Why we use inputstream

See Also: read byte[], int, int read public int read byte[] b, int off, int len throws IOException Reads up to len bytes of data from the input stream into an array of bytes. An attempt is made to read as many as len bytes, but a smaller number may be read. If len is zero, then no bytes are read and 0 is returned; otherwise, there is an attempt to read at least one byte.

If no byte is available because the stream is at end of file, the value -1 is returned; otherwise, at least one byte is read and stored into b. The number of bytes read is, at most, equal to len. The read b, off, len method for class InputStream simply calls the method read repeatedly. If the first such call results in an IOException , that exception is returned from the call to the read b, off, len method.

If any subsequent call to read results in a IOException , the exception is caught and treated as if it were end of file; the bytes read up to that point are stored into b and the number of bytes read before the exception occurred is returned.

The default implementation of this method blocks until the requested amount of input data len has been read, end of file is detected, or an exception is thrown. Subclasses are encouraged to provide a more efficient implementation of this method. Parameters: b - the buffer into which the data is read. NullPointerException - If b is null. The skip method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly 0. This may result from any of a number of conditions; reaching end of file before n bytes have been skipped is only one possibility.

The actual number of bytes skipped is returned. If n is negative, no bytes are skipped. The skip method of this class creates a byte array and then repeatedly reads into it until n bytes have been read or the end of the stream has been reached. For instance, the implementation may depend on the ability to seek. Parameters: n - the number of bytes to be skipped.

Returns: the actual number of bytes skipped. The next invocation might be the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes. Note that while some implementations of InputStream will return the total number of bytes in the stream, many will not. It is never correct to use the return value of this method to allocate a buffer intended to hold all data in this stream.

A subclass' implementation of this method may choose to throw an IOException if this input stream has been closed by invoking the close method. The available method for class InputStream always returns 0. Program to read from a file using BufferedReader class. Program to write to a File using FileWriter class. Getting wrong output in fetching data? React button component not visible on output screen , But showing in inspect mode React testing library difference between snapshot and debug output How to do file streaming on Java to the browser without letting the user save the file?

Related Questions. Why are instance variables in Java always private? Stopping a Thread in Java? Java : in what order are static final fields initialized? Is java. Hashtable thread safe? 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.

For one kind of InputStream, you can think of it as a "representation" of a data source, like a file. For example:. For the other kind of InputStream, they take in another inputStream and do further processing, like decompression. When you use the read buffer, 0, buffer. The reason why we use InputStream because as the data in the source becomes larger and larger, say we have GB 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. 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. See here example in this context. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Why and when do we use them? Ask Question. Asked 11 years, 11 months ago. Active 4 months ago. Viewed k times. Someone explain to me what InputStream and OutputStream are? Improve this question.

Bohemian Bohemian 5, 11 11 gold badges 37 37 silver badges 47 47 bronze badges. Add a comment. Active Oldest Votes. InputStream is used for many things that you read from. OutputStream is used for many things that you write to. Improve this answer.