I recently tried reading data from inputStream.
int length = getHeader("Content-Length");
byte[] buffer = new byte [length];
BufferedInputStream stream = new BufferedInputStream (servletRequest.getInputStream());
stream.read(buffer);
It was truncating my data somehow. When I tried following
buffer = IOUtils.toByteArray(servletRequest.getInputStream());
It worked perfectly.
Can anybody give me insights on what could be the issue ?
#Gaurav_Joshi
The BufferedInputStream constructor that takes one argument InputStream uses DEFAULT_BUFFER_SIZE, which could be less than the actual size of your input stream.
public BufferedInputStream(InputStream in) {
this(in, DEFAULT_BUFFER_SIZE);
}
I made an InputStream Object from a file and a InputStreamReader from that.
InputStream ips = new FileInputStream("c:\\data\\input.txt");
InputStreamReader isr = new InputStreamReader(ips);
I will basically read data in the form of bytes to a buffer but when there comes a time when i should read in chars I will 'switch mode' and read with InputStreamReader
byte[] bbuffer = new byte[20];
char[] cbuffer = new char[20];
while(ips.read(buffer, 0, 20)!=-1){
doSomethingWithbBuffer(bbuffer);
// check every 20th byte and if it is 0 start reading as char
if(bbuffer[20] == 0){
while(isr.read(cbuffer, 0, 20)!=-1){
doSomethingWithcBuffer(cbuffer);
// check every 20th char if its # return to reading as byte
if(cbuffer[20] == '#'){
break;
}
}
}
}
is this a safe way to read files that have mixed char and byte data?
no, this is not safe. the InputStreamReader may read "too much" data from the underlying stream (it uses internal buffers) and corrupt your attempt to read from the underlying byte stream. You can use something like DataInputStream if you want to mix reading characters and bytes.
Alternately, just read the data as bytes and use the correct character encoding to convert those bytes to characters/Strings.
FileInputStream fin = new FileInputStream(path);
BufferedInputStream bin = new BufferedInputStream(fin);
byte[] inputByte1= new byte[500];
byte[] inputByte2= new byte[500];
byte[] inputByte3 =new byte[34];
bin.read(inputByte1);
bin.read(inputByte2);
bin.read(inputByte3);
Let's say the file had only 400 bytes. How can I detect it?
I know that I could check if (bin.read(inputByte1)!=500)
But this looks really ugly to write in each line.
My main questions is:
How to detect if before filling some array the buffer was done.
I do not want to do bin.read() for each byte and check bin.read!=-1.
First, on a Windows based system you need to escape the \ when you use it as a path separator. Next, you could use a FileInputStream (which you could wrap with a BufferedInputStream). Finally, you should close the InputStream when you're done (or you risk leaking file handles, sockets or some other resource). You might use a try-with-resources statement. Putting it all together, it might look something like
File f = new File("c:\\test\\test.txt");
try (InputStream is = new BufferedInputStream(new FileInputStream(f))) {
int val;
while ((val = is.read()) != -1) {
System.out.println((byte) val);
}
} catch (IOException ioe) {
ioe.printStackTrace();
}
I would recommend a DataInputStream over a BufferedInputStream over a FileInputStream. That way you can use the readFully() method to read exactly as many bytes as you need each time without having to loop.
c:\test\test.txt
Use forward slashes in Java:
c:/test/test.txt
Someone explain to me what InputStream and OutputStream are?
I am confused about the use cases for both InputStream and OutputStream.
If you could also include a snippet of code to go along with your explanation, that would be great. Thanks!
The goal of InputStream and OutputStream is to abstract different ways to input and output: whether the stream is a file, a web page, or the screen shouldn't matter. All that matters is that you receive information from the stream (or send information into that stream.)
InputStream is used for many things that you read from.
OutputStream is used for many things that you write to.
Here's some sample code. It assumes the InputStream instr and OutputStream osstr have already been created:
int i;
while ((i = instr.read()) != -1) {
osstr.write(i);
}
instr.close();
osstr.close();
InputStream is used for reading, OutputStream for writing. They are connected as decorators to one another such that you can read/write all different types of data from all different types of sources.
For example, you can write primitive data to a file:
File file = new File("C:/text.bin");
file.createNewFile();
DataOutputStream stream = new DataOutputStream(new FileOutputStream(file));
stream.writeBoolean(true);
stream.writeInt(1234);
stream.close();
To read the written contents:
File file = new File("C:/text.bin");
DataInputStream stream = new DataInputStream(new FileInputStream(file));
boolean isTrue = stream.readBoolean();
int value = stream.readInt();
stream.close();
System.out.printlin(isTrue + " " + value);
You can use other types of streams to enhance the reading/writing. For example, you can introduce a buffer for efficiency:
DataInputStream stream = new DataInputStream(
new BufferedInputStream(new FileInputStream(file)));
You can write other data such as objects:
MyClass myObject = new MyClass(); // MyClass have to implement Serializable
ObjectOutputStream stream = new ObjectOutputStream(
new FileOutputStream("C:/text.obj"));
stream.writeObject(myObject);
stream.close();
You can read from other different input sources:
byte[] test = new byte[] {0, 0, 1, 0, 0, 0, 1, 1, 8, 9};
DataInputStream stream = new DataInputStream(new ByteArrayInputStream(test));
int value0 = stream.readInt();
int value1 = stream.readInt();
byte value2 = stream.readByte();
byte value3 = stream.readByte();
stream.close();
System.out.println(value0 + " " + value1 + " " + value2 + " " + value3);
For most input streams there is an output stream, also. You can define your own streams to reading/writing special things and there are complex streams for reading complex things (for example there are Streams for reading/writing ZIP format).
From the Java Tutorial:
A stream is a sequence of data.
A program uses an input stream to read data from a source, one item at a time:
A program uses an output stream to write data to a destination, one item at time:
The data source and data destination pictured above can be anything that holds, generates, or consumes data. Obviously this includes disk files, but a source or destination can also be another program, a peripheral device, a network socket, or an array.
Sample code from oracle tutorial:
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
public class CopyBytes {
public static void main(String[] args) throws IOException {
FileInputStream in = null;
FileOutputStream out = null;
try {
in = new FileInputStream("xanadu.txt");
out = new FileOutputStream("outagain.txt");
int c;
while ((c = in.read()) != -1) {
out.write(c);
}
} finally {
if (in != null) {
in.close();
}
if (out != null) {
out.close();
}
}
}
}
This program uses byte streams to copy xanadu.txt file to outagain.txt , by writing one byte at a time
Have a look at this SE question to know more details about advanced Character streams, which are wrappers on top of Byte Streams :
byte stream and character stream
you read from an InputStream and write to an OutputStream.
for example, say you want to copy a file. You would create a FileInputStream to read from the source file and a FileOutputStream to write to the new file.
If your data is a character stream, you could use a FileReader instead of an InputStream and a FileWriter instead of an OutputStream if you prefer.
InputStream input = ... // many different types
OutputStream output = ... // many different types
byte[] buffer = new byte[1024];
int n = 0;
while ((n = input.read(buffer)) != -1)
output.write(buffer, 0, n);
input.close();
output.close();
OutputStream is an abstract class that represents writing output. There are many different OutputStream classes, and they write out to certain things (like the screen, or Files, or byte arrays, or network connections, or etc). InputStream classes access the same things, but they read data in from them.
Here is a good basic example of using FileOutputStream and FileInputStream to write data to a file, then read it back in.
A stream is a continuous flow of liquid, air, or gas.
Java stream is a flow of data from a source into a destination. The source or destination can be a disk, memory, socket, or other programs. The data can be bytes, characters, or objects. The same applies for C# or C++ streams. A good metaphor for Java streams is water flowing from a tap into a bathtub and later into a drainage.
The data represents the static part of the stream; the read and write methods the dynamic part of the stream.
InputStream represents a flow of data from the source, the OutputStream represents a flow of data into the destination.
Finally, InputStream and OutputStream are abstractions over low-level access to data, such as C file pointers.
Stream: In laymen terms stream is data , most generic stream is binary representation of data.
Input Stream : If you are reading data from a file or any other source , stream used is input stream. In a simpler terms input stream acts as a channel to read data.
Output Stream : If you want to read and process data from a source (file etc) you first need to save the data , the mean to store data is output stream .
An output stream is generally related to some data destination like a file or a network etc.In java output stream is a destination where data is eventually written and it ends
import java.io.printstream;
class PPrint {
static PPrintStream oout = new PPrintStream();
}
class PPrintStream {
void print(String str) {
System.out.println(str)
}
}
class outputstreamDemo {
public static void main(String args[]) {
System.out.println("hello world");
System.out.prinln("this is output stream demo");
}
}
For one kind of InputStream, you can think of it as a "representation" of a data source, like a file.
For example:
FileInputStream fileInputStream = new FileInputStream("/path/to/file/abc.txt");
fileInputStream represents the data in this path, which you can use read method to read bytes from the file.
For the other kind of InputStream, they take in another inputStream and do further processing, like decompression.
For example:
GZIPInputStream gzipInputStream = new GZIPInputStream(fileInputStream);
gzipInputStream will treat the fileInputStream as a compressed data source. When you use the read(buffer, 0, buffer.length) method, it will decompress part of the gzip file into the buffer you provide.
The reason why we use InputStream because as the data in the source becomes larger and larger, say we have 500GB data in the source file, we don't want to hold everything in the memory (expensive machine; not friendly for GC allocation), and we want to get some result faster (reading the whole file may take a long time).
The same thing for OutputStream. We can start moving some result to the destination without waiting for the whole thing to finish, plus less memory consumption.
If you want more explanations and examples, you have check these summaries: InputStream, OutputStream, How To Use InputStream, How To Use OutputStream
In continue to the great other answers, in my simple words:
Stream - like mentioned #Sher Mohammad is data.
Input stream - for example is to get input – data – from the file. The case is when I have a file (the user upload a file – input) – and I want to read what we have there.
Output Stream – is the vice versa. For example – you are generating an excel file, and output it to some place.
The “how to write” to the file, is defined at the sender (the excel workbook class) not at the file output stream.
See here example in this context.
try (OutputStream fileOut = new FileOutputStream("xssf-align.xlsx")) {
wb.write(fileOut);
}
wb.close();
I have a file that contains some amount of plain text at the start followed by binary content at the end. The size of the binary content is determined by some one of the plain text lines I read.
I was using a BufferedReader to read the individual lines, however it exposes no methods to refer to read a byte array. The readUTF for a DataInputStream doesnt read all the way to the end of the line, and the readLine method is deprecated.
Using the underlying FileInputStream to read returns empty byte arrays. Any suggestions on how to go about this?
private DOTDataInfo parseFile(InputStream stream) throws IOException{
DOTDataInfo info = new DOTDataInfo();
BufferedReader reader = new BufferedReader(new InputStreamReader(stream));
int binSize = 0;
String line;
while((line = reader.readLine()) != null){
if(line.length() == 0)
break;
DOTProperty prop = parseProperty(line);
info.getProperties().add(prop);
if(prop.getName().equals("ContentSize"))
binSize = Integer.parseInt(prop.getValue());
}
byte[] content = new byte[binSize];
stream.read(content); //Its all empty now. If I use a DataInputStream instead, its got the values from the file
return info;
}
You could use RandomAccessFile. Use readLine() to read the plain text at the start (note the limitations of this, as described in the API), and then readByte() or readFully() to read the subsequent binary data.
Using the underlying FileInputStream
to read returns empty byte arrays.
That's because you have wrapped the stream in a BufferedReader, which has probably consumed all the bytes from the stream when filling up its buffer.
If you genuinely have a file (rather than something harder to seek in, e.g. a network stream) then I suggest something like this:
Open the file as a FileInputStream
Wrap it in InputStreamReader and a BufferedReader
Read the text, so you can find out how much content there is
Close the BufferedReader (which will close the InputStreamReader which will close the FileInputStream)
Reopen the file
Skip to (total file length - binary content length)
Read the rest of the data as normal
You could just call mark() at the start of the FileInputStream and then reset() and skip() to get to the right place if you want to avoid reopening the file. (I was looking for an InputStream.seek() but I can't see one - I can't remember wanting it before in Java, but does it really not have one? Ick.)
You need to use an InputStream. Readers are for character data. Look into wrapping your input stream with a DataInputStream, like:
stream=new DataInputStream(new BufferedInputStream(new FileInputStream(...)));
The data input stream will give you many useful methods to read various types of data, and of course, the base InputStream methods for reading bytes.
(This is actually exactly what a HTTP server must do to read a request with content.)
The readUTF doesn't read a line, it reads a string that was written in (modified) UTF8 format - refer to the JavaDoc.
Alas, DataInputStream is deprecated and does not handle UTF. But this should help (it reads a line from a binary stream, without any lookahead).
public static String lineFrom(InputStream in) throws IOException {
byte[] buf = new byte[128];
int pos = 0;
for (;;) {
int ch = in.read();
if (ch == '\n' || ch < 0) break;
buf[pos++] = (byte) ch;
if (pos == buf.length) buf = Arrays.copyOf(buf, pos + 128);
}
return new String(Arrays.copyOf(buf, pos), "UTF-8");
}
The correct way is to use an InputStream of some form, probably a FileInputStream unless this becomes a performance barrier.
What do you mean "Using the underlying FileInputStream to read returns empty byte arrays."? This seems very unlikely and is probably where your mistake is. Can you show us the example code you've tried?
You can read the text with BufferedReader. When you know where the binary starts you can close the file and open it with RandomAccessFile and read binary from any point in the file.
Or you can read the file as binary and convert to text the sections you identify as text. {Using new String(bytes, encoding)}
I recommend using DataInputStream. You have the following options:
Read both text and binary content with DataInputStream
Open a BufferedReader, read text and close the stream. Then open a DataInputStream, skip bytes equal to the size of the text and read binary data.