com.vaadin.flow.server.streams.DownloadHandler API 24.8.3

com.vaadin.flow.server.streams.

All Superinterfaces:

ElementRequestHandler, Serializable

All Known Implementing Classes:

AbstractDownloadHandler, ClassDownloadHandler, FileDownloadHandler, InputStreamDownloadHandler, ServletResourceDownloadHandler

Functional Interface:

This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.

@FunctionalInterface public interface DownloadHandler extends ElementRequestHandler

Provides a flexible high-level abstraction for implementing file and arbitrary content downloads from server to client in Vaadin applications.

This interface can be implemented in two ways:

By creating a lambda expression that implements the handleDownloadRequest(DownloadEvent) method
By creating a child or anonymous class that implements this interface

The interface provides several factory methods for common download scenarios:

forFile(File) - for downloading files from the server
forClassResource(Class, String) - for downloading class resources
forServletResource(String) - for downloading servlet resources
fromInputStream(InputStreamDownloadCallback) - for downloading from input streams

Example:

 DownloadHandler.forFile(new File("/path/to/file.txt"));

All factory methods have overloads that allow adding a download progress listener and set a custom file name and URL postfix:

 DownloadHandler.forClassResource(MyView.class, "attachment-XYZ.txt",
         "attachment.txt", new TransferProgressListener() {
             @Override
             public void onComplete(TransferContext context,
                     long transferredBytes) {
                 // update UI on complete
             }
         });

If you need to write directly to an OutputStream, you can use a lambda expression with event.getOutputStream() to access the output stream:

 DownloadHandler handler = event -> {
     try (OutputStream out = event.getOutputStream()) {
         // Write your data to the output stream
         out.write(yourData);
     }
 };

Since:

24.8

Method Summary

Modifier and Type

Method

Description

static ClassDownloadHandler

forClassResource(Class<?> clazz, String resourceName)

Generate a download handler for class resource.

static ClassDownloadHandler

forClassResource(Class<?> clazz, String resourceName, TransferProgressListener listener)

Generate a download handler for class resource with the given progress listener.

static ClassDownloadHandler

forClassResource(Class<?> clazz, String resourceName, String fileNameOverride)

Generate a download handler for class resource with the given download name.

static ClassDownloadHandler

forClassResource(Class<?> clazz, String resourceName, String fileNameOverride, TransferProgressListener listener)

Generate a download handler for class resource with the given download name and progress listener.

static FileDownloadHandler

forFile(File file)

Get a download handler for serving given File.

static FileDownloadHandler

forFile(File file, TransferProgressListener listener)

Get a download handler for serving given File with the given progress listener.

static FileDownloadHandler

forFile(File file, String fileNameOverride)

Get a download handler for serving given File with the given download file name.

static FileDownloadHandler

forFile(File file, String fileNameOverride, TransferProgressListener listener)

Get a download handler for serving given File with the given download file name and progress listener.

static ServletResourceDownloadHandler

forServletResource(String path)

Generate a download handler for a servlet resource.

static ServletResourceDownloadHandler

forServletResource(String path, TransferProgressListener listener)

Generate a download handler for a servlet resource with the given progress listener.

static ServletResourceDownloadHandler

forServletResource(String path, String fileNameOverride)

Generate a download handler for a servlet resource with the given download file name.

static ServletResourceDownloadHandler

forServletResource(String path, String fileNameOverride, TransferProgressListener listener)

Generate a download handler for a servlet resource with the given download fileNameOverride and progress listener.

static InputStreamDownloadHandler

fromInputStream(InputStreamDownloadCallback callback)

Generate a function for downloading from a generated InputStream.

static InputStreamDownloadHandler

fromInputStream(InputStreamDownloadCallback callback, TransferProgressListener listener)

Generate a function for downloading from a generated InputStream with the given progress listener.

void

handleDownloadRequest(DownloadEvent event)

Method that is called when the client wants to download from the url stored for this specific handler registration.

default void

handleRequest(VaadinRequest request, VaadinResponse response, VaadinSession session, Element owner)

Request handler callback for handing client-server or server-client data transfer scoped to a specific (owner) element.

Methods inherited from interface com.vaadin.flow.server.streams.ElementRequestHandler
getDisabledUpdateMode, getUrlPostfix, isAllowInert

Method Details
- handleDownloadRequest
  
  void handleDownloadRequest(DownloadEvent event) throws IOException
  
  Method that is called when the client wants to download from the url stored for this specific handler registration.
  
  Parameters:
  
  event - download event containing the necessary data for writing the response
  
  Throws:
  
  IOException - if an IO error occurred during download
- handleRequest
  
  default void handleRequest(VaadinRequest request, VaadinResponse response, VaadinSession session, Element owner) throws IOException
  
  Description copied from interface: ElementRequestHandler
  
  Request handler callback for handing client-server or server-client data transfer scoped to a specific (owner) element. Note: when handling requests via this API, you need to take care of typical stream handling issues, e.g. exceptions yourself. However, you do not need to close the stream yourself, Flow will handle that for you when needed.
  
  Specified by:
  
  handleRequest in interface ElementRequestHandler
  
  Parameters:
  
  request - VaadinRequest request to handle
  
  response - VaadinResponse response to handle
  
  session - VaadinSession current VaadinSession
  
  owner - Element owner element
  
  Throws:
  
  IOException - if an IO error occurred during data transfer
- forFile
  
  static FileDownloadHandler forFile(File file)
  
  Get a download handler for serving given File.
  The downloaded file name is resolved as file.getName().
  
  Parameters:
  
  file - file to server for download
  
  Returns:
  
  DownloadHandler implementation for download a file
- forFile
  
  static FileDownloadHandler forFile(File file, String fileNameOverride)
  
  Get a download handler for serving given File with the given download file name.
  
  Parameters:
  
  file - file to server for download
  
  fileNameOverride - download file name that overrides file.getName() and also used as a download request URL postfix
  
  Returns:
  
  DownloadHandler implementation for download a file
- forFile
  
  static FileDownloadHandler forFile(File file, String fileNameOverride, TransferProgressListener listener)
  
  Get a download handler for serving given File with the given download file name and progress listener.
  
  Parameters:
  
  file - file to server for download
  
  fileNameOverride - download file name that overrides file.getName() and also used as a download request URL postfix
  
  listener - listener for transfer progress events
  
  Returns:
  
  DownloadHandler implementation for download a file
- forFile
  
  static FileDownloadHandler forFile(File file, TransferProgressListener listener)
  
  Get a download handler for serving given File with the given progress listener.
  The downloaded file name is resolved as file.getName().
  
  Parameters:
  
  file - file to server for download
  
  listener - listener for transfer progress events
  
  Returns:
  
  DownloadHandler implementation for download a file
- forClassResource
  
  static ClassDownloadHandler forClassResource(Class<?> clazz, String resourceName)
  
  Generate a download handler for class resource.
  For instance for the file resources/com/example/ui/MyData.json and class com.example.ui.MyData the definition would be forClassResource(MyData.class, "MyData.json").
  The downloaded file name is resolved as resourceName.
  
  Parameters:
  
  clazz - class for resource module
  
  resourceName - name of class resource
  
  Returns:
  
  DownloadHandler implementation for download a class resource
- forClassResource
  
  static ClassDownloadHandler forClassResource(Class<?> clazz, String resourceName, String fileNameOverride)
  
  Generate a download handler for class resource with the given download name.
  For instance for the file resources/com/example/ui/MyData.json and class com.example.ui.MyData the definition would be forClassResource(MyData.class, "MyData.json", "Data.json")
  
  Parameters:
  
  clazz - class for resource module
  
  resourceName - name of class resource
  
  fileNameOverride - download file name that overrides resourceName and also used as a download request URL postfix
  
  Returns:
  
  DownloadHandler implementation for download a class resource
- forClassResource
  
  static ClassDownloadHandler forClassResource(Class<?> clazz, String resourceName, String fileNameOverride, TransferProgressListener listener)
  
  Generate a download handler for class resource with the given download name and progress listener.
  For instance for the file resources/com/example/ui/MyData.json and class com.example.ui.MyData the definition would be forClassResource(MyData.class, "MyData.json", "Data.json")
  
  Parameters:
  
  clazz - class for resource module
  
  resourceName - name of class resource
  
  fileNameOverride - download file name that overrides resourceName and also used as a download request URL postfix
  
  listener - listener for transfer progress events
  
  Returns:
  
  DownloadHandler implementation for download a class resource
- forClassResource
  
  static ClassDownloadHandler forClassResource(Class<?> clazz, String resourceName, TransferProgressListener listener)
  
  Generate a download handler for class resource with the given progress listener.
  For instance for the file resources/com/example/ui/MyData.json and class com.example.ui.MyData the definition would be forClassResource(MyData.class, "MyData.json", "Data.json").
  The downloaded file name is resolved as resourceName.
  
  Parameters:
  
  clazz - class for resource module
  
  resourceName - name of class resource
  
  listener - listener for transfer progress events
  
  Returns:
  
  DownloadHandler implementation for download a class resource
- forServletResource
  
  static ServletResourceDownloadHandler forServletResource(String path)
  
  Generate a download handler for a servlet resource.
  For instance for the file webapp/WEB-INF/servlet.json the path would be /WEB-INF/servlet.json.
  The downloaded file name is resolved as the last segment in path.
  
  Parameters:
  
  path - the servlet path to the file
  
  Returns:
  
  DownloadHandler implementation for downloading a servlet resource
- forServletResource
  
  static ServletResourceDownloadHandler forServletResource(String path, String fileNameOverride)
  
  Generate a download handler for a servlet resource with the given download file name.
  For instance for the file webapp/WEB-INF/servlet.json the path would be /WEB-INF/servlet.json
  File name override is appended to the download url as the logical name of the target file.
  
  Parameters:
  
  path - the servlet path to the file
  
  fileNameOverride - download file name that overrides the name taken from path and also used as a download request URL postfix
  
  Returns:
  
  DownloadHandler implementation for downloading a servlet resource
- forServletResource
  
  static ServletResourceDownloadHandler forServletResource(String path, String fileNameOverride, TransferProgressListener listener)
  
  Generate a download handler for a servlet resource with the given download fileNameOverride and progress listener.
  For instance for the file webapp/WEB-INF/servlet.json the path would be /WEB-INF/servlet.json
  File name override is appended to the download url as the logical name of the target file.
  
  Parameters:
  
  path - the servlet path to the file
  
  fileNameOverride - download file name that overrides the name taken from path and also used as a download request URL postfix
  
  listener - listener for transfer progress events
  
  Returns:
  
  DownloadHandler implementation for downloading a servlet resource
- forServletResource
  
  static ServletResourceDownloadHandler forServletResource(String path, TransferProgressListener listener)
  
  Generate a download handler for a servlet resource with the given progress listener.
  For instance for the file webapp/WEB-INF/servlet.json the path would be /WEB-INF/servlet.json.
  
  Parameters:
  
  path - the servlet path to the file
  
  listener - listener for transfer progress events
  
  Returns:
  
  DownloadHandler implementation for downloading a servlet resource
- fromInputStream
  
  static InputStreamDownloadHandler fromInputStream(InputStreamDownloadCallback callback)
  
  Generate a function for downloading from a generated InputStream.
  DownloadResponse instances can be created using various factory methods or with new operator.
  
  Parameters:
  
  callback - a function that will be called on download
  
  Returns:
  
  DownloadHandler implementation for download from an input stream
- fromInputStream
  
  static InputStreamDownloadHandler fromInputStream(InputStreamDownloadCallback callback, TransferProgressListener listener)
  
  Generate a function for downloading from a generated InputStream with the given progress listener.
  DownloadResponse instances can be created using various factory methods or with new operator.
  
  Parameters:
  
  callback - a function that will be called on download
  
  listener - listener for transfer progress events
  
  Returns:
  
  DownloadHandler implementation for download from an input stream

com.vaadin.flow.server.streams.

Interface DownloadHandler

Method Summary

Methods inherited from interface com.vaadin.flow.server.streams.ElementRequestHandler

Method Details

handleDownloadRequest

handleRequest

forFile

forFile

forFile

forFile

forClassResource

forClassResource

forClassResource

forClassResource

forServletResource

forServletResource

forServletResource

forServletResource

fromInputStream

fromInputStream