feat: Eliminate one deserialization step in the majority of scenarios when parsing Model response (#4003)

Fixes #4003

Auto-cherry-pick to 1.0.x

Signed-off-by: bourne7 <[email protected]>

Author: bourne7

spring-ai-model/src/main/java/org/springframework/ai/util/json/JsonParser.java

@@ -168,8 +168,22 @@ else if (javaType.isEnum()) {
 			return Enum.valueOf((Class<Enum>) javaType, value.toString());
 		}
 
-		String json = JsonParser.toJson(value);
-		return JsonParser.fromJson(json, javaType);
+		Object result = null;
+		if (value instanceof String jsonString) {
+			try {
+				result = JsonParser.fromJson(jsonString, javaType);
+			}
+			catch (Exception e) {
+				// ignore
+			}
+		}
+
+		if (result == null) {
+			String json = JsonParser.toJson(value);
+			result = JsonParser.fromJson(json, javaType);
+		}
+
+		return result;
 	}
 
 }

spring-ai-model/src/test/java/org/springframework/ai/util/json/JsonParserTests.java

@@ -16,11 +16,11 @@
 
 package org.springframework.ai.util.json;
 
-import java.lang.reflect.Type;
-
 import com.fasterxml.jackson.core.type.TypeReference;
 import org.junit.jupiter.api.Test;
 
+import java.lang.reflect.Type;
+
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 
@@ -241,6 +241,22 @@ var record = new TestRecord("John", 30);
 		assertThat(value).isEqualTo(new TestRecord("John", 30));
 	}
 
+	@Test
+	void fromStringToObject() {
+		String jsonString = """
+				{
+				    "name": "foo",
+				    "age": 7
+				}
+				""";
+		var value = JsonParser.toTypedObject(jsonString, TestSimpleObject.class);
+		assertThat(value).isOfAnyClassIn(TestSimpleObject.class);
+
+		TestSimpleObject testSimpleObject = (TestSimpleObject) value;
+		assertThat(testSimpleObject.name).isEqualTo("foo");
+		assertThat(testSimpleObject.age).isEqualTo(7);
+	}
+
 	@Test
 	void fromScientificNotationToInteger() {
 		var value = JsonParser.toTypedObject("1.5E7", Integer.class);
@@ -265,6 +281,14 @@ void doesNotDoubleSerializeValidJsonString() {
 	record TestRecord(String name, Integer age) {
 	}
 
+	static class TestSimpleObject {
+
+		public String name;
+
+		public int age;
+
+	}
+
 	enum TestEnum {
 
 		VALUE