I have parsed a JSON Object that was sent to my TOMCAT server using POST and turned it into a CSV file. I would like to send the CSV file back to the user. I am confused about how to send the file back because all the examples I have seen reference an actual file that is stored on the server - my file is built in memory and doesn't actually reference a file/file descriptor as far as I can tell.
//The doPost method has already generated the String[] - I then call generateCSV
protected void generateCSV(ArrayList<String[]> data, ServletOutputStream out,
HttpServletResponse response)
{
try{
BufferedWriter buff = new BufferedWriter(new OutputStreamWriter(out));
CSVWriter writer = new CSVWriter(buff);
writer.writeAll(data);
writer.close();
sendFile(response, out);
}catch(IOException | ServletException e){
e.printStackTrace();
}
}
protected void sendFile(HttpServletResponse response, ServletOutputStream outstream)throws ServletException, IOException
{
response.setContentType("application/octet-stream");
outstream.flush();
outstream.close();
}
What do you have to do to send a file to the user from a servlet?
Set the content-type.
Write out the bytes.
Seems to me you are doing this, but in the wrong order. Also, rather than using application/octet-stream you might want to actually tell the browser this is CSV. You might also want to give it a filename.
response.setContentType("text/csv");
response.setHeader("Content-Disposition","filename=whatever.csv");
BufferedWriter buff = new BufferedWriter(new OutputStreamWriter(out));
CSVWriter writer = new CSVWriter(buff);
writer.writeAll(data);
writer.close();
Related
I am trying to compress my response when the request header contains gzip in Accept-Encoding. However, adding following to app.properties only works when controller method is returning an object.
server.compression.enabled=true
server.compression.min-response-size=1
server.compression.mime-types=application/json,application/xml,text/html,text/xml,text/plain,application/javascript,text/css
I am writing directly to response stream. So, above compression properties don't work.
My method looks like this:
#GetMapping(path = "/something", produces = MediaType.TEXT_PLAIN_VALUE)
public void getSomething(#RequestParam(name = "paramA") String paramA,
HttpServletRequest request,
HttpServletResponse response) throws IOException {
PrintWriter writer = null;
if (request.getHeader("Accept-Encoding").contains("gzip")) {
writer = new PrintWriter(new OutputStreamWriter(new GZIPOutputStream(response.getOutputStream())));
response.addHeader(HttpHeaders.CONTENT_ENCODING, "gzip");
} else {
writer = response.getWriter();
}
final PrintWriter fwriter = writer;
someObjectInstance.getSomething(paramA).forEach(x -> {
fwriter.write(x.toString());
});
fwriter.flush();
}
When I curl the above method, I get an empty file.
I did try to use the GzipFilter by referring to the following link.
http://www.javablog.fr/javaweb-gzip-compression-protocol-http-filter-gzipresponsewrapper-gzipresponsewrapper.html, which works by the way.
However, the filter requires alot of boilerplate code. Is there a way I can make changes in controller method and solve the problem as in the link mentioned above.
Just realised I was not closing the writer.
After adding fwriter.close(); in the end, the problem was solved.
I saw many questions like the one I am asking, but they are not exactly about what I am looking for.
I am using Command pattern, and want to create PDF-file and download it. Creating is perfect, but when I want to download it, it's starts downloading and throws an exception.
java.lang.IllegalStateException: Cannot call sendRedirect() after the response has been committed
org.apache.jasper.JasperException: java.lang.IllegalStateException: getOutputStream() has already been called for this response
java.lang.IllegalStateException: getOutputStream() has already been called for this response
Here is my code from Command Pattern
#Override
public String execute(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException, AppException {
String fontPath = request.getServletContext().getRealPath(AppConstants.FONT_PATH);
DBManager db = DBManager.getInstance();
String ticketCode = request.getParameter("ticketCode");
String place = request.getParameter("place");
int amountTickets = Integer.valueOf(place);
String flightName = Encoding.encoding(request.getParameter("flightName"));
User user = (User) request.getSession().getAttribute("client");
String locale = (String) request.getServletContext().getAttribute("currentLocale");
db.updateFlightTickets(flightName, --amountTickets);
///////create pdf document and represent it to the byte array
ByteArrayOutputStream baos =ReportCreator.createReport(locale, fontPath, ticketCode, place, user,
db.getFlightByName(flightName));
response.setContentType("application/pdf");
response.setContentLength(baos.size());
response.setHeader("Content-Transfer-Encoding", "binary");
response.setHeader("Content-Disposition","attachment; filename=\"Ticket\"");
OutputStream os = response.getOutputStream();
baos.writeTo(os);
os.flush();
os.close();
return Path.SUCCESS;
}
Here is my "success page", sorry but can not add more, not enough reputation
<fmt:message key="success_jsp.label.success" />
And here is my servlet code
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
process(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
process(request, response);
}
private void process(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException {
String commandName = request.getParameter("command");
Command command = CommandContainer.get(commandName);
String forward = "";
try {
forward = command.execute(request, response);
} catch (AppException ex) {
request.setAttribute("errorMessage", ex.getMessage());
}
if (forward.equals(Path.SUCCESS)) {
response.sendRedirect(forward);
} else {
request.getRequestDispatcher(forward).forward(request, response);
}
}
Part of code in JSP, where click is calling the servlet
<td><button><fmt:message key="welcome_jsp.submit.buy_ticket" /></button></td>
How can i avoid it?
The exception says you are trying to working with the request/response once you redirect it or viceversa, and it's not valid.
Once you redirect a request, you cannot do anything else with the request/response, so getting the output stream and writing something to it is completely insane.
It's true about vice-versa situation, writing something and then redirect it will cause the browser will ignore the response data, or exception on server as I'm guessing you got.(but it depends on container)
So you either do not redirect the browser, or provide the pdf file with the target servlet/cgi where you are trying to redirect.
=================
And your current situation/problem:
Server sets the content-length, content-type,... and starts to write down some stream to the browser, since you haven't set any status, container will set default 200 OK which indicates there is some right response for the request.
Then browser will get some data(the pdf file) as 200 OK data(and consider it done), now how would you redirect the user once the response is almost done?!!?!!?!
I still do not understand why do you like to redirect a request when it's almost closed? you like to redirect the user after download complete? you cannot.
I receive an image in doPost method from a client application. I'm not supposed to store this image in any folder path, so i use the following code to store this image in session attribute as data byte.
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
String fileName = null;
fileName = request.getParameter("filename");
System.out.println("filename: " + fileName);
DataInputStream din = new DataInputStream(request.getInputStream());
byte[] data = new byte[0];
byte[] buffer = new byte[512];
int bytesRead;
while ((bytesRead = din.read(buffer)) > 0) {
// construct an array large enough to hold the data we currently have
byte[] newData = new byte[data.length + bytesRead];
// copy data that was previously read into newData
System.arraycopy(data, 0, newData, 0, data.length);
// append new data from buffer into newData
System.arraycopy(buffer, 0, newData, data.length, bytesRead);
// set data equal to newData in prep for next block of data
data = newData;
}
request.getSession().setAttribute("imageData", data);
}
I want to retrieve this from doGet method after its received. So, i am trying with the following doGet code to retrieve it.
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
byte[] data = (byte[]) request.getSession().getAttribute("imageData");
int len = data.length;
byte[] imageData = new byte[len];
for(int i=0; i < len; i++) {
imageData[i] = data[i];
}
response.setContentType("image/jpg");
response.getOutputStream().write(imageData);
response.getOutputStream().flush();
response.getOutputStream().close();
}
But, its NOT returning this image in doGet, when i call this servlet from an another client after some time.
Could someone please advise me, what I'm doing wrong here for not getting image in doGet?
I'm not supposed to store this image in any folder path, so i use the following code to store this image in session attribute as data byte.
...
But, its NOT returning this image in doGet, when i call this servlet from an other client after some time.
Session attributes are associated with exactly one client, so one client can not get the session attributes from an other client
You could store the image in the servlet context, like:
ServletContext context = request.getSession().getServletContext();
context.setAttribute("imageData", data);
Later, you can read the attribute from the servlet context.
Or, another possibility is to store the image in a static variable.
However, the image will be stored, although it is in memory. Maybe some Servlet Containers also store Servlet Context attributes on the hard disk.
I'm attempting to write a Java Servlet to receive binary data requests and reply to them, using HttpServletRequest.getOutputStream() and HttpServletResponse.getInputStream(). This is for a project which involves having a request sent by a Silverlight client to which this servlet responds to through an HTTP POST connection. For the time being, to test the Servlet I'm implementing a client in Java which I'm more familiar with than Silverlight.
The problem is that in my test project I send the data from a Servlet client as a byte array and expect to receive a byte array with the same length -- only it doesn't, and instead I'm getting a single byte. Therefore I'm posting here the relevant code snippets in the hopes that you might point me where I'm doing wrong and hopefully provide relevant bibliography to help me further.
So here goes.
The client servlet handles POST requests from a very simple HTML page with a form which I use as front-end. I'm not too worried about using JSP etc, instead I'm focused on making the inter-Servlet communication work.
// client HttpServlet invokes this method from doPost(request,response)
private void process(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String firstName = (String) request.getParameter("firstname");
String lastName = (String) request.getParameter("lastname");
String xmlRequest = "<MyRequest><Person><Name Firstname=\""+firstName+"\" Lastname=\""+lastName+"\" /></Person></MyRequest>";
OutputStream writer = null;
InputStream reader = null;
try {
URL url = new URL("http://localhost:8080/project/Server");
URLConnection conn = url.openConnection();
conn.setDoInput(true);
conn.setDoOutput(true);
writer = conn.getOutputStream();
byte[] baXml = xmlRequest.getBytes("UTF-8");
writer.write(baXml, 0,baXml.length);
writer.flush();
// perhaps I should be waiting here? how?
reader = conn.getInputStream();
int available = reader.available();
byte[] data = new byte[available];
reader.read(data,0,available);
String xmlResponse = new String(data,"UTF-8");
PrintWriter print = response.getWriter();
print.write("<html><body>Response:<br/><pre>");
print.write(xmlResponse);
print.write("</pre></body></html>");
print.close();
} finally {
if(writer!=null)
writer.close();
if(reader!=null)
reader.close();
}
}
The server servlet handles HTTP POST requests. This is done by receiving requests the requests from a client Servlet for testing purposes above, but in the future I intend to use it for clients in other languages (specifically, Silverlight).
// server HttpServlet invokes this method from doPost(request,response)
private void process(HttpServletRequest request, HttpServetResponse response)
throws ServletException, IOException {
ServletInputStream sis = null;
try {
sis = request.getInputStream();
// maybe I should be using a BufferedInputStream
// instead of the InputStream directly?
int available = sis.available();
byte[] input = new byte[available];
int readBytes = sis.read(input,0,available);
if(readBytes!=available) {
throw new ServletException("Oops! readBytes!=availableBytes");
}
// I ONLY GET 1 BYTE OF DATA !!!
// It's the first byte of the client message, a '<'.
String msg = "Read "+readBytes+" bytes of "
+available+" available from request InputStream.";
System.err.println("Server.process(HttpServletRequest,HttpServletResponse): "+msg);
String xmlReply = "<Reply><Message>"+msg+"</Message></Reply>";
byte[] data = xmlReply.getBytes("UTF-8");
ServletOutputStream sos = response.getOutputStream();
sos.write(data, 0,data.length);
sos.flush();
sos.close();
} finally {
if(sis!=null)
sis.close();
}
}
I have been sticking to byte arrays instead of using BufferInputStreams so far because I've not decided yet if I'll be using e.g. Base64-encoded strings to transmit data or if I'll be sending binary data as-is.
Thank you in advance.
To copy input stream to output stream use the standard way:
InputStream is=request.getInputStream();
OutputStream os=response.getOutputStream();
byte[] buf = new byte[1000];
for (int nChunk = is.read(buf); nChunk!=-1; nChunk = is.read(buf))
{
os.write(buf, 0, nChunk);
}
The one thing I can think of is that you are reading only request.getInputStream().available() bytes, then deciding that you have had everything. According to the documentation, available() will return the number of bytes that can be read without blocking, but I don't see any mention of whether this is actually guaranteed to be the entire content of the input stream, so am inclined to assume that no such guarantees are made.
I'm not sure how to best find out when there is no more data (maybe Content-Length in the request can help?) without risking blocking indefinitely at EOF, but I would try looping until having read all the data from the input stream. To test that theory, you could always scan the input for a known pattern that occurs further into the stream, maybe a > matching the initial < that you are getting.
I have an Excel file on the server side. How I can display it on client side browser using servlets?
Thanks in advance.
To the point: just get an InputStream of it somehow (FileInputStream is suitable) and write it to the OutputStream of the response the usual Java IO way. That's basically all. You'll only need to take care that you set the right response headers, so that the browser understands what to do with it. The Content-Type header will instruct the webbrowser what kind of file it is so that the browser knows which application to use to open it.
Here's a kickoff example:
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String filename = URLDecoder.decode(request.getPathInfo(), "UTF-8");
File file = new File("/path/to/files", filename);
response.setHeader("Content-Type", getServletContext().getMimeType(file.getName()));
response.setHeader("Content-Length", file.length());
response.setHeader("Content-Disposition", "inline; filename=\"" + file.getName() + "\"");
BufferedInputStream input = null;
BufferedOutputStream output = null;
try {
input = new BufferedInputStream(new FileInputStream(file));
output = new BufferedOutputStream(response.getOutputStream());
byte[] buffer = new byte[8192];
for (int length = 0; (length = input.read(buffer)) > 0;) {
output.write(buffer, 0, length);
}
} finally {
if (output != null) try { output.close(); } catch (IOException ignore) {}
if (input != null) try { input.close(); } catch (IOException ignore) {}
}
}
Map this servlet in web.xml on an url-pattern of /files/* so that you can get the excel file by http://example.com/contextname/files/filename.xls.
If it's actually an xlsx file, which isn't by default recognized by the average servletcontainer yet (the ServletContext#getMimeType() would then return application/octet-stream instead of the desired xlsx content type), then you need to add the following entry to the web.xml as well:
<mime-mapping>
<extension>xlsx</extension>
<mime-type>application/vnd.openxmlformats-officedocument.spreadsheetml.sheet</mime-type>
</mime-mapping>
For a more advanced example of a file servlet you may find this article useful as well, it supports under each download resumes as well.