Fix old MDC java version parsing bug.

Author: lsimons

src/main/java/org/apache/log4j/MDC.java

@@ -72,9 +72,7 @@ public class MDC {
 
     private MDC() {
         java1 = Loader.isJava1();
-        if (!java1) {
-            tlm = new ThreadLocalMap();
-        }
+        tlm = new ThreadLocalMap();
 
         try {
             removeMethod = ThreadLocal.class.getMethod("remove", null);

src/main/java/org/apache/log4j/helpers/Loader.java

@@ -33,22 +33,12 @@ public class Loader  {
 
   static final String TSTR = "Caught Exception while in Loader.getResource. This may be innocuous.";
 
-  // We conservatively assume that we are running under Java 1.x
-  static private boolean java1 = true;
+  // We are on java 1.2+ since we compile with source/target >1.4
+  static private final boolean java1 = false;
 
   static private boolean ignoreTCL = false;
 
   static {
-    String prop = OptionConverter.getSystemProperty("java.version", null);
-    
-    if(prop != null) {
-      int i = prop.indexOf('.');
-      if(i != -1) {	
-	if(prop.charAt(i+1) != '1') {
-        java1 = false;
-    }
-      } 
-    }
     String ignoreTCLProp = OptionConverter.getSystemProperty("log4j.ignoreTCL", null);
     if(ignoreTCLProp != null) {
       ignoreTCL = OptionConverter.toBoolean(ignoreTCLProp, true);      

src/site/apt/index.apt

@@ -32,6 +32,8 @@ Java Version Incompatibilities
 	{{{https://blogs.apache.org/logging/entry/moving_on_to_log4j_2}Log4j 1.2 is broken on Java 9}}
 	for details.
 
+	Switch to Log4J >=1.2.18 to get MDC to work.
+
 Apache log4j\u2122  1.2
 
     Welcome to Apache log4j, a logging library for Java. Apache log4j

tests/src/java/org/apache/log4j/helpers/LoaderTest.java

@@ -0,0 +1,10 @@
+package org.apache.log4j.helpers;
+
+import junit.framework.TestCase;
+
+public class LoaderTest extends TestCase {
+
+    public void testIsJava1IsAlwaysFalse() {
+        assertFalse(Loader.isJava1());
+    }
+}