support for concatenation with String via operator '+' - for Ramnivas.

org.springframework.expression/src/main/java/org/springframework/expression/spel/ast/OpPlus.java

@@ -73,6 +73,14 @@ public class OpPlus extends Operator {
 				}
 			} else if (operandOne instanceof String && operandTwo instanceof String) {
 				return new TypedValue(new StringBuilder((String) operandOne).append((String) operandTwo).toString(),STRING_TYPE_DESCRIPTOR);
+			} else if (operandOne instanceof String) {
+				StringBuilder result = new StringBuilder((String)operandOne);
+				result.append((operandTwo==null?"null":operandTwo.toString()));
+				return new TypedValue(result.toString(),STRING_TYPE_DESCRIPTOR);				
+			} else if (operandTwo instanceof String) {
+				StringBuilder result = new StringBuilder((operandOne==null?"null":operandOne.toString()));
+				result.append((String)operandTwo);
+				return new TypedValue(result.toString(),STRING_TYPE_DESCRIPTOR);								
 			}
 			return state.operate(Operation.ADD, operandOne, operandTwo);
 		}

org.springframework.expression/src/test/java/org/springframework/expression/spel/OperatorOverloaderTests.java

@@ -55,7 +55,7 @@ public class OperatorOverloaderTests extends ExpressionTestCase {
 	@Test
 	public void testSimpleOperations() throws Exception {
 		// no built in support for this:
-		evaluateAndCheckError("'abc'+true",SpelMessage.OPERATOR_NOT_SUPPORTED_BETWEEN_TYPES);
+		evaluateAndCheckError("'abc'-true",SpelMessage.OPERATOR_NOT_SUPPORTED_BETWEEN_TYPES);
 
 		StandardEvaluationContext eContext = TestScenarioCreator.getTestEvaluationContext();
 		eContext.setOperatorOverloader(new StringAndBooleanAddition());
@@ -65,5 +65,8 @@ public class OperatorOverloaderTests extends ExpressionTestCase {
 
 		expr = (SpelExpression)parser.parseExpression("'abc'-true");
 		Assert.assertEquals("abc",expr.getValue(eContext));
+		
+		expr = (SpelExpression)parser.parseExpression("'abc'+null");
+		Assert.assertEquals("abcnull",expr.getValue(eContext));
 	}
 }

org.springframework.expression/src/test/java/org/springframework/expression/spel/OperatorTests.java

@@ -153,9 +153,10 @@ public class OperatorTests extends ExpressionTestCase {
 		evaluate("3.0f + 5.0f", 8.0d, Double.class);
 		evaluate("3.0d + 5.0d", 8.0d, Double.class);
 
-		evaluateAndCheckError("'ab' + 2", SpelMessage.OPERATOR_NOT_SUPPORTED_BETWEEN_TYPES);
-		evaluateAndCheckError("2+'a' ", SpelMessage.OPERATOR_NOT_SUPPORTED_BETWEEN_TYPES);
-		evaluateAndCheckError("2+'ab'",SpelMessage.OPERATOR_NOT_SUPPORTED_BETWEEN_TYPES);
+		evaluate("'ab' + 2", "ab2", String.class);
+		evaluate("2 + 'a'", "2a", String.class);
+		evaluate("'ab' + null", "abnull", String.class);
+		evaluate("null + 'ab'", "nullab", String.class);
 		
 		// AST:
 		SpelExpression expr = (SpelExpression)parser.parseExpression("+3");