3.8 renderFile file download

1. Basic Usage of renderFile

The renderFile series of methods are used for file downloads.

The renderFile method uses a baseDownloadPath parameter as the base path to locate the file. In a standard maven project setup, this parameter defaults to the directory: src/main/webapp/download.

Here's how to use it under the default configuration:

// The final downloaded file will be: src/main/webapp/download/file.zip
renderFile("file.zip");
 
// The final downloaded file will be: src/main/webapp/download/abc/def/file.zip
renderFile("abc/deb/file.zip");

As shown above, the final downloaded file is always: baseDownloadPath + the parameter passed into renderFile.

The existence of baseDownloadPath effectively fixes a base path. renderFile always uses this path as the base to locate the file.

2. Configuring baseDownloadPath

baseDownloadPath can also be freely configured in configConstant(Constants me). For example:

me.setBaseDownloadPath("files");

In the context of a standard maven project, the baseDownloadPath value from the configuration above will point to the directory src/main/webapp/files.

Additionally, baseDownloadPath can also be configured as an absolute path, allowing it to point outside the project. For example:

// For Linux/Mac systems, paths starting with "/" are absolute paths.
me.setBaseDownloadPath("/var/download");
 
// For Windows systems, paths starting with a drive letter are also absolute paths.
me.setBaseDownloadPath("D:/download");

In the configuration above, in Linux, paths that start with "/" are considered absolute. So, renderFile will look for the download file under the "/var/download" path.

This kind of configuration allows separation between project resources and download resources. It's also beneficial for cluster deployment (single-machine multi-instance deployment) where multiple nodes can share the same directory and the same set of downloadable files.

3. renderFile(File file)

The renderFile(File file) method directly uses the File parameter to get the download file, freeing it from the constraints of baseDownloadPath. It can point to a file located anywhere, like:

String file = "D:/my-project/share/files/jfinal-all.zip";
renderFile(new File(file));

As shown, the File points to a file at an arbitrary location, bypassing the constraints of baseDownloadPath.

4. Renaming the Download File

If you don't want to use the original filename of the download file, you can specify a new download filename:

renderFile("OldFileName.txt", "NewFileName.txt");

In this way, users downloading the file will see it as "NewFileName.txt", regardless of its original name on the server.