refactor(mcp): remove redundant type field from Content implementations (#27)

- The type field and associated methods were redundant in Content implementations (TextContent, ImageContent, EmbeddedResource)
  as the type information is already handled by Jackson's polymorphic type handling via @JsonSubTypes annotation.
- Add default implementation that returns the appropriate type string based on the implementing class (text, image, or resource)
- Added comprehensive unit tests for McpSchema to validate serialization/deserialization behavior of all schema components.
- Add deserialization tests for all content types
- Add json-unit-assertj for flexible JSON testing -  ignores array order and extra array items, reducing test brittleness while
maintaining functional validation.

Resolves #26
Resolve spring-projects/spring-ai#2350

Signed-off-by: Christian Tzolov <[email protected]>

Author: tzolov

mcp/pom.xml

@@ -11,7 +11,7 @@
 	<artifactId>mcp</artifactId>
 	<packaging>jar</packaging>
 	<name>Java MCP SDK</name>
-	<description>Java SDK implementation of the Model Context Protocol, enabling seamless integration with language models and AI tools</description>	
+	<description>Java SDK implementation of the Model Context Protocol, enabling seamless integration with language models and AI tools</description>
 	<url>https://github.com/modelcontextprotocol/java-sdk</url>
 
 	<scm>
@@ -51,7 +51,7 @@
 					</execution>
 				</executions>
 			</plugin>
-			
+
 			<plugin>
 				<groupId>org.apache.maven.plugins</groupId>
 				<artifactId>maven-jar-plugin</artifactId>
@@ -158,12 +158,20 @@
 			<scope>test</scope>
 		</dependency>
 
+		<dependency>
+			<groupId>net.javacrumbs.json-unit</groupId>
+			<artifactId>json-unit-assertj</artifactId>
+			<version>${json-unit-assertj.version}</version>
+			<scope>test</scope>
+		</dependency>
+
+
 		<!-- Used by the HttpServletSseServerTransport -->
 		<dependency>
 			<groupId>jakarta.servlet</groupId>
 			<artifactId>jakarta.servlet-api</artifactId>
 			<version>${jakarta.servlet.version}</version>
-			<scope>provided</scope>		
+			<scope>provided</scope>
 		</dependency>
 
 		<!-- Tomcat dependencies for testing -->
@@ -183,4 +191,4 @@
 	</dependencies>
 
 
-</project>
+</project>

mcp/src/main/java/io/modelcontextprotocol/spec/McpSchema.java

@@ -964,61 +964,45 @@ public record CompleteCompletion(// @formatter:off
 			@JsonSubTypes.Type(value = EmbeddedResource.class, name = "resource") })
 	public sealed interface Content permits TextContent, ImageContent, EmbeddedResource {
 
-		String type();
+		default String type() {
+			if (this instanceof TextContent) {
+				return "text";
+			}
+			else if (this instanceof ImageContent) {
+				return "image";
+			}
+			else if (this instanceof EmbeddedResource) {
+				return "resource";
+			}
+			throw new IllegalArgumentException("Unknown content type: " + this);
+		}
 
 	}
 
 	@JsonInclude(JsonInclude.Include.NON_ABSENT)
 	public record TextContent( // @formatter:off
 		@JsonProperty("audience") List<Role> audience,
 		@JsonProperty("priority") Double priority,
-		@JsonProperty("type") String type,
 		@JsonProperty("text") String text) implements Content { // @formatter:on
 
-		public TextContent {
-			type = "text";
-		}
-
-		public String type() {
-			return type;
-		}
-
 		public TextContent(String content) {
-			this(null, null, "text", content);
+			this(null, null, content);
 		}
 	}
 
 	@JsonInclude(JsonInclude.Include.NON_ABSENT)
 	public record ImageContent( // @formatter:off
 		@JsonProperty("audience") List<Role> audience,
 		@JsonProperty("priority") Double priority,
-		@JsonProperty("type") String type,
 		@JsonProperty("data") String data,
 		@JsonProperty("mimeType") String mimeType) implements Content { // @formatter:on
-
-		public ImageContent {
-			type = "image";
-		}
-
-		public String type() {
-			return type;
-		}
 	}
 
 	@JsonInclude(JsonInclude.Include.NON_ABSENT)
 	public record EmbeddedResource( // @formatter:off
 		@JsonProperty("audience") List<Role> audience,
 		@JsonProperty("priority") Double priority,
-		@JsonProperty("type") String type,
 		@JsonProperty("resource") ResourceContents resource) implements Content { // @formatter:on
-
-		public EmbeddedResource {
-			type = "resource";
-		}
-
-		public String type() {
-			return type;
-		}
 	}
 
 	// ---------------------------