Add deprecation warnings for JAVA_HOME/older versions of Java (#13358)

* Add deprecation warnings for JAVA_HOME/older versions of Java

Logstash 8.0 will remove support for java versions before java 11, this commit
adds entries to the deprecation log warning against this.
Also adds use of `JAVA_HOME` to the deprecation log.

logstash-core/lib/logstash/runner.rb

@@ -14,7 +14,7 @@
 # KIND, either express or implied.  See the License for the
 # specific language governing permissions and limitations
 # under the License.
-
+java_import 'org.logstash.util.JavaVersion'
 Thread.abort_on_exception = true
 Encoding.default_external = Encoding::UTF_8
 $DEBUGLIST = (ENV["DEBUG"] || "").split(",")
@@ -326,6 +326,12 @@ class LogStash::Runner < Clamp::StrictCommand
       deprecation_logger.deprecated msg
     end
 
+    if JavaVersion::CURRENT < JavaVersion::JAVA_11
+        deprecation_logger.deprecated I18n.t("logstash.runner.java.version",
+                                             :java_home => java.lang.System.getProperty("java.home"))
+    end
+
+    deprecation_logger.deprecated I18n.t("logstash.runner.java.home") if ENV["JAVA_HOME"]
     # Skip any validation and just return the version
     if version?
       show_version

logstash-core/locales/en.yml

@@ -433,6 +433,18 @@ en:
         quiet: |+
           Set the log level to info.
           DEPRECATED: use --log.level=info instead.
+      java:
+        home: >-
+          The use of JAVA_HOME has been deprecated. Logstash 8.0 and later ignores JAVA_HOME and uses the bundled JDK.
+          Running Logstash with the bundled JDK is recommended.
+          The bundled JDK has been verified to work with each specific version of Logstash, and generally provides best performance and reliability.
+          If you have compelling reasons for using your own JDK (organizational-specific compliance requirements, for example), you can configure LS_JAVA_HOME to use that version instead.
+        version: >-
+          Starting from Logstash 8.0, the minimum required version of Java is Java 11; your Java version from
+          %{java_home} does not meet this requirement. Please reconfigure your version of Java to one that is supported.
+          Running Logstash with the bundled JDK is recommended.
+          The bundled JDK has been verified to work with each specific version of Logstash, and generally provides best performance and reliability.
+          If you have compelling reasons for using your own JDK (organizational-specific compliance requirements, for example), you can configure LS_JAVA_HOME to use that version instead.
     settings:
       deprecation:
         set: >-

logstash-core/src/main/java/org/logstash/util/JavaVersion.java

@@ -0,0 +1,84 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *	http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.logstash.util;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+
+/**
+ * Helper class to compare current version of JVM with a target version.
+ * Based on JavaVersion class from elasticsearch java version checker tool
+ */
+public class JavaVersion implements Comparable<JavaVersion> {
+
+    public static final JavaVersion CURRENT = parse(System.getProperty("java.specification.version"));
+    public static final JavaVersion JAVA_11 = parse("11");
+    private final List<Integer> version;
+
+    private JavaVersion(List<Integer> version){
+        this.version = version;
+    }
+
+    static JavaVersion parse(final String value) {
+        if (value.matches("^0*[0-9]+(\\.[0-9]+)*$") == false) {
+            throw new IllegalArgumentException(value);
+        }
+
+        final List<Integer> version = new ArrayList<Integer>();
+        final String[] components = value.split("\\.");
+        for (final String component : components) {
+            version.add(Integer.valueOf(component));
+        }
+        return new JavaVersion(version);
+    }
+
+    public static int majorVersion(final JavaVersion javaVersion) {
+        Objects.requireNonNull(javaVersion);
+        if (javaVersion.version.get(0) > 1) {
+            return javaVersion.version.get(0);
+        } else {
+            return javaVersion.version.get(1);
+        }
+    }
+
+    private static int compare(final JavaVersion leftVersion, final JavaVersion rightVersion) {
+        List<Integer> left = leftVersion.version;
+        List<Integer> right = rightVersion.version;
+        // lexicographically compare two lists, treating missing entries as zeros
+        final int len = Math.max(left.size(), right.size());
+        for (int i = 0; i < len; i++) {
+            final int l = (i < left.size()) ? left.get(i) : 0;
+            final int r = (i < right.size()) ? right.get(i) : 0;
+            if (l < r) {
+                return -1;
+            }
+            if (r < l) {
+                return 1;
+            }
+        }
+        return 0;
+    }
+
+    @Override
+    public int compareTo(JavaVersion other) {
+        return compare(this, other);
+    }
+}