source: gli/branches/rtl-gli/CheckJavaVersion.java@ 21027

import java.util.regex.Pattern;


public class CheckJavaVersion {
    static final String MINIMUM_VERSION_PREFIX = "1.4";
    
    /**
     * @param args, arg[0] is the minium version of Java required
     * to run the program. arg[1] is the name of the program.
     * If arg[1] is left out, then no distinct program name is
     * mentioned. If arg[0] is left out as well, then Greenstone3's
     * minimum default version of 1.4.x is assumed.
     * The program exits with 1 if the Java version being used is 
     * incompatible and with 2 if it is acceptable.
     */
    public static void main(String[] args) {
        String minimumVersion = MINIMUM_VERSION_PREFIX;
        String programName = "this program"; 
        // the version of java that's in use
        String runningJavaVersion = System.getProperty("java.version");
        
        if(args.length > 0) {
            minimumVersion = args[0];
        }
        if(args.length > 1) {
            programName = args[1];
        }
        
        System.out.println("\nChecking for a compatible Java version..."
                + "\nLooking for minimum version: " + minimumVersion);
        
        // Version numbers can be of the form "1.5.0_2" 
        // We want to split version numbers into the individual numbers
        // For example: splitting 1.5.0_2 will give us {1,5,0,2},
        // while splitting 1.5.0_10 will give us {1,5,0,10}.
        // The comparison then is straightforward.
        
        // We will split version strings into the individual numbers
        // using regular expressions. However, the tokens . and _ are
        // reserved in regular expressions and need to be escaped: 
        // Period: \Q.\E;  underscore: \Q_\E.
        // Once escaped, it should be indicated in the regular expression
        // that the two characters are separate tokens by using |, so 
        // that the regex becomes: ".|_" -> \Q.\E|\Q_\E.
        String period = "\\Q.\\E";
        String underscore = "\\Q_\\E";
             // Can't use Pattern.quote() since it is not there in Java 1.4.*
             //String period = Pattern.quote(".");
             //String underscore = Pattern.quote("_");
        
        String[] minVersionNums = minimumVersion.split(period+"|"+underscore);
        String[] runningVersionNums =runningJavaVersion.split(period+"|"+underscore);
        
        boolean acceptable = true;
        // only keep looping while we haven't gone past the end of either array
        int i=0;
        for(; i < minVersionNums.length && i < runningVersionNums.length; i++)
        {
            int min = Integer.parseInt(minVersionNums[i]);
            int run = Integer.parseInt(runningVersionNums[i]);
            if(run > min) { 
                    // certain success: one of the higher positional numbers 
                    // of the running version is greater than the corresponding
                    // number of the minimum version, meaning we've finished.
                break;
            } else if(run < min) { 
                // fail: running version number is lower than corresponding 
                // minimum version number
                acceptable = false;
                break;
            } 
        }
        
        // Consider minVersion = 1.5.0_10 and runningVersion = 1.5.0
        // this means the runningversion is still insufficient. 
        // HOWEVER, minVersion being longer does not always mean it is
        // a later version, consider: min=1.5.0_9.12 and run=1.5.0_10
        // This should be acceptable since 10 > 9 even though min is longer.
        // SOLUTION: If the last values for both were the same, the running 
        // Version is not compatible if the minVersionNums array is longer
        int min = Integer.parseInt(minVersionNums[i-1]);
        int run = Integer.parseInt(runningVersionNums[i-1]);
        
        // if the last values were the same, check whether min is longer
        // in which case the running version is not acceptable
        if(min == run && minVersionNums.length > runningVersionNums.length) 
        {
            acceptable = false;
        }
        
        if(acceptable) {
            System.out.println("Found compatible Java version " +runningJavaVersion);
            System.exit(2); // acceptable case
        } else {
            System.out.println("The current Java version " + 
                runningJavaVersion + " is insufficient to run " + programName);
            System.exit(1);
        } 
    }
}