VaadinWeb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&＃xff0c;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&＃xff0c;难以修改它的外观&＃xff0c;”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&＃xff0c;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&＃xff0c;数据库或是临时存放在内存中&＃xff0c;Upload 组件将上传的文件数据写到一个java.io.OutputStream 对象中&＃xff0c;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&＃xff0c;需要实现Upload.Receiver 接口来处理文件数据&＃xff0c;它将在用户点击”upload”按钮后调用。
当文件上传结束后&＃xff0c;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&＃xff0c;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 CustomComponentimplements 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 &＃61; new Panel("My Upload Component");setCompositionRoot(root);// Create the Upload component.final Upload upload &＃61;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 &＃39;Browse&＃39; to "&＃43;"select a file and then click &＃39;Upload&＃39;."));// Create a panel for displaying the uploaded image.imagePanel &＃61; 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 &＃61; null; // Output stream to write tofile &＃61; new File("/tmp/uploads/" &＃43; filename);try {// Open the file for writing.fos &＃61; 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 " &＃43; event.getFilename()&＃43; " of type &＃39;" &＃43; event.getMIMEType()&＃43; "&＃39; uploaded."));// Display the uploaded file in the image panel.final FileResource imageResource &＃61;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 "&＃43; event.getFilename() &＃43; " of type &＃39;"&＃43; event.getMIMEType() &＃43; "&＃39; failed."));}
}