Fix #1948 can force deser Locale use java style

src/main/java/com/fasterxml/jackson/databind/deser/std/FromStringDeserializer.java

@@ -220,6 +220,13 @@ public static class Std extends FromStringDeserializer<Object>
         public final static int STD_INET_ADDRESS = 11;
         public final static int STD_INET_SOCKET_ADDRESS = 12;
         public final static int STD_STRING_BUILDER = 13;
+        /**
+         * If you are using java's {@linkplain Locale#toString()} serialize Locale 
+         * (split language, country and variant with '_')<br>
+         * You can force jackson deserialize String to Locale with java Locale style.<br>
+         * config: {@linkplain System#setProperty(String, String) System.setProperty("jackson.std.locale.de.java", "not empty")} 
+         */
+        public final static String STD_LOCALE_DE_JAVA = "jackson.std.locale.de.java";
 
         protected final int _kind;
 
@@ -255,6 +262,10 @@ protected Object _deserialize(String value, DeserializationContext ctxt) throws
                 return Pattern.compile(value);
             case STD_LOCALE:
                 {
+                    if (!System.getProperty(STD_LOCALE_DE_JAVA, "").isEmpty()) {
+                        return deJavaLocale(value);
+                    }
+
                     int ix = _firstHyphenOrUnderscore(value);
                     if (ix < 0) { // single argument
                         return new Locale(value);
@@ -330,5 +341,30 @@ protected int _firstHyphenOrUnderscore(String str)
             }
             return -1;
         }
+
+        /** see {@link Locale#toString()}, but ignore extends */
+        private Locale deJavaLocale(String value) {
+            if (value.isEmpty()) {
+                return new Locale("");
+            }
+
+            int extStart = value.indexOf("_#");
+            if (extStart != -1) value = value.substring(0, extStart);
+
+            String language = value, country = "", variant = "";
+            int pos1 = value.indexOf('_');
+            if (pos1 != -1) {
+                language = value.substring(0, pos1++);
+
+                int pos2 = value.indexOf('_', pos1);
+                if (pos2 == -1) {
+                    country = value.substring(pos1);
+                } else {
+                    country = value.substring(pos1, pos2);
+                    variant = value.substring(pos2 + 1);
+                }
+            }
+            return new Locale(language, country, variant);
+        }
     }
 }

src/test/java/com/fasterxml/jackson/databind/deser/jdk/JDKStringLikeTypesTest.java

@@ -17,6 +17,7 @@
 
 import com.fasterxml.jackson.databind.*;
 import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
+import com.fasterxml.jackson.databind.deser.std.FromStringDeserializer;
 import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
 import com.fasterxml.jackson.databind.exc.InvalidFormatException;
 import com.fasterxml.jackson.databind.module.SimpleModule;
@@ -132,6 +133,23 @@ public void testFile() throws Exception
 
     public void testLocale() throws IOException
     {
+        // [databind #1948]
+        String deJavaKey = FromStringDeserializer.Std.STD_LOCALE_DE_JAVA;
+        String old = System.setProperty(deJavaKey, "1");
+        try {
+            assertLocale(new Locale(""));
+            assertLocale(new Locale("en"));
+            assertLocale(new Locale("en", "US"));
+            assertLocale(new Locale("zh", "CN"));
+            assertLocale(new Locale("zh-hant", "CN"));
+        } finally {
+            if (old == null) {
+                System.getProperties().remove(deJavaKey);
+            } else {
+                System.setProperty(deJavaKey, old);
+            }
+        }
+
         assertEquals(new Locale("en"), MAPPER.readValue(quote("en"), Locale.class));
         assertEquals(new Locale("es", "ES"), MAPPER.readValue(quote("es_ES"), Locale.class));
         assertEquals(new Locale("FI", "fi", "savo"),
@@ -144,6 +162,10 @@ public void testLocale() throws IOException
         assertSame(Locale.ROOT, loc);
     }
 
+    private void assertLocale(Locale loc) throws IOException {
+        assertEquals(loc, MAPPER.readValue(MAPPER.writeValueAsString(loc), Locale.class));
+    }
+
     public void testCharSequence() throws IOException
     {
         CharSequence cs = MAPPER.readValue("\"abc\"", CharSequence.class);