Version Comparison in Java

1. Overview

With the advancement of DevOps technologies, it's common to build and deploy an application multiple times in a day.

Therefore, every build is assigned a unique version number so we can distinguish between builds. Sometimes, a need arises to compare the version strings programmatically.

In this article, we'll explore a few ways to compare version strings in Java through various libraries. At last, we'll write a custom program to handle generic version-string comparison.

2. Using maven-artifact

To start with, let's explore how Maven handles version comparison.

2.1. Maven Dependency

First, we'll add the latest maven-artifact Maven dependency to our pom.xml:

<dependency>
    <groupId>org.apache.maven</groupId>
    <artifactId>maven-artifact</artifactId>
    <version>3.6.3</version>
</dependency>

2.2. ComparableVersion

Let's explore the ComparableVersion class. It provides a generic implementation of version comparison with an unlimited number of version components.

It contains a compareTo method, and the result of the comparison will be greater than or less than 0 when one version is greater than or less than the other, respectively:

ComparableVersion version1_1 = new ComparableVersion("1.1");
ComparableVersion version1_2 = new ComparableVersion("1.2");
ComparableVersion version1_3 = new ComparableVersion("1.3");

assertTrue(version1_1.compareTo(version1_2) < 0);
assertTrue(version1_3.compareTo(version1_2) > 0);

Here, we can confirm that the 1.1 version is less than the 1.2 version, and the 1.3 version is greater than the 1.2 version.

However, we will get 0 as a result when comparing the same versions:

ComparableVersion version1_1_0 = new ComparableVersion("1.1.0");
assertEquals(0, version1_1.compareTo(version1_1_0));

2.3. Version Separators and Qualifiers

Additionally, the ComparableVersion class respects the dot (.) and hyphen (-) as separators, where the dot separates major and minor versions, and the hyphen defines qualifiers:

ComparableVersion version1_1_alpha = new ComparableVersion("1.1-alpha");
assertTrue(version1_1.compareTo(version1_1_alpha) > 0);

Here, we can confirm that the 1.1 version is greater than the 1.1-alpha version.

There are a few well-known qualifiers supported by the ComparableVersion like the alpha, beta, milestone, RC, and snapshot (in the order of lowest to highest):

ComparableVersion version1_1_beta = new ComparableVersion("1.1-beta");
ComparableVersion version1_1_milestone = new ComparableVersion("1.1-milestone");
ComparableVersion version1_1_rc = new ComparableVersion("1.1-rc");
ComparableVersion version1_1_snapshot = new ComparableVersion("1.1-snapshot");

assertTrue(version1_1_alpha.compareTo(version1_1_beta) < 0);
assertTrue(version1_1_beta.compareTo(version1_1_milestone) < 0);
assertTrue(version1_1_rc.compareTo(version1_1_snapshot) < 0);
assertTrue(version1_1_snapshot.compareTo(version1_1) < 0);

Also, it allows us to define unknown qualifiers and respects their order, after the already discussed known qualifiers, with case-insensitive lexical order:

ComparableVersion version1_1_c = new ComparableVersion("1.1-c");
ComparableVersion version1_1_z = new ComparableVersion("1.1-z");
ComparableVersion version1_1_1 = new ComparableVersion("1.1.1");
        
assertTrue(version1_1_c.compareTo(version1_1_z) < 0);
assertTrue(version1_1_z.compareTo(version1_1_1) < 0);

3. Using gradle-core

Like Maven, Gradle also has the built-in capability to handle version comparison.

3.1. Maven Dependency

First, let's add the latest gradle-core Maven dependency from the Gradle Releases repo:

<dependency>
    <groupId>org.gradle</groupId>
    <artifactId>gradle-core</artifactId>
    <version>6.1.1</version>
</dependency>

3.2. VersionNumber

The VersionNumber class provided by Gradle compares two versions, similar to Maven's ComparableVersion class:

VersionNumber version1_1 = VersionNumber.parse("1.1");
VersionNumber version1_2 = VersionNumber.parse("1.2");
VersionNumber version1_3 = VersionNumber.parse("1.3");

assertTrue(version1_1.compareTo(version1_2) < 0);
assertTrue(version1_3.compareTo(version1_2) > 0);

VersionNumber version1_1_0 = VersionNumber.parse("1.1.0");
assertEquals(0, version1_1.compareTo(version1_1_0));

3.3. Version Components

Unlike the ComparableVersion class, the VersionNumber class supports only five version components — Major, Minor, Micro, Patch, and Qualifier:

VersionNumber version1_1_1_1_alpha = VersionNumber.parse("1.1.1.1-alpha"); 
assertTrue(version1_1.compareTo(version1_1_1_1_alpha) < 0); 

VersionNumber version1_1_beta = VersionNumber.parse("1.1.0.0-beta"); 
assertTrue(version1_1_beta.compareTo(version1_1_1_1_alpha) < 0);

3.4. Version Schemes

Also, VersionNumber supports a couple of different version schemes like Major.Minor.Micro-Qualifier and Major.Minor.Micro.Patch-Qualifier:

VersionNumber version1_1_1_snapshot = VersionNumber.parse("1.1.1-snapshot");
assertTrue(version1_1_1_1_alpha.compareTo(version1_1_1_snapshot) < 0);

4. Using jackson-core

4.1. Maven Dependency

Similar to other dependencies, let's add the latest jackson-core Maven dependency to our pom.xml:

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.11.1</version>
</dependency>

4.2. Version

Then, we can examine Jackson‘s Version class, which can hold versioning information of a component along with the optional groupId and artifactId values.

Therefore, the constructor of the Version class allows us to define groupId and artifactId, along with components like Major, Minor, and Patch:

public Version (int major, int minor, int patchLevel, String snapshotInfo, String groupId, String artifactId) {
    //...
}

So, let's compare a few versions using the Version class:

Version version1_1 = new Version(1, 1, 0, null, null, null);
Version version1_2 = new Version(1, 2, 0, null, null, null);
Version version1_3 = new Version(1, 3, 0, null, null, null);

assertTrue(version1_1.compareTo(version1_2) < 0);
assertTrue(version1_3.compareTo(version1_2) > 0);

Version version1_1_1 = new Version(1, 1, 1, null, null, null);
assertTrue(version1_1.compareTo(version1_1_1) < 0);

4.3. The snapshotInfo Component

The snapshotInfo component isn't used while comparing two versions:

Version version1_1_snapshot = new Version(1, 1, 0, "snapshot", null, null); 
assertEquals(0, version1_1.compareTo(version1_1_snapshot));

Additionally, the Version class provides the isSnapshot method to check if the version contains a snapshot component:

assertTrue(version1_1_snapshot.isSnapshot());

4.4. The groupId and artifactId Components

Also, this class compares the lexical order of the groupId and artifactId version components:

Version version1_1_maven = new Version(1, 1, 0, null, "org.apache.maven", null);
Version version1_1_gradle = new Version(1, 1, 0, null, "org.gradle", null);
assertTrue(version1_1_maven.compareTo(version1_1_gradle) < 0);

5. Using Semver4J

The Semver4j library allows us to follow the rules of the semantic versioning specification in Java.

5.1. Maven Dependency

First, we'll add the latest semver4j Maven dependency:

<dependency>
    <groupId>com.vdurmont</groupId>
    <artifactId>semver4j</artifactId>
    <version>3.1.0</version>
</dependency>

5.2. Semver

Then, we can use the Semver class to define a version:

Semver version1_1 = new Semver("1.1.0");
Semver version1_2 = new Semver("1.2.0");
Semver version1_3 = new Semver("1.3.0");

assertTrue(version1_1.compareTo(version1_2) < 0);
assertTrue(version1_3.compareTo(version1_2) > 0);

Internally, it parses a version into components like Major, Minor, and Patch.

5.3. Version Comparison

Also, the Semver class comes with various built-in methods like isGreaterThan, isLowerThan, and isEqualTo for version comparison:

Semver version1_1_alpha = new Semver("1.1.0-alpha"); 
assertTrue(version1_1.isGreaterThan(version1_1_alpha)); 

Semver version1_1_beta = new Semver("1.1.0-beta"); 
assertTrue(version1_1_alpha.isLowerThan(version1_1_beta)); 

assertTrue(version1_1.isEqualTo("1.1.0"));

Likewise, it provides the diff method that returns the main difference between the two versions:

assertEquals(VersionDiff.MAJOR, version1_1.diff("2.1.0"));
assertEquals(VersionDiff.MINOR, version1_1.diff("1.2.3"));
assertEquals(VersionDiff.PATCH, version1_1.diff("1.1.1"));

5.4. Version Stability

Also, the Semver class comes with the isStable method to check the stability of a version, determined by the presence or absence of a suffix:

assertTrue(version1_1.isStable());
assertFalse(version1_1_alpha.isStable());

6. Custom Solution

We've seen a few solutions to compare the version strings. If they don't work for a specific use-case, we might have to write a custom solution.

Here's a simple example that works for some basic cases — it can always be extended if we need something more.

The idea here is to tokenize the version strings using a dot delimiter, and then compare integer conversion of every String token, beginning from the left. If the token's integer value is the same, examine the next token, continuing this step until we find a difference (or until we reach the last token in either string):

public static int compareVersions(String version1, String version2) {
    int comparisonResult = 0;
    
    String[] version1Splits = version1.split("\\.");
    String[] version2Splits = version2.split("\\.");
    int maxLengthOfVersionSplits = Math.max(version1Splits.length, version2Splits.length);

    for (int i = 0; i < maxLengthOfVersionSplits; i++){
        Integer v1 = i < version1Splits.length ? Integer.parseInt(version1Splits[i]) : 0;
        Integer v2 = i < version2Splits.length ? Integer.parseInt(version2Splits[i]) : 0;
        int compare = v1.compareTo(v2);
        if (compare != 0) {
            comparisonResult = compare;
            break;
        }
    }
    return comparisonResult;
}

Let's verify our solution by comparing a few versions:

assertTrue(VersionCompare.compareVersions("1.0.1", "1.1.2") < 0);
assertTrue(VersionCompare.compareVersions("1.0.1", "1.10") < 0);
assertTrue(VersionCompare.compareVersions("1.1.2", "1.0.1") > 0);
assertTrue(VersionCompare.compareVersions("1.1.2", "1.2.0") < 0);
assertEquals(0, VersionCompare.compareVersions("1.3.0", "1.3"));

This code has a limitation that it can only compare a version number made of integers delimited by dots.

Therefore, for comparing alphanumeric version strings, we can use a regular expression to segregate alphabets and compare the lexical order.

7. Conclusion

In this article, we looked into various ways to compare version strings in Java.

At first, we examined built-in solutions provided by build frameworks like Maven and Gradle, using the maven-artifact and gradle-core dependencies, respectively. Then, we explored version comparison features of the jackson-core and semver4j libraries.

Last, we wrote a custom solution for generic version string comparison.

As usual, all the code implementations are available over on GitHub.