1 | import java.util.regex.Pattern;
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2 |
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3 |
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4 | public class CheckJavaVersion {
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5 | static final String MINIMUM_VERSION_PREFIX = "1.4";
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6 |
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7 | /**
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8 | * @param args, arg[0] is the minium version of Java required
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9 | * to run the program. arg[1] is the name of the program.
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10 | * If arg[1] is left out, then no distinct program name is
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11 | * mentioned. If arg[0] is left out as well, then Greenstone3's
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12 | * minimum default version of 1.4.x is assumed.
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13 | * The program exits with -1 if the Java version being used is
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14 | * incompatible and with 0 if it is acceptable.
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15 | */
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16 | public static void main(String[] args) {
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17 | String minimumVersion = MINIMUM_VERSION_PREFIX;
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18 | String programName = "this program";
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19 | // the version of java that's in use
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20 | String runningJavaVersion = System.getProperty("java.version");
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21 |
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22 | if(args.length > 0) {
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23 | minimumVersion = args[0];
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24 | }
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25 | if(args.length > 1) {
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26 | programName = args[1];
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27 | }
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28 |
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29 | System.out.println("\nChecking for a compatible Java version..."
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30 | + "\nLooking for minimum version: " + minimumVersion);
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31 |
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32 | // Version numbers can be of the form "1.5.0_2"
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33 | // We want to split version numbers into the individual numbers
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34 | // For example: splitting 1.5.0_2 will give us {1,5,0,2},
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35 | // while splitting 1.5.0_10 will give us {1,5,0,10}.
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36 | // The comparison then is straightforward.
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37 |
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38 | // We will split version strings into the individual numbers
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39 | // using regular expressions. However, the tokens . and _ are
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40 | // reserved in regular expressions and need to be escaped:
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41 | // Period: \Q.\E; underscore: \Q_\E.
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42 | // Once escaped, it should be indicated in the regular expression
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43 | // that the two characters are separate tokens by using |, so
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44 | // that the regex becomes: ".|_" -> \Q.\E|\Q_\E.
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45 | String period = Pattern.quote(".");
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46 | String underscore = Pattern.quote("_");
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47 |
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48 | String[] minVersionNums = minimumVersion.split(period+"|"+underscore);
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49 | String[] runningVersionNums =runningJavaVersion.split(period+"|"+underscore);
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50 |
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51 | boolean acceptable = true;
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52 | // only keep looping while we haven't gone past the end of either array
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53 | for(int i=0; i < minVersionNums.length && i < runningVersionNums.length; i++)
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54 | {
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55 | int min = Integer.parseInt(minVersionNums[i]);
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56 | int run = Integer.parseInt(runningVersionNums[i]);
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57 | if(run < min) {
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58 | // fail: running version number is lower than corresponding
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59 | // minimum version number
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60 | acceptable = false;
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61 | break;
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62 | }
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63 | }
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64 |
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65 | if(acceptable) {
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66 | System.out.println("Found compatible Java version " +runningJavaVersion);
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67 | System.exit(0); // acceptable case
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68 | } else {
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69 | System.out.println("The current Java version " +
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70 | runningJavaVersion + " is insufficient to run " + programName);
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71 | System.exit(-1);
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72 | }
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73 | }
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74 | } |
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