I have the following code(Server is Tomcat/Linux).
// Send the local file over the current HTTP connection
FileInputStream fin = new FileInputStream(sendFile);
int readBlockSize;
int totalBytes=0;
while ((readBlockSize=fin.available())>0) {
byte[] buffer = new byte[readBlockSize];
fin.read(buffer, 0, readBlockSize);
outStream.write(buffer, 0, readBlockSize);
totalBytes+=readBlockSize;
}
With some files of type 3gp
When i attach the debugger, in line:
outStream.write(buffer, 0, readBlockSize);
it breaks out the while with the following error;
ApplicationFilterChain.internalDoFilter(ServletRequest, ServletResponse) line:299
And the file is not served.
Any clues?
Thanks
A.K.
You can't guarantee that InputStream.read(byte[], int, int) will actually read the desired number of bytes: it may read less. Even your call to available() will not provide that guarantee. You should use the return value from fin.read to find out how many bytes were actually read and only write that many to the output.
I would guess that the problem you see could be related to this. If the block read is less than the available size then your buffer will be partially filled and that will cause problems when you write too many bytes to the output.
Also, don't allocate a new array every time through the loop! That will result in a huge number of needless memory allocations that will slow your code down, and will potentially cause an OutOfMemoryError if available() returns a large number.
Try this:
int size;
int totalBytes = 0;
byte[] buffer = new byte[BUFFER_SIZE];
while ((size = fin.read(buffer, 0, BUFFER_SIZE)) != -1) {
outStream.write(buffer, 0, size);
totalBytes += size;
}
Avoiding these types of problems is why I start with Commons IO. If that's an option, your code would be as follows.
FileInputStream fin = new FileInputStream(sendFile);
int totalBytes = IOUtils.copy(fin, outStream);
No need reinventing the wheel.
It is possible that the .read() call returns less bytes than you requested. This means you need to use te returnvalue of .read() as argument to the .write() call:
int bytesRead = fin.read(buffer, 0, readBlockSize);
outStream.write(buffer, 0, bytesRead);
apart from this, it is better to pre-allocate a buffer and use it (your could could try to use a 2Gb buffer if your file is large :-))
byte[] buffer = new byte[4096]; // define a constant for this max length
while ((readBlockSize=fin.available())>0) {
if (4096 < readBlockSize) {
readBlockSise = 4096;
}
Related
I have an existing problem where I am using InputStreams and I want to increase the performance of reading from this channel. Therefore i read with a ReadableByteChannel.
As a result the reading is much faster with this code:
public static String readAll(InputStream is, String charset, int size) throws IOException{
try(ByteArrayOutputStream bos = new ByteArrayOutputStream()){
java.nio.ByteBuffer buffer = java.nio.ByteBuffer.allocate(size);
try(ReadableByteChannel channel = Channels.newChannel(is)){
int bytesRead = 0;
do{
bytesRead = channel.read(buffer);
bos.write(buffer.array(), 0, bytesRead);
buffer.clear();
}
while(bytesRead >= size);
}
catch(Exception ex){
ex.printStackTrace();
}
String ans = bos.toString(charset);
return ans;
}
}
The Problem is: It does not read to the end every time! If I try to read a File it works pretty good. If I read from a network Socket (to request a WebPage manually for example) it sometimes stops somewhere in between.
What can I do to read to the end?
I don't want to use something like this:
StringBuilder result = new StringBuilder();
while(true){
int ans = is.read();
if(ans == -1) break;
result.append((char)ans);
}
return result.toString();
because this implementation is slow.
I hope you can help me with my problem. maybe i have some mistake in my code.
This causes problem:
... } while (bytesRead >= size);
Reading from socket may return when at least one byte was read (or even if no bytes in case of non-blocking). So if there are not enough bytes in OS socket buffer, the condition will break the loop although obviously not full content was read. If the size identifies expected length to be received, implement total += bytesRead and break the loop when total reaches size. Or if you reach end of file of course...
Your copy loop is completely wrong. There's no reason why bytesRead should ever be >= size, and it misbehaves at end of stream. It should be something like this:
while ((bytesRead = channel.read(buffer)) > 0)
{
bos.write(buffer.array(), 0, bytesRead);
buffer.clear();
}
with suitable adjustments for limiting the transfer to size bytes, which are non-trivial.
But layering all this over an existing InputStream cannot possibly be 'much faster' tha using the InputStream directly, unless because of the premature termination. Unless your idea of use an InputStream is what you posted, which is horrifically slow. Try that with a 'BufferedInputStream.
I need to read out a given large file that contains 500000001 binaries. Afterwards I have to translate them into ASCII.
My Problem occurs while trying to store the binaries in a large array. I get the warning at the definition of the array ioBuf:
"The literal 16000000032 of type int is out of range."
I have no clue how to save these numbers to work with them! Has somebody an idea?
Here is my code:
public byte[] read(){
try{
BufferedInputStream in = new BufferedInputStream(new FileInputStream("data.dat"));
ByteArrayOutputStream bs = new ByteArrayOutputStream();
BufferedOutputStream out = new BufferedOutputStream(bs);
byte[] ioBuf = new byte[16000000032];
int bytesRead;
while ((bytesRead = in.read(ioBuf)) != -1){
out.write(ioBuf, 0, bytesRead);
}
out.close();
in.close();
return bs.toByteArray();
}
The maximum Index of an Array is Integer.MAX_VALUE and 16000000032 is greater than Integer.MAX_VALUE
Integer.MAX_VALUE = 2^31-1 = 2147483647
2147483647 < 16000000032
You could overcome this by checking if the Array is full and create another and continue reading.
But i'm not quite sure if your approach is the best way to perform this. byte[Integer_MAX_VALUE] is huge ;)
Maybe you can split the input file in smaller chunks process them.
EDIT: This is how you could read a single int of your file. You can resize the buffer's size to the amount of data you want to read. But you tried to read the whole file at once.
//Allocate buffer with 4byte = 32bit = Integer.SIZE
byte[] ioBuf = new byte[4];
int bytesRead;
while ((bytesRead = in.read(ioBuf)) != -1){
//if bytesRead == 4 you read 1 int
//do your stuff
}
If you need to declare a large constant, append an 'L' to it which indicates to the compiler that is a long constant. However, as mentioned in another answer you can't declare arrays that large.
I suspect the purpose of the exercise is to learn how to use the java.nio.Buffer family of classes.
I made some progress by starting from scratch! But I still have a problem.
My idea is to read up the first 32 bytes, convert them to a int number. Then the next 32 bytes etc. Unfortunately I just get the first and don't know how to proceed.
I discovered following method for converting these numbers to int:
public static int byteArrayToInt(byte[] b){
final ByteBuffer bb = ByteBuffer.wrap(b);
bb.order(ByteOrder.LITTLE_ENDIAN);
return bb.getInt();
}
so now I have:
BufferedInputStream in=null;
byte[] buf = new byte[32];
try {
in = new BufferedInputStream(new FileInputStream("ndata.dat"));
in.read(buf);
System.out.println(byteArrayToInt(buf));
in.close();
} catch (IOException e) {
System.out.println("error while reading ndata.dat file");
}
I'm trying to understand how inputstreams work. The following block of code is one of the many ways to read data from a text file:-
File file = new File("./src/test.txt");
InputStream input = new BufferedInputStream (new FileInputStream(file));
int data = 0;
while (data != -1) (-1 means we reached the end of the file)
{
data = input.read(); //if a character was read, it'll be turned to a bite and we get the integer representation of it so a is 97 b is 98
System.out.println(data + (char)data); //this will print the numbers followed by space then the character
}
input.close();
Now to use input.read(byte, offset, length) i have this code. I got it from here
File file = new File("./src/test.txt");
InputStream input = new BufferedInputStream (new FileInputStream(file));
int totalBytesRead = 0, bytesRemaining, bytesRead;
byte[] result = new byte[ ( int ) file.length()];
while ( totalBytesRead < result.length )
{
bytesRemaining = result.length - totalBytesRead;
bytesRead = input.read ( result, totalBytesRead, bytesRemaining );
if ( bytesRead > 0 )
totalBytesRead = totalBytesRead + bytesRead;
//printing integer version of bytes read
for (int i = 0; i < bytesRead; i++)
System.out.print(result[i] + " ");
System.out.println();
//printing character version of bytes read
for (int i = 0; i < bytesRead; i++)
System.out.print((char)result[i]);
}
input.close();
I'm assuming that based on the name BYTESREAD, this read method is returning the number of bytes read. In the documentation, it says that the function will try to read as many as possible. So there might be a reason why it wouldn't.
My first question is: What are these reasons?
I could replace that entire while loop with one line of code: input.read(result, 0, result.length)
I'm sure the creator of the article thought about this. It's not about the output because I get the same output in both cases. So there has to be a reason. At least one. What is it?
The documentation of read(byte[],int,int says that it:
Reads up to len bytes of data.
An attempt is made to read as many as len bytes
A smaller number may be read.
Since we are working with files that are right there in our hard disk, it seems reasonable to expect that the attempt will read the whole file, but input.read(result, 0, result.length) is not guaranteed to read the whole file (it's not said anywhere in the documentation). Relying in undocumented behaviors is a source for bugs when the undocumented behavior change.
For instance, the file stream may be implemented differently in other JVMs, some OS may impose a limit on the number of bytes that you may read at once, the file may be located in the network, or you may later use that piece of code with another implementation of stream, which doesn't behave in that way.
Alternatively, if you are reading the whole file in an array, perhaps you could use DataInputStream.readFully
About the loop with read(), it reads a single byte each time. That reduces performance if you are reading a big chunk of data, since each call to read() will perform several tests (has the stream ended? etc) and may ask the OS for one byte. Since you already know that you want file.length() bytes, there is no reason for not using the other more efficient forms.
Imagine you are reading from a network socket, not from a file. In this case you don't have any information about the total amount of bytes in the stream. You would allocate a buffer of fixed size and read from the stream in a loop. During one iteration of the loop you can't expect there are BUFFERSIZE bytes available in the stream. So you would fill the buffer as much as possible and iterate again, until the buffer is full. This can be useful, if you have data blocks of fixed size, for example serialized object.
ArrayList<MyObject> list = new ArrayList<MyObject>();
try {
InputStream input = socket.getInputStream();
byte[] buffer = new byte[1024];
int bytesRead;
int off = 0;
int len = 1024;
while(true) {
bytesRead = input.read(buffer, off, len);
if(bytesRead == len) {
list.add(createMyObject(buffer));
// reset variables
off = 0;
len = 1024;
continue;
}
if(bytesRead == -1) break;
// buffer is not full, adjust size
off += bytesRead;
len -= bytesRead;
}
} catch(IOException io) {
// stream was closed
}
ps. Code is not tested and should only point out, how this function can be useful.
You specify the amount of bytes to read because you might not want to read the entire file at once or maybe you couldn't or might not want to create a buffer as large as the file.
I have the following code to download a List of files. After downloading I compare the md5 of the online File with the downloaded.
They are similar when the download size is lower than 1024 bytes. For all over 1024bytes, there is an different md5 sum.
Now I don't know the reason. I think, it depends on the Array-Size with 1024 bytes? Maybe it writes on every time the full 1024 bytes to the file but then the question is, why does it work with files lower than 1kb??
String fileUrl= url_str;
URL url = new URL(fileUrl);
BufferedInputStream bufferedInputStream = new BufferedInputStream(url.openStream());
FileOutputStream fileOutputStream =new FileOutputStream(target);
BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(fileOutputStream, 1024);
byte data[] = new byte[1024];
while(bufferedInputStream.read(data, 0, 1024) >0 )
{
bufferedOutputStream.write(data);
}
bufferedOutputStream.close();
bufferedInputStream.close();
This is broken:
while(bufferedInputStream.read(data, 0, 1024) >0 )
{
bufferedOutputStream.write(data);
}
You're assuming that every read call fills up the entire buffer. You should use the return value of read:
int bytesRead;
while((bytesRead = bufferedInputStream.read(data, 0, 1024)) >0 )
{
bufferedOutputStream.write(data, 0, bytesRead);
}
(Additionally, you should be closing all your streams in finally blocks, but that's another matter.)
After the first read the data[] will be containing bytes. So during the last read the array will contain the last n bytes, and some bytes from the previous read. Actually you should check the return of the read. It indicates how many bytes has been read into the array, and write just that many bytes out.
I have this program that reads 2 Kb Data from a binary file adds some header to it and then writes it to a new file.
The code is
try {
FileInputStream fis = new FileInputStream(bin);
FileOutputStream fos = new FileOutputStream(bin.getName().replace(".bin", ".xyz"));
DataOutputStream dos=new DataOutputStream(fos);
fos.write(big, 0, big.length);
for (int n = 1; n <= pcount; n++) {
fis.read(file, mark, 2048);
mark = mark + 2048;
prbar.setValue(n);
prbar.setString("Converted packets:" + String.valueOf(n));
metas = "2048";
meta = metas.getBytes();
pc = String.valueOf(file.length).getBytes();
nval = String.valueOf(n).getBytes();
System.arraycopy(pc, 0, bmeta, 0, pc.length);
System.arraycopy(meta, 0, bmeta, 4, meta.length);
System.arraycopy(nval, 0, bmeta, 8, nval.length);
fos.write(bmeta, 0, bmeta.length);
fos.flush();
fos.write(file, 0, 2048);
fos.flush();
}
}catch (Exception ex) {
erlabel.setText(ex.getMessage());
}
First it should write the header and then the file.But the output file is full of data that does not belong to the file.It is writing some garbage data.What may be the problem?
It's not quite clear with some of the declarations missing, but it looks like your problem is with the fis.read() method: the second argument is an offset in the byte array, not the file (common mistake).
You probably want to use relative reads. You also need to check the return value from .read() to see how many bytes were actually read, before writing the buffer out.
The common idiom is:
InputStream is = ...
OutputStream os = ...
byte[] buf = new byte[2048];
int len;
while((len = is.read(buf)) != -1)
os.write(buf, 0, len);
is.close();
os.close();
Edit
That's a pretty weird way of writing out your metadata, I assume that's what the (unused) DataOutputStream is for?
You don't need to keep flushing the output stream, just close it when you're done.
In addition to what #Dmitri has pointed out, there is something seriously wrong with the way you are writing the metadata.
You are writing the metadata every time around the loop, which cannot be right.
You are essentially allocating 4 bytes for it, via "2048".getBytes(), then copying many more than 4 bytes into it, then writing the 4 bytes. This cannot be right either, in fact it should really be throwing ArrayIndexExceptions at you.
It looks as though the metadata is supposed to contain three binary integers. However you are putting String data into it. I suspect you should be using DataOutputStream.writeInt() directly for these fields, without all the String.valueOf()/getBytes() and System.arraycopy() nonsense.
I would like suggest to use lib community supported like apache common-io for IO features.
There are usefule classes and method;
org.apache.commons.io.DirectoryWalker;
org.apache.commons.io.FileUtils;
org.apache.commons.io.IOCase;
FileUtils.copyDirectory(from, to);
FileUtils.writeByteArrayToFile(file, data);
FileUtils.writeStringToFile(file, data);
FileUtils.deleteDirectory(dir);
FileUtils.forceDelete(dir);