jvm - Getting Java version at runtime

Question

I need to work around a Java bug in JDK 1.5 which was fixed in 1.6. I'm using the following condition:

if (System.getProperty("java.version").startsWith("1.5.")) {
    ...
} else {
    ...
}

Will this work for other JVMs? Is there a better way to check this?

Answer 1

java.version is a system property that exists in every JVM. There are two possible formats for it:

• Java 8 or lower: 1.6.0_23, 1.7.0, 1.7.0_80, 1.8.0_211
• Java 9 or higher: 9.0.1, 11.0.4, 12, 12.0.1

Here is a trick to extract the major version: If it is a 1.x.y_z version string, extract the character at index 2 of the string. If it is a x.y.z version string, cut the string to its first dot character, if one exists.

private static int getVersion() {
    String version = System.getProperty("java.version");
    if(version.startsWith("1.")) {
        version = version.substring(2, 3);
    } else {
        int dot = version.indexOf(".");
        if(dot != -1) { version = version.substring(0, dot); }
    } return Integer.parseInt(version);
}

Now you can check the version much more comfortably:

if(getVersion() < 6) {
    // ...
}