I have a class to process some files which is uploaded zipped.
And a method to unzip and fill a HashMap and convert to an Collection.unmodifiableMap.
public class MyClass extends HttpServlet {
...
private Map<String, String> rnaseqfiles = new HashMap<>();
...
private void processZipFile(String zipfile) throws Exception {
String fileName = zipfile;
byte[] buffer = new byte[1024];
try (ZipInputStream zis = new ZipInputStream(new FileInputStream(fileName))) {
ZipEntry zipEntry = zis.getNextEntry();
while (zipEntry != null) {
File newFile = new File(diretorio, zipEntry.toString());
if (zipEntry.isDirectory()) {
if (!newFile.isDirectory() && !newFile.mkdirs()) {
throw new IOException("Failed to create directory " + newFile);
}
} else {
FileOutputStream fos = new FileOutputStream(newFile);
int len;
while ((len = zis.read(buffer)) > 0) {
fos.write(buffer, 0, len);
}
fos.close();
rnaseqfiles.put(zipEntry.toString(), newFile.getAbsolutePath());
}
zipEntry = zis.getNextEntry();
}
rnaseqfiles = Collections.unmodifiableMap(rnaseqfiles);
zis.closeEntry();
zis.close();
}
}
...
}
When I test with a small example, it works nicely, but when I try with the real case I got this kind of error.
java.lang.UnsupportedOperationException
at java.base/java.util.Collections$UnmodifiableMap.put(Collections.java:1457)
I found some hints to deal with it but I don't know exactly what to do.
Any help is appreciated
servlets are quite annoying. Think of the notion that any given servlet is likely going to run many times, and probably many times simultaneously, as various users hit your site.
They are the worst of both worlds: The servlet spec does not guarantee that the system initializes a new object for every request (meaning, it is possible that many different requests, some even simultaneous, are all using the same fields), but it als does not guarantee the opposite either: The system is free to do so.
Conclusion: Fields in servlets are pretty much useless. But you have one, and it's causing troubles: One 'run' overwrites your mutable hashmap with an immutable one, and then the next servlet tries to add stuff to this now immutable map.
The fix is generally to just get rid of servlets. There are better ways to write web apps these days, such as spark, DropWizard, Spring, and many others.
If you insist, then your servlets should not have any fields. If you desire them, your servlet code should simply make a new object and then invoke whatever you want there - your doGet and friends are mostly just oneliners of the form new ActualHandler(req, res).go() or similar. Now you actually have one instance per request.
Or, just.. write the code so that no fields are needed. I don't see why you need a field here, for example. Your current code does;
Receive the request and parse stuff out (you didn't paste this part)
That code evidently invokes processZipFile which returns nothing, but conveys data back using a field. (This does not work in servlets).
Your request handling code then uses that field for stuff.
Seems easy to replace that - don't have a field, have the processZipFile method return that map instead.
Related
Is there anyway to reuse an inputStream by changing its content? (Without new statement).
For instance, I was able to something very close to my requirement, but not enough
In the following code I am using a SequenceInputStream, and everytime I am adding a new InputStream to that sequence.
But I would like to do the same thing by using the same inputStream (I don't care which implementation of InputStream).
I thought about mark()/reset() APIs, but i still need to change the content to be read.
The idea to avoid new InputStream creations is because of performance issues
//Input Streams
List<InputStream> inputStreams = new ArrayList<InputStream>();
try{
//First InputStream
byte[] input = new byte[]{24,8,102,97};
inputStreams.add(new ByteArrayInputStream(input));
Enumeration<InputStream> enu = Collections.enumeration(inputStreams);
SequenceInputStream is = new SequenceInputStream(enu);
byte [] out = new byte[input.length];
is.read(out);
for (byte b : out){
System.out.println(b);//Will print 24,8,102,97
}
//Second InputStream
input = new byte[]{ 4,66};
inputStreams.add(new ByteArrayInputStream(input));
out = new byte[input.length];
is.read(out);
for (byte b : out){
System.out.println(b);//will print 4,66
}
is.close();
}catch (Exception e){//
}
No, You can't restart reading the input stream after it reaches to the end of the stream as it is uni-directional i.e. moves only in single direction.
But Refer below links, they may help:
How to Cache InputStream for Multiple Use
Getting an InputStream to read more than once, regardless of markSupported()
You could create your own implementation (subclass) of InputStream that would allow what you require. I doubt there is an existing implementation of this.
I highly doubt you'll get any measurable performance boost from this though, there's not much of logic in e.g. FileInputStream that you wouldn't need to perform anyways, and Java is well optimized for garbage-collecting short-lived objects.
I want to create a link that would initiate a file download which would be asynchronous to the page itself, i.e. I want the page not to be locked during the file download. Should I make it be initiated outside wicket? Or is there something inside wicket that would let me set up a resource stream which would bypass the page locks?
Things I tried:
DownloadLink - locks the page, as stated in its doc. This was my starting point.
ResourceLink - did not state the locking explicitly in the doc, so I tried this, but it also locked the page.
At this point I've investigated the code of both links a bit and noticed they both schedule the download via ResourceStreamRequestHandler. Expecting that his kind of behavior could be just handler-specific I've attempted to schedule a custom handler I've written:
private void sendFile(final File file) throws IOException {
IRequestHandler fileDownloadHandler = new IRequestHandler() {
#Override
public void respond(IRequestCycle requestCycle) {
WebResponse response = (WebResponse) requestCycle.getResponse();
OutputStream outStream = response.getOutputStream();
response.setContentType("audio/x-wav");
response.setContentLength((int)file.length());
String fileName = "Somethingsomething.wav";
// sets HTTP header
response.setHeader("Content-Disposition", "attachment; filename=\"" + fileName + "\"");
byte[] byteBuffer = new byte[1024];
DataInputStream in = null;
try {
in = new DataInputStream(new FileInputStream(file));
int length = 0;
// reads the file's bytes and writes them to the response stream
while ((in != null) && ((length = in.read(byteBuffer)) != -1))
{
outStream.write(byteBuffer,0,length);
}
in.close();
outStream.close();
} catch (IOException e) {
throw new PortalError("IOException trying to write the response", e);
}
}
#Override
public void detach(IRequestCycle requestCycle) {
}
};
getRequestCycle().scheduleRequestHandlerAfterCurrent(fileDownloadHandler);
}
This did not quite work either, so I've investigated further. I've noticed that unlike I expected, the "scheduled" request handlers would not get executed on a separate request, as I expected, but on the same one. I figured that it must be that the page gets locked for the first handler and then remains locked while the second one is executing as well. So I've attempted to force the download handler into a separate request (via an ajax behaviour):
public void startDownload(AjaxRequestTarget target) throws DownloadTargetNotFoundException{
target.appendJavaScript("setTimeout(\"window.location.href='" + getCallbackUrl() + "'\", 100);");
}
#Override
public void onRequest() {
sendFile(getFile());
logger.debug("Download initiated");
}
I've found this here and hoped it could potentially be what I've been looking for. However, unsurprisingly so, the page gets locked still (I would imagine because the behaviour still has to be retrieved from the page, for which the page lock has to be acquired).
I'm at a loss where I should be looking next, especially after all this time trying to get a simple download link working. I was considering creating another web filter one layer above wicket, which could be signaled from within wicket to create the download after the wicket filter is finished with its work (and hence the page lock is already released), but that seems a bit excessive for a task like this.
Any suggestions are welcome.
You have to download from a resource, see
http://wicketinaction.com/2012/11/uploading-files-to-wicket-iresource/ and read http://wicket.apache.org/guide/guide/resources.html
I get a file personHashMap.ser with a HashMap in it. Here's the code how i create it:
String file_path = ("//releasearea/ToolReleaseArea/user/personHashMap.ser");
public void createFile(Map<String, String> newContent) {
try{
File file = new File(file_path);
FileOutputStream fos=new FileOutputStream(file);
ObjectOutputStream oos=new ObjectOutputStream(fos);
oos.writeObject(newContent);
oos.flush();
oos.close();
fos.close();
}catch (Exception e){
System.err.println("Error in FileWrite: " + e.getMessage());
}
}
Now i want, when the program is running, that all five minutes update the file personHashMap.ser only with the content which changed. So the method i called:
public void updateFile(Map<String, String> newContent) {
Map<String, String> oldLdapContent = readFile();
if(!oldLdapContent.equals(ldapContent)){ // they arent the same,
// so i must update the file
}
}
But now i haven't any ideas how i can realise that.
And is it better for the performance to update only the new content or should i clean the full file and insert the new list again?
Hope you can Help me..
EDIT:
The HashMap includes i.e street=Example Street.
But now, the new street called New Example Street. Now i must update the HashMap in the File. So i can't just append the new content...
Firstly HashMap isn't really an appropriate choice. It's designed for in-memory usage, not serialization (though of course it can be serialized in the standard way). But if it's just 2kb, then go ahead and write the whole thing rather than the updated data.
Second, you seem to be overly worried about performance of this rather trivial method (for 2kb the write will take mere milliseconds). I would be worried more about consistency and concurrency issues. I suggest you look into using a lightweight database such as JavaDB or h2.
Use the constructor FileOutputStream(File file, boolean append), set the boolean append to true. It will append the text in the existing file.
You can call the updateFile method in a loop and then call sleep for 5 minutes (5*60*1000 ms).
Thread.Sleep(300000); // sleep for 5 minutes
To append to your already existing file you can use :
FileOutputStream fooStream = new FileOutputStream(file, true);
I'm a newbie in Spring Batch, and I would appreciate some help to resolve this situation: I read some files with a MultiResourceItemReader, make some marshalling work, in the ItemProcessor I receive a String and return a Map<String, List<String>>, so my problem is that in the ItemWriter I should iterate the keys of the Map and for each one of them generate a new file containing the value associated with that key, can someone point me out in the right direction in order to create the files?
I'm also using a MultiResourceItemWriter because I need to generates files with a maximum of lines.
Thanks in advance
Well, finaly got a solution, I'm not really excited about it but it's working and I don't have much more time, so I've extended the MultiResourceItemWriter and redefined the "write" method, processing the map's elements and writing the files by myself.
In case anyone out there needs it, here it is.
#Override
public void write(List items) throws Exception {
for (Object o : items) {
//do some processing here
writeFile(anotherObject);
}
private void writeFile (AnotherObject anotherObject) throws IOException {
File file = new File("name.xml");
boolean restarted = file.exists();
FileUtils.setUpOutputFile(file, restarted, true, true);
StringBuffer sb = new StringBuffer();
sb.append(xStream.toXML(anotherObject));
FileOutputStream os = new FileOutputStream(file, true);
BufferedWriter bufferedWriter = new BufferedWriter(new OutputStreamWriter(os, Charset.forName("UTF-8")));
bufferedWriter.write(sb.toString());
bufferedWriter.close();
}
And that's it, I want to believe that there is a better option that I don't know, but for the moment this is my solution. If anyone knows how can I enhance my implementation, I'd like to know it.
I'm writing to the browser window using servletResponse.getWriter().write(String).
But how do I clear the text which was written previously by some other similar write call?
The short answer is, you cannot -- once the browser receives the response, there is no way to take it back. (Unless there is some way to abnormally stop a HTTP response to cause the client to reload the page, or something to that extent.)
Probably the last place a response can be "cleared" in a sense, is using the ServletResponse.reset method, which according to the Servlet Specification, will reset the buffer of the servlet's response.
However, this method also seems to have a catch, as it will only work if the buffer has not been committed (i.e. sent to the client) by the ServletOutputStream's flush method.
You cannot. The best thing is to write to a buffer (StringWriter / StringBuilder) and then you can replace the written data any time. Only when you know for sure what is the response you can write the buffer's content to the response.
In the same matter, and reason to write the response this way and not to use some view technology for your output such as JSP, Velocity, FreeMarker, etc.?
If you have an immediate problem that you need to solve quickly, you could work around this design problem by increasing the size of the response buffer - you'll have to read your application server's docs to see if this is possible. However, this solution will not scale as you'll soon run into out-of-memory issues if you site traffic peaks.
No view technology will protect you from this issue. You should design your application to figure out what you're going to show the user before you start writing the response. That means doing all your DB access and business logic ahead of time. This is a common issue I've seen with convoluted system designs that use proxy objects that lazily access the database. E.g. ORM with Entity relationships are bad news if accessed from your view layer! There's not much you can do about an exception that happens 3/4 of the way into a rendered page.
Thinking about it, there might be some way to inject a page redirect via AJAX. Anyone ever heard of a solution like that?
Good luck with re-architecting your design!
I know the post is pretty old, but just thought of sharing my views on this.
I suppose you could actually use a Filter and a ServletResponseWrapper to wrap the response and pass it along the chain.
That is, You can have an output stream in the wrapper class and write to it instead of writing into the original response's output stream... you can clear the wrapper's output stream as and when you please and you can finally write to the original response's output stream when you are done with your processing.
For example,
public class MyResponseWrapper extends HttpServletResponseWrapper {
protected ByteArrayOutputStream baos = null;
protected ServletOutputStream stream = null;
protected PrintWriter writer = null;
protected HttpServletResponse origResponse = null;
public MyResponseWrapper( HttpServletResponse response ) {
super( response );
origResponse = response;
}
public ServletOutputStream getOutputStream()
throws IOException {
if( writer != null ) {
throw new IllegalStateException( "getWriter() has already been " +
"called for this response" );
}
if( stream == null ) {
baos = new ByteArrayOutputStream();
stream = new MyServletStream(baos);
}
return stream;
}
public PrintWriter getWriter()
throws IOException {
if( writer != null ) {
return writer;
}
if( stream != null ) {
throw new IllegalStateException( "getOutputStream() has already " +
"been called for this response" );
}
baos = new ByteArrayOutputStream();
stream = new MyServletStream(baos);
writer = new PrintWriter( stream );
return writer;
}
public void commitToResponse() {
origResponse.getOutputStream().write(baos.toByteArray());
origResponse.flush();
}
private static class MyServletStream extends ServletOutputStream {
ByteArrayOutputStream baos;
MyServletStream(ByteArrayOutputStream baos) {
this.baos = baos;
}
public void write(int param) throws IOException {
baos.write(param);
}
}
//other methods you want to implement
}