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About Mary Zheng

Mary Zheng
Mary has graduated from Mechanical Engineering department at ShangHai JiaoTong University. She also holds a Master degree in Computer Science from Webster University. During her studies she has been involved with a large number of projects ranging from programming and software engineering. She works as a senior Software Engineer in the telecommunications sector where she acts as a leader and works with others to design, implement, and monitor the software solution.

Java Convert Byte[] array to String Example

1. Introduction

A byte array is an array of bytes. A byte is binary data with 8 bits which represents an integer with values from -128 to 127. A char is a primitive data type which represents a character. The bytes translate to characters based on the character encoding scheme (such as Unicode, UTF-8, UTF-16, and UTF-32). The String class represents character strings. Therefore, we can convert a byte array into a String object based on a character encoding scheme.

Java String class provides several constructors to convert a byte[] into a String. Here is the syntax:

 String​(byte[] bytes)    
String​(byte[] bytes, int offset, int length)    
String​(byte[] bytes, int offset, int length, String charsetName)    
String​(byte[] bytes, int offset, int length, Charset charset)    
String​(byte[] bytes, String charsetName)    
String​(byte[] bytes, Charset charset)

In this example, I will create a Junit test class to demonstrate how to convert a byte[] into a String using these constructors.

2. Technologies Used

The example code in this article was built and run using:

  • Java 1.8.101
  • Eclipse Oxygen
  • Junit
  • Maven 3.3.9

3. Maven Project

3.1 Dependency

Add Junit to the pom.xml.

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>
	<groupId>java-bytearray</groupId>
	<artifactId>java-bytearray</artifactId>
	<version>0.0.1-SNAPSHOT</version>

	<properties>
		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
	</properties>

	<build>
		<sourceDirectory>src</sourceDirectory>
		<plugins>
			<plugin>
				<artifactId>maven-compiler-plugin</artifactId>
				<version>3.8.0</version>
				<configuration>
					<release>11</release>
				</configuration>
			</plugin>
		</plugins>
	</build>

	<dependencies>
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>4.12</version>
			<scope>test</scope>
		</dependency>
	</dependencies>

</project>

3.2 Construct String from Byte[]

In this step, I will create a ByteArraytoStringTest class which constructs a String from a byte[] with a different character encoding scheme. It defines two constants:

  • TEST_BYTES_ARR – a byte[] with four elements: {77, 97, 114, 121}. These bytes translate to Mary in UTF-8, ISO-8859-1, and ASCII; to 慍祲 in UTF-16LE; and to 䵡特 in UTF-16 and UTF-16BE.
  • MARY – a String with value of “Mary”.

It includes test methods to convert the TEST_BYTES_ARR into a String object based on the Ascii, utf-8, utf-16, utf-32, and iso_8859-1.

ByteArraytoStringTest.java

package org.jcg.zheng;

import static org.junit.Assert.assertEquals;

import java.nio.charset.StandardCharsets;
import java.util.Arrays;

import org.junit.Test;

public class ByteArrayToStringTest {

    private static final String MARY = "Mary";
    private byte[] TEST_BYTES_ARR = new byte[] { 77, 97, 114, 121 };

    @Test
    public void test_default() {
        String newString = new String(TEST_BYTES_ARR);
        assertEquals(MARY, newString);
    }

    @Test
    public void test_utf8() {
        String newString = new String(TEST_BYTES_ARR, StandardCharsets.UTF_8);
        assertEquals(MARY, newString);
    }

    @Test
    public void test_ascii() {
        String newString = new String(TEST_BYTES_ARR, StandardCharsets.US_ASCII);
        assertEquals(MARY, newString);
    }

    @Test
    public void test_iso_8859() {
        String stringTextOfByteArray = new String(TEST_BYTES_ARR, StandardCharsets.ISO_8859_1);
        assertEquals(MARY, stringTextOfByteArray);
    }

    @Test
    public void test_utf_16() {
        String stringTextOfByteArray = new String(TEST_BYTES_ARR, StandardCharsets.UTF_16);
        assertEquals("䵡特", stringTextOfByteArray);
    }

    @Test
    public void test_utf16Be() {
        String newString = new String(TEST_BYTES_ARR, StandardCharsets.UTF_16BE);
        assertEquals("䵡特", newString);
    }

    @Test
    public void test_utf16Le() {
        String newString = new String(TEST_BYTES_ARR, StandardCharsets.UTF_16LE);
        assertEquals("慍祲", newString);
    }

    @Test
    public void toStringFormat() {
        String stringRepresntationOfByteArray = Arrays.toString(TEST_BYTES_ARR);
        assertEquals("[77, 97, 114, 121]", stringRepresntationOfByteArray);
    }
}

Note: The string representation of a byte array at line 59 is different from the string constructed from a byte[]. The string constructed with the same byte array would be different based on a different character encoding scheme.

4. Demo

I will execute the Junit tests and capture the results.

Convert Byte[] array to String - Junit Test Results
Figure 1 Junit Test Results

5. Java Convert byte[] array to String – Summary

In this example, we demonstrated how to convert a byte[] to String with java.lang.String constructors.

I also demonstrated that Arrays.toString returns a String representation of the byte array, which is different from converting a byte[] into a String object.

6. Download the Source Code

This example consists of a Maven project to convert a byte[] into a String object.

Download
You can download the full source code of this example here: Java Convert Byte[] to String Example
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