1. Overview

When dealing with Strings in Java, we sometimes need to encode them into a specific charset.

This tutorial is a practical guide showing different ways to encode a String to the UTF-8 charset.

For a more technical deep-dive, see our Guide to Character Encoding.

2. Defining the Problem

To showcase the Java encoding, we’ll work with the German String “Entwickeln Sie mit Vergnügen”:

String germanString = "Entwickeln Sie mit Vergnügen";
byte[] germanBytes = germanString.getBytes();

String asciiEncodedString = new String(germanBytes, StandardCharsets.US_ASCII);

assertNotEquals(asciiEncodedString, germanString);

This String encoded using US_ASCII gives us the value “Entwickeln Sie mit Vergn?gen” when printed because it doesn’t understand the non-ASCII ü character.

But when we convert an ASCII-encoded String that uses all English characters to UTF-8, we get the same string:

String englishString = "Develop with pleasure";
byte[] englishBytes = englishString.getBytes();

String asciiEncondedEnglishString = new String(englishBytes, StandardCharsets.US_ASCII);

assertEquals(asciiEncondedEnglishString, englishString);

Let’s see what happens when we use the UTF-8 encoding.

3. Encoding With Core Java

Let’s start with the core library.

Strings are immutable in Java, which means we cannot change a String character encoding. To achieve what we want, we need to copy the bytes of the String and then create a new one with the desired encoding.

First, we get the String bytes, and then we create a new one using the retrieved bytes and the desired charset:

String rawString = "Entwickeln Sie mit Vergnügen";
byte[] bytes = rawString.getBytes(StandardCharsets.UTF_8);

String utf8EncodedString = new String(bytes, StandardCharsets.UTF_8);

assertEquals(rawString, utf8EncodedString);

4. Encoding With Java 7 StandardCharsets

Alternatively, we can use the StandardCharsets class introduced in Java 7 to encode the String.

First, we’ll encode the String into bytes, and second, we’ll decode it into a UTF-8 String:

String rawString = "Entwickeln Sie mit Vergnügen";
ByteBuffer buffer = StandardCharsets.UTF_8.encode(rawString); 

String utf8EncodedString = StandardCharsets.UTF_8.decode(buffer).toString();

assertEquals(rawString, utf8EncodedString);

5. Encoding With Commons-Codec

Besides using core Java, we can alternatively use Apache Commons Codec to achieve the same results.

Apache Commons Codec is a handy package containing simple encoders and decoders for various formats.

First, let’s start with the project configuration.

When using Maven, we have to add the commons-codec dependency to our pom.xml:

<dependency>
 <groupId>commons-codec</groupId>
 <artifactId>commons-codec</artifactId>
 <version>1.14</version>
</dependency>

Then, in our case, the most interesting class is StringUtils, which provides methods to encode Strings.

Using this class, getting a UTF-8 encoded String is pretty straightforward:

String rawString = "Entwickeln Sie mit Vergnügen"; 
byte[] bytes = StringUtils.getBytesUtf8(rawString);
 
String utf8EncodedString = StringUtils.newStringUtf8(bytes);

assertEquals(rawString, utf8EncodedString);

6. Conclusion

Encoding a String into UTF-8 isn’t difficult, but it’s not that intuitive. This article presents three ways of doing it, using either core Java or Apache Commons Codec.