Java Streams Overview, Part I

For a long time, I had a gap in my knowledge of Java streams. On a basic level, I could use them, but I did not a deep understanding of them. So, I decided to do a quick overview of Java streams.

In this article, I will deal with many everything from the fundamentals to chaining and clean-up.

Hope this helps you broaden your knowledge of Java streams. 

What Are Streams?

A stream is an ordered sequence of data that...

• Provides a common I/O model
• Abstracts details from an underlying source or destination

Whether you use streams to take data from memory, storage, or your network, it will hide the implementation details from you. The details are abstracted away, so in every situation, you can look at it as an ordered sequence of data.

• Stream types are uni-directional

This means that if you create an instance of a Java stream, you decide whether you would like to write to it or read from it. You can’t do both at the given time on a single stream.

We can divide the streams into two categories:

• Byte streams – Interacts as binary data
• Text streams – Interacts as unicode characters

The general interaction is the same for both Java stream types

Reading With Streams

As we mentioned, each stream is used either to read from or write to.

Firstly, let us see how we can read data from Java streams.

The base class to read binary data in Java is the InputStream. And the base class to read text data is called the Readerclass.

Both classes almost have the same two methods:

•  int read()
  
•  int read(byte/char[] buff)
  

Notice that in both scenarios, they give back an Integer value. These are interpreted values. An integer is a 32-bit container, so it will work in both cases.

The difference between the two:

• The InputStream works with bytes, which are 8-bits.
• The Reader works with unicode characters, which are 16-bits.

Read Bytes With InputStream

InputStream input = // create input stream
int result;

while(result = input.read() >= 0) //Indicates the end-of-stream with a return value of -1
byte byteVal = (byte)result;
// do something with byteVal
};

Read Text with Reader

Reader reader = // create reader
int result;

while(result = reader.read() >= 0)//Indicates the end-of-stream with a return value of -1
char charVal = (char)result;
// do something with charVal
};

Note that if you would like to retrieve the value, you simply need to cast the result to the appropriate type — in this case, byte or char.

Writing With Streams

To write data, there are two base classes similar to the read streams.

•  OutputStream (for bytes)
•  Writer (for text)

Writing Bytes With OutputStream

To write with OutputStream, you can pass a single byte the write method, or you can pass a byte array as well.

OutputStream output // create output stream;
Byte byteVal = 100;

output.write(byteVal);

byte[] byteBuff = {0, 10, 20};
output.write(byteBuff);

Writing Characters With Writer

To write with the Writer class, you can pass a simple character, character array, or String to its  write method.

Writer writer // create output stream;
char charVal = 'c';

writer.write(charVal);

char[] charArray = {'c', 'h', 'a', 'r'};
writer.write(charArray);

String stringVal = "String";
writer.write(stringVal);

As you can see, you need much less code to write than to read.

Common Java Stream Classes

Above, I wrote about the base stream classes. Now, let us go a bit deeper and talk about the different implementations.

Common Input/OutputStream Derived Classes

•  ByteArrayInputStream /  ByteArrayOutputStream – Enables us to create a stream over a byte array
•  PipedInputStream / PipedOutputStream – This is much like a producer-consumer concept. A piped output stream can be connected to a piped input stream to create a communications pipe. The piped output stream is the sending end of the pipe. Typically, data is written to a PipedOutputStream object by one thread and data is read from the connected PipedInputStream by some other thread.
•  FileInputStream /  FileOutputStream – These allow us to create streams over files.

Common Reader/Writer Derived Classes

•  CharArrayReader / Writer – Allows creating streams over characters
•  StringReader / Writer – Allows creating stream over Strings
•  PipedReader / Writer – Allows creating a stream in a Producer/Consumer relationship over text. Similarly to the PipedOutput / InputStream 
•  InputStreamReader / Writer – Allows us to create a stream over an Input / OutputStream 
•  FileReader / Writer – These are delivered from the least mentioned above. It allows us to make a stream over text files.

Stream Errors and Clean-Up

So far, we looked at the general features of streams, but we have not considered all the realities of working with them.

Stream Realities

Let us see the two main groups here. 

Clean-Up

Problems

• Streams are backed by physical storage, which often exists outside the Java runtime, like files or network connections.
• Hence, Java may not reliably clean up, so we need to do our own reliable clean-up. We need to close the Streams when we are done with them.

Solutions

• Streams implement the Closeable interface, which implements one single close method. So, this is our responsibility to call it.

Let us see a simple solution:

Reader reader; 
try{
reader = // create output stream;
// do something with reader;
}catch (IOException e) {
//handle exception
}finally {
if(reader != null)
reader.close();
}

The problem with the above example is that you always need to implement it. Usually, we use Streams frequently, so it should be done automatically. Let us see how we can achieve it.

Automating Clean-Up

•  AutoClosable interface
  • One method: close
  • The base interface of the Closable interface, so every Stream supports it.
  • Provides support for try-with-resources

Try-With-Resources

• Automates the clean-up of one or more resources
  • A “resource” is any type that implements  AutoClosable
• Syntax similar to traditional try statement
• Optionally includes catch block(s)
  • Handle try body
  • Handle close method call

Working With Try-With-Resources

Here, I provided a simple example of how we can use the automatic close of streams with try-with-resources block.

I will use it through a FileInputStream. We will talk about this specific stream later.

 try(FileInputStream input = new FileInputStream("file1.txt")) {

        int data = input.read();
        while(data != -1){
            System.out.print((char) data);
            data = input.read();
        }
    }

With the above approach, you do not need to investigate further work to close your streams.

Summary

In this article, we talked about the fundamentals of Java streams, what are they, how they work, and how you can use them. In my next article, I will dig a bit deeper, and I will write about more advanced Stream topics like chaining, buffered streams, and how to use file systems with it. So stay tuned!

See more about streams in the official Java documentation here.

If you enjoyed this article and want to learn more about Java Streams, check out this collection of tutorials and articles on all things Java Streams.