Convert an Input Stream to a String in Java

This post will discuss how to convert an input stream to a string in Java.

There are several ways to convert an input stream to a string in Java, depending on the version of Java we are using and the libraries we have available. Here are some of the most common methods:

1. Using `BufferedReader` class

This is a low-level approach that reads bytes from the input character stream and decodes them into characters using a specified charset. The idea is to use the efficient BufferedReader class to read text from the InputStream by wrapping a BufferedReader around InputStreamReader. The characters are then appended to a StringBuilder object, which can be converted to a String. Here’s an example of this approach:

import java.io.*;

import java.nio.charset.StandardCharsets;

class Main

{

public static String getString(InputStream in) throws IOException

{

Reader reader = new InputStreamReader(in, StandardCharsets.UTF_8);

BufferedReader br = new BufferedReader(reader);

StringBuilder sb = new StringBuilder();

String line;

while ((line = br.readLine()) != null) {

sb.append(line).append('\n');

}

br.close();

return sb.toString();

}

public static void main(String[] args) throws IOException

{

byte[] bytes = "Techie Delight".getBytes(StandardCharsets.UTF_8);

InputStream in = new ByteArrayInputStream(bytes);

System.out.println(getString(in)); // Techie Delight

in.close();

}

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We can also use the Java 8 Stream API to process the input stream. The idea is to can use the lines() method of BufferedReader to read each line from the InputStream as a Stream, and then use the Collectors.joining() method to join them into a single String. Here’s an example of how we can achieve this:

import java.io.*;

import java.nio.charset.StandardCharsets;

import java.util.stream.Collectors;

class Main

{

public static String getString(InputStream in) {

return new BufferedReader(new InputStreamReader(in, StandardCharsets.UTF_8))

.lines()

.collect(Collectors.joining("\n"));

}

public static void main(String[] args) throws IOException

{

byte[] bytes = "Techie Delight".getBytes(StandardCharsets.UTF_8);

InputStream in = new ByteArrayInputStream(bytes);

System.out.println(getString(in)); // Techie Delight

in.close();

}

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2. Using `Scanner` class

The Scanner class can scan text from various sources, including InputStreams. We can use a delimiter to specify how to split the input into tokens, and then use the next() method to get the next token as a String. The default delimiter is whitespace, but we can change it to any regular expression. We can use the beginning of the input or the end of the input as a delimiter. To illustrate, consider the following example:

import java.io.ByteArrayInputStream;

import java.io.IOException;

import java.io.InputStream;

import java.nio.charset.StandardCharsets;

import java.util.Scanner;

class Main

{

public static String getString(InputStream in) throws IOException

{

return new Scanner(in, StandardCharsets.UTF_8.toString())

.useDelimiter("\\z") // `\z` represents the end of the input

.next();

}

public static void main(String[] args) throws IOException

{

byte[] bytes = "Techie Delight".getBytes(StandardCharsets.UTF_8);

InputStream in = new ByteArrayInputStream(bytes);

System.out.println(getString(in)); // Techie Delight

in.close();

}

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3. Using Guava Library

Another option is to use the third party libraries that provide utility methods to convert an InputStream to a String, such as Google Guava. The CharStreams class by Guava provides the toString() method that can read all characters from a Readable object and returns them as a String. The idea is to get a Readable object from the input stream, so can convert it to string. We can do so by wrapping an InputStream with an InputStreamReader. Here is the code demonstrating this:

import com.google.common.io.CharStreams;

import java.io.*;

import java.nio.charset.StandardCharsets;

class Main

{

public static String getString(InputStream in) throws IOException

{

InputStreamReader isr = new InputStreamReader(in, StandardCharsets.UTF_8.toString());

return CharStreams.toString(isr);

}

public static void main(String[] args) throws IOException

{

byte[] bytes = "Techie Delight".getBytes(StandardCharsets.UTF_8);

InputStream in = new ByteArrayInputStream(bytes);

System.out.println(getString(in)); // Techie Delight

in.close();

}

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4. Using Apache Commons IO

Like Guava, IOUtils class by Apache Commons IO provides the toString() method which can directly get the contents of an InputStream as a string using the specified character encoding. We can also use the IOUtils.copy() method that copies bytes from an InputStream to chars on a Writer using the specified character encoding. These methods offers better performance and error handling than the plain Java methods. Here is an example of using these methods:

import org.apache.commons.io.IOUtils;

import java.io.*;

import java.nio.charset.StandardCharsets;

class Main

{

public static String getString1(InputStream in) throws IOException {

return IOUtils.toString(in, StandardCharsets.UTF_8.toString());

}

public static String getString2(InputStream in) throws IOException {

Writer writer = new StringWriter();

IOUtils.copy(in, writer, StandardCharsets.UTF_8.toString());

return writer.toString();

}

public static void main(String[] args) throws IOException

{

byte[] bytes = "Techie Delight".getBytes(StandardCharsets.UTF_8);

InputStream in = new ByteArrayInputStream(bytes);

System.out.println(getString1(in)); // Techie Delight

in.close();

in = new ByteArrayInputStream(bytes);

System.out.println(getString2(in)); // Techie Delight

in.close();

}

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That’s all about converting an input stream to a string in Java.

Convert an Input Stream to a String in Java

1. Using BufferedReader class

2. Using Scanner class

3. Using Guava Library

4. Using Apache Commons IO

1. Using `BufferedReader` class

2. Using `Scanner` class