Make code strong, version check compatibility. (#4488)

* 2.6.x test

* version check compatibility

* add comment

* revert demo changes

* update ut

* add error log

* change log level to warn

dubbo-common/src/main/java/com/alibaba/dubbo/common/Version.java

@@ -36,6 +36,8 @@ public final class Version {
 
     // Dubbo RPC protocol version, for compatibility, it must not be between 2.0.10 ~ 2.6.2
     public static final String DEFAULT_DUBBO_PROTOCOL_VERSION = "2.0.2";
+    // version 1.0.0 represents Dubbo rpc protocol before v2.6.2
+    public static final int LEGACY_DUBBO_PROTOCOL_VERSION = 10000; // 1.0.0
     // Dubbo implementation version, usually is jar version.
     private static final String VERSION = getVersion(Version.class, "");
 
@@ -78,7 +80,14 @@ public static boolean isSupportResponseAttatchment(String version) {
     public static int getIntVersion(String version) {
         Integer v = VERSION2INT.get(version);
         if (v == null) {
-            v = parseInt(version);
+            try {
+                v = parseInt(version);
+            } catch (Exception e) {
+                logger.warn("Please make sure your version value has the right format: " +
+                        "\n 1. only contains digital number: 2.0.0; \n 2. with string suffix: 2.6.7-stable. " +
+                        "\nIf you are using Dubbo before v2.6.2, the version value is the same with the jar version.");
+                v = LEGACY_DUBBO_PROTOCOL_VERSION;
+            }
             VERSION2INT.put(version, v);
         }
         return v;

dubbo-common/src/test/java/com/alibaba/dubbo/common/version/VersionTest.java

@@ -18,7 +18,6 @@
 
 
 import com.alibaba.dubbo.common.Version;
-
 import org.junit.Assert;
 import org.junit.Test;
 
@@ -34,5 +33,11 @@ public void testSupportResponseAttatchment() {
         Assert.assertTrue(Version.isSupportResponseAttatchment("2.0.2"));
         Assert.assertTrue(Version.isSupportResponseAttatchment("2.0.3"));
         Assert.assertFalse(Version.isSupportResponseAttatchment("2.0.0"));
+        Assert.assertFalse(Version.isSupportResponseAttatchment("1.0.0"));
+        Assert.assertTrue(Version.isSupportResponseAttatchment("2.6.6-stable"));
+
+        Assert.assertFalse(Version.isSupportResponseAttatchment("2.0.contains"));
+        Assert.assertFalse(Version.isSupportResponseAttatchment("version.string"));
+        Assert.assertFalse(Version.isSupportResponseAttatchment("prefix2.0"));
     }
 }