Multi tool use

Download file in Servlet

I am trying to download a file in a Servlet to the web client. I keep on getting this error.

Exception in thread "Thread-5" java.lang.NullPointerException
at org.apache.coyote.http11.Http11OutputBuffer.commit(Http11OutputBuffer.java:347)
at org.apache.coyote.http11.Http11Processor.prepareResponse(Http11Processor.java:1402)
at org.apache.coyote.AbstractProcessor.action(AbstractProcessor.java:327)
at org.apache.coyote.Response.action(Response.java:173)
at org.apache.coyote.http11.Http11OutputBuffer.doWrite(Http11OutputBuffer.java:219)
at org.apache.coyote.Response.doWrite(Response.java:541)
at org.apache.catalina.connector.OutputBuffer.realWriteBytes(OutputBuffer.java:351)
at org.apache.catalina.connector.OutputBuffer.flushByteBuffer(OutputBuffer.java:825)
at org.apache.catalina.connector.OutputBuffer.append(OutputBuffer.java:730)
at org.apache.catalina.connector.OutputBuffer.writeBytes(OutputBuffer.java:391)
at org.apache.catalina.connector.OutputBuffer.write(OutputBuffer.java:369)
at org.apache.catalina.connector.CoyoteOutputStream.write(CoyoteOutputStream.java:96)


Here is the code the code where I am downloading the file. The error happens on this line after 3 iterations:os.write(bufferData, 0, read);

os.write(bufferData, 0, read);

File desktop = File.createTempFile("dump",".csv");
mLink = desktop.getAbsolutePath();
FileWriter writer = new FileWriter(desktop);
mMessage = "Loading data to CSV to ";
ICsvListWriter csvWriter = null;
try {
csvWriter = new CsvListWriter(writer,
CsvPreference.STANDARD_PREFERENCE);

for (int i = 0; i < csvMatrix.size(); i++) {
csvWriter.write(csvMatrix.get(i));
}

} catch (IOException e) {
e.printStackTrace(); // TODO handle exception properly
mMessage = e.getLocalizedMessage();
} finally {
try {
csvWriter.close();


} catch (IOException e) {
e.printStackTrace();
mMessage = e.getLocalizedMessage();
}
}

// reads input file from an absolute path
String fileName =mLink;
if(fileName == null || fileName.equals("")){
throw new ServletException("File Name can't be null or empty");
}
File file = new File(mLink);
if(!file.exists()){
throw new ServletException("File doesn't exists on server.");
}
System.out.println("File location on server::"+file.getAbsolutePath());
ServletContext ctx = getServletContext();
InputStream fis = new FileInputStream(file);
String mimeType = ctx.getMimeType(file.getAbsolutePath());
mResponce.setContentType(mimeType != null? mimeType:"application/octet-stream");
mResponce.setContentLength((int) file.length());
mResponce.setHeader("Content-Disposition", "attachment; filename="" + fileName + """);

ServletOutputStream os = mResponce.getOutputStream();
byte bufferData = new byte[1024];
int read=0;
while((read = fis.read(bufferData))!= -1){
os.write(bufferData, 0, read);
}
os.flush();
os.close();
fis.close();
System.out.println("File downloaded at client successfully");


1 Answer
1

According to you if error is in this code

ServletOutputStream os = mResponce.getOutputStream();
byte bufferData = new byte[1024];
int read=0;
while((read = fis.read(bufferData))!= -1){
os.write(bufferData, 0, read);
}


then try this one

OutputStream out = mResponce.getOutputStream();
int i;
while ((i = fis.read()) != -1) {
out.write(i);
}
fis.close()


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