1 /* 2 * Copyright (C) 2017 The Gson authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.google.gson.internal; 18 19 /** 20 * Utility to check the major Java version of the current JVM. 21 */ 22 public final class JavaVersion { 23 // Oracle defines naming conventions at http://www.oracle.com/technetwork/java/javase/versioning-naming-139433.html 24 // However, many alternate implementations differ. For example, Debian used 9-debian as the version string 25 26 private static final int majorJavaVersion = determineMajorJavaVersion(); 27 determineMajorJavaVersion()28 private static int determineMajorJavaVersion() { 29 String javaVersion = System.getProperty("java.version"); 30 return getMajorJavaVersion(javaVersion); 31 } 32 33 // Visible for testing only getMajorJavaVersion(String javaVersion)34 static int getMajorJavaVersion(String javaVersion) { 35 int version = parseDotted(javaVersion); 36 if (version == -1) { 37 version = extractBeginningInt(javaVersion); 38 } 39 if (version == -1) { 40 return 6; // Choose minimum supported JDK version as default 41 } 42 return version; 43 } 44 45 // Parses both legacy 1.8 style and newer 9.0.4 style parseDotted(String javaVersion)46 private static int parseDotted(String javaVersion) { 47 try { 48 String[] parts = javaVersion.split("[._]"); 49 int firstVer = Integer.parseInt(parts[0]); 50 if (firstVer == 1 && parts.length > 1) { 51 return Integer.parseInt(parts[1]); 52 } else { 53 return firstVer; 54 } 55 } catch (NumberFormatException e) { 56 return -1; 57 } 58 } 59 extractBeginningInt(String javaVersion)60 private static int extractBeginningInt(String javaVersion) { 61 try { 62 StringBuilder num = new StringBuilder(); 63 for (int i = 0; i < javaVersion.length(); ++i) { 64 char c = javaVersion.charAt(i); 65 if (Character.isDigit(c)) { 66 num.append(c); 67 } else { 68 break; 69 } 70 } 71 return Integer.parseInt(num.toString()); 72 } catch (NumberFormatException e) { 73 return -1; 74 } 75 } 76 77 /** 78 * @return the major Java version, i.e. '8' for Java 1.8, '9' for Java 9 etc. 79 */ getMajorJavaVersion()80 public static int getMajorJavaVersion() { 81 return majorJavaVersion; 82 } 83 84 /** 85 * @return {@code true} if the application is running on Java 9 or later; and {@code false} otherwise. 86 */ isJava9OrLater()87 public static boolean isJava9OrLater() { 88 return majorJavaVersion >= 9; 89 } 90 JavaVersion()91 private JavaVersion() { } 92 } 93