Vaadin Web应用开发教程(22):UI组件-Upload组件

Upload 组件用于向服务器上传文件。它显示一个文件名输入框，一个文件选择按钮和一个上传确认按钮。

 

可以通过setButtonCaption 修改”Upload” 按钮的文字。对于”Browser” 按钮由于浏览器安全方面的考虑，难以修改它的外观，”Brower” 显示语言取决于浏览器本身。 因此如果你想保持”Upload” 语言显示的一致，你必须使用和“Browser”一样的语言。
通常情况上传的文件可以存放在文件系统，数据库或是临时存放在内存中，Upload 组件将上传的文件数据写到一个java.io.OutputStream 对象中，因此你可以使用你喜欢的方法来处理上传到服务器的文件。
使用Upload 组件，需要实现Upload.Receiver 接口来处理文件数据，它将在用户点击”upload”按钮后调用。
当文件上传结束后，成功与否Upload组件将触发Upload.FinishedEvent 事件。可以通过Upload.FinishedListener 接口来处理这个事件，事件参数包括文件名,MIME类型和文件长度。
下面的例子将上传的图像文件存放在/tmp/uploads 目录下 并显示最后上传的图像。

import java.io.File;import java.io.FileOutputStream;import java.io.OutputStream;import com.vaadin.terminal.FileResource;import com.vaadin.ui.*;public class MyUploader extends CustomComponent                        implements Upload.SucceededListener,                                   Upload.FailedListener,                                   Upload.Receiver {    Panel root;         // Root element for contained components.    Panel imagePanel;   // Panel that contains the uploaded image.    File  file;         // File to write to.    MyUploader() {        root = new Panel("My Upload Component");        setCompositionRoot(root);        // Create the Upload component.        final Upload upload =                new Upload("Upload the file here", this);        // Use a custom button caption instead of plain "Upload".        upload.setButtonCaption("Upload Now");        // Listen for events regarding the success of upload.        upload.addListener((Upload.SucceededListener) this);        upload.addListener((Upload.FailedListener) this);        root.addComponent(upload);        root.addComponent(new Label("Click 'Browse' to "+                "select a file and then click 'Upload'."));        // Create a panel for displaying the uploaded image.        imagePanel = new Panel("Uploaded image");        imagePanel.addComponent(                         new Label("No image uploaded yet"));        root.addComponent(imagePanel);    }    // Callback method to begin receiving the upload.    public OutputStream receiveUpload(String filename,                                      String MIMEType) {        FileOutputStream fos = null; // Output stream to write to        file = new File("/tmp/uploads/" + filename);        try {            // Open the file for writing.            fos = new FileOutputStream(file);        } catch (final java.io.FileNotFoundException e) {            // Error while opening the file. Not reported here.            e.printStackTrace();            return null;        }        return fos; // Return the output stream to write to    }    // This is called if the upload is finished.    public void uploadSucceeded(Upload.SucceededEvent event) {        // Log the upload on screen.        root.addComponent(new Label("File " + event.getFilename()                + " of type '" + event.getMIMEType()                + "' uploaded."));                // Display the uploaded file in the image panel.        final FileResource imageResource =                new FileResource(file, getApplication());        imagePanel.removeAllComponents();        imagePanel.addComponent(new Embedded("", imageResource));    }    // This is called if the upload fails.    public void uploadFailed(Upload.FailedEvent event) {        // Log the failure on screen.        root.addComponent(new Label("Uploading "                + event.getFilename() + " of type '"                + event.getMIMEType() + "' failed."));    }}