Grails 3 Download Saved Documnets/Files (.pdf, .txt, .docx and others) Example.

How to Download different types of files using Grails 3.

If you want to use server-side file download for different types of files like pdf, txt, docx etc then there are different ways to do it.

We can use ServletOutputStream object for it as below:

    def download(){
            def filePath = "/opt/tomcat/webapps/savedFile/filename.pdf" //I am saving files on tomcat.
            def file = new File(filePath)
            if (file.exists()){
                response.setContentType("application/octet-stream")
                response.setHeader("Content-disposition", "filename=${file.getName()}")
                response.outputStream << file.bytes
            }else {
                //handle file not found messages.
            }
}

Here, contentType is "application/octet-stream" for all types of file. If you want to specified for specific one set contentType for specific one.

                response.setContentType("application/pdf")

Or you can do simply like this:

    def download(){
            def filePath = "/opt/tomcat/webapps/savedFile/filename.pdf" //I am saving files on tomcat.
            def file = new File(filePath)
            if (file.exists()){
                response.setContentType("application/octet-stream")
                response.setHeader("Content-disposition", "filename=${file.getName()}")
                response.outputStream << file.newInputStream()
            }else {
                //handle file not found messages.
            }
}

def download(){
            def filePath = "/opt/tomcat/webapps/savedFile/filename.pdf" //I am saving files on tomcat.
            def file = new File(filePath)
            if (file.exists()){
                response.setContentType("application/octet-stream")
                response.setHeader("Content-disposition", "filename=${file.getName()}")
                def outputStream = response.getOutputStream()
                outputStream << file.bytes
                outputStream.flush()
                outputStream.close()
            }else {
                //handle file not found messages.
            }
}

But in grails 3 latter version while deploying the war file to external tomcat(tomcat 7) server then we might get some class not found issue while downloading files.

Error 500: Internal Server Error
URI
/patient/download
Class
java.lang.ClassNotFoundException
Message
Handler dispatch failed; nested exception is java.lang.NoClassDefFoundError: javax/servlet/WriteListener
Caused by
javax.servlet.WriteListener

In order to solve this issue, we need to make the controller's action wrap with @GrailsCompileStatic annotation.

import grails.compiler.GrailsCompileStatic

@GrailsCompileStatic
def download(){
            def filePath = "/opt/tomcat/webapps/savedFile/filename.pdf" //I am saving files on tomcat.
            def file = new File(filePath)
            if (file.exists()){
                response.setContentType("application/octet-stream")
                response.setHeader("Content-disposition", "filename=${file.getName()}")
                def outputStream = response.getOutputStream()
                outputStream << file.bytes
                outputStream.flush()
                outputStream.close()
            }else {
                //handle file not found messages.
            }
}