，如果OpenDocument文本（.odt）文件扩展名与OpenOffice Writer应用程序相关联，Java应用程序可以启动OpenOffice Wliter以打开、编辑甚至打印具有该关联的文件。Depending on the host system, different applications may be associated with different actions. 根据主机系统的不同，不同的应用程序可能与不同的操作相关联。For example, if a particular file cannot be printed, check first whether its extension has a printing association on the given operating system.例如，如果无法打印特定文件，请首先检查其扩展名在给定操作系统上是否具有打印关联。

1. Compile and run the example, consult the example index.编译并运行示例，查阅示例索引。
2. The DesktopDemo dialog box will appear. 将出现DesktopDemo对话框。
3. Enter an URI value into the URI text field, for example – 在URI文本字段中输入URI值，例如&ndash；https://docs.oracle.com/javase/tutorial.
4. Press the Launch Browser button.按Launch Browser（启动浏览器）按钮。
5. Ensure that the default browser window opens and the Tutorial main page is loaded.确保打开默认浏览器窗口并加载教程主页。
6. Change URI to an arbitrary value, press the Launch Browser button, and ensure that the web page you requested is loaded successfully.将URI更改为任意值，按Launch Browser按钮，并确保成功加载您请求的网页。
7. Switch back to the DesktopDemo dialog box and enter a mail recipient name in the E-mail text field. 切换回DesktopDemo对话框，并在电子邮件文本字段中输入邮件收件人姓名。You can also use the mailto scheme supporting CC, BCC, SUBJECT, and BODY fields, for example – duke@example.com?SUBJECT=Hello Duke!.您还可以使用支持CC、BCC、SUBJECT和BODY字段的mailto方案，例如duke@example.com?SUBJECT=Hello Duke!。
8. Press the Launch Mail button.按“启动邮件”按钮。
9. The compositing dialog box of the default email client will appear. 将显示默认Electron邮件客户端的合成对话框。Be sure that the To and Subject fields are as follows. 确保“收件人”和“主题”字段如下所示。
10. You can continue to compose a message or try to enter different combinations of the mail schema in the E-mail field.您可以继续撰写邮件，也可以尝试在“Electron邮件”字段中输入邮件模式的不同组合。
11. Switch back to the DesktopDemo dialog box and press the ellipsis button to choose any text file.切换回DesktopDemo对话框，然后按省略号按钮选择任何文本文件。
12. Select either Open, Edit, or Print to set the type of operation, then press the Launch Application button.选择打开、编辑或打印以设置操作类型，然后按启动应用程序按钮。
13. Be sure that operation completes correctly. 确保操作正确完成。Try other file formats, for example .odt, .html, .pdf. 尝试其他文件格式，例如.odt、.html、.pdf。Note: If you try to edit .pdf file, the DesktopDemo returns the following message: 注意：如果您尝试编辑.pdf文件，DesktopDemo会返回以下消息：Cannot perform the given operation to the <file name> file

The following code snippets provide more details on the DeskDemo application implementation. 以下代码片段提供了有关DeskDemo应用程序实现的更多详细信息。The DesktopDemo constructor disables the few components right after instantiating the UI and checks whether the Desktop API is available.DesktopDemo构造函数在实例化UI后立即禁用少数组件，并检查Desktop API是否可用。

public DesktopDemo() {
        // init all GUI components
        initComponents();
        // disable buttons that launch browser, email client,
        // disable buttons that open, edit, print files
        disableActions();
        // before any Desktop APIs are used, first check whether the API is
        // supported by this particular VM on this particular host
        if (Desktop.isDesktopSupported()) {
            desktop = Desktop.getDesktop();
            // now enable buttons for actions that are supported.
            enableSupportedActions();
        }
        ...

    /**
     * Disable all graphical components until we know
     * whether their functionality is supported.
     */
    private void disableActions() {
        txtBrowserURI.setEnabled(false);
        btnLaunchBrowser.setEnabled(false);
        
        txtMailTo.setEnabled(false);
        btnLaunchEmail.setEnabled(false);
        
        rbEdit.setEnabled(false);
        rbOpen.setEnabled(false);
        rbPrint.setEnabled(false);

        txtFile.setEnabled(false);
        btnLaunchApplication.setEnabled(false);        
    }
    

   ...

Once a Desktop object is acquired, you can query the object to find out which specific actions are supported. 获取Desktop对象后，可以查询该对象以了解支持哪些特定操作。If the Desktop object does not support specific actions, or if the Desktop API itself is unsupported, DesktopDemo simply keeps the affected graphical components disabled.如果桌面对象不支持特定操作，或者桌面API本身不受支持，DesktopDemo只会将受影响的图形组件保持为禁用状态。

/**
     * Enable actions that are supported on this host.
     * The actions are the following: open browser, 
     * open email client, and open, edit, and print
     * files using their associated application.
     */
    private void enableSupportedActions() {
        if (desktop.isSupported(Desktop.Action.BROWSE)) {
            txtBrowserURI.setEnabled(true);
            btnLaunchBrowser.setEnabled(true);
        }
        
        if (desktop.isSupported(Desktop.Action.MAIL)) {
            txtMailTo.setEnabled(true);
            btnLaunchEmail.setEnabled(true);
        }

        if (desktop.isSupported(Desktop.Action.OPEN)) {
            rbOpen.setEnabled(true);
        }
        if (desktop.isSupported(Desktop.Action.EDIT)) {
            rbEdit.setEnabled(true);
        }
        if (desktop.isSupported(Desktop.Action.PRINT)) {
            rbPrint.setEnabled(true);
        }
        
        if (rbEdit.isEnabled() || rbOpen.isEnabled() || rbPrint.isEnabled()) {
            txtFile.setEnabled(true);
            btnLaunchApplication.setEnabled(true);
        }
    }

The browse(uri) method can throw a variety of exceptions, including a NullPointerException if the URI is null, and an UnsupportedOperationException if the BROWSE action is unsupported. browse(uri)方法可以引发各种异常，包括uri为null时的NullPointerException，以及不支持browse操作时的UnsupportedOperationException。This method can throw an IOException if the default browser or application cannot be found or launched, and a SecurityException if a security manager denies the invocation.如果无法找到或启动默认浏览器或应用程序，此方法会引发IOException，如果安全管理器拒绝调用，则会引发SecurityException。

private void onLaunchBrowser(ActionEvent evt) {
        URI uri = null;
        try {
            uri = new URI(txtBrowserURI.getText());
            desktop.browse(uri);
        } catch(IOException ioe) {
            System.out.println("The system cannot find the " + uri + 
                " file specified");
            //ioe.printStackTrace();
        } catch(URISyntaxException use) {
            System.out.println("Illegal character in path");
            //use.printStackTrace();
        }
    }

Applications can launch the host's default email client, if that action is supported, by calling the mail(uriMailTo) method of this Desktop instance.如果支持该操作，应用程序可以通过调用此桌面实例的mail(uriMailTo)方法来启动主机的默认电子邮件客户端。

private void onLaunchMail(ActionEvent evt) {
        String mailTo = txtMailTo.getText();
        URI uriMailTo = null;
        try {
            if (mailTo.length() > 0) {
                uriMailTo = new URI("mailto", mailTo, null);
                desktop.mail(uriMailTo);
            } else {
                desktop.mail();
            }
        } catch(IOException ioe) {
            ioe.printStackTrace();
        } catch(URISyntaxException use) {
            use.printStackTrace();
        }
    }

Java applications can open, edit, and print files from their associated application using the open(), edit(), and print() methods of the Desktop class, respectively.Java应用程序可以分别使用Desktop类的open()、edit()和print()方法从关联的应用程序中打开、编辑和打印文件。

private void onLaunchDefaultApplication(ActionEvent evt) {
        String fileName = txtFile.getText();
        File file = new File(fileName);
        
        try {
            switch(action) {
                case OPEN:
                    desktop.open(file);
                    break;
                case EDIT:
                    desktop.edit(file);
                    break;
                case PRINT:
                    desktop.print(file);
                    break;
            }
        } catch (IOException ioe) {
            //ioe.printStackTrace();
            System.out.println("Cannot perform the given operation 
                to the " + file + " file");
        }
    }

The complete code for this demo is available in the DesktopDemo.java file.DesktopDemo.java文件中提供了此演示的完整代码。

The Desktop API

The Desktop class allows Java applications to launch the native desktop applications that handle URIs or files.Desktop类允许Java应用程序启动处理URI或文件的本机桌面应用程序。

Examples That Use Desktop API使用桌面API的示例

The following table lists the example that uses the Desktop class integration.下表列出了使用Desktop类集成的示例。