feat(McpSchema): CallToolResult and CallToolRequest usability improvements (#87)

- Add constructor to CallToolResult with one String entry
- Add a new constructor to CallToolRequest that accepts JSON string arguments
- Implement a builder pattern for CallToolResult with methods for adding content items
- Add test coverage for new functionality

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>
Co-authored-by: Christian Tzolov <christian.tzolov@broadcom.com>

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

@@ -18,6 +18,7 @@ import com.fasterxml.jackson.annotation.JsonTypeInfo;
 import com.fasterxml.jackson.annotation.JsonTypeInfo.As;
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import io.modelcontextprotocol.util.Assert;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -741,6 +742,19 @@ public final class McpSchema {
 	public record CallToolRequest(// @formatter:off
 		@JsonProperty("name") String name,
 		@JsonProperty("arguments") Map<String, Object> arguments) implements Request {
+
+		public CallToolRequest(String name, String jsonArguments) {
+			this(name, parseJsonArguments(jsonArguments));			
+		}
+
+		private static Map<String, Object> parseJsonArguments(String jsonArguments) {
+			try {
+				return OBJECT_MAPPER.readValue(jsonArguments, MAP_TYPE_REF);
+			}
+			catch (IOException e) {
+				throw new IllegalArgumentException("Invalid arguments: " + jsonArguments, e);
+			}
+		}
 	}// @formatter:off
 
 	/**
@@ -756,6 +770,103 @@ public final class McpSchema {
 	public record CallToolResult( // @formatter:off
 		@JsonProperty("content") List<Content> content,
 		@JsonProperty("isError") Boolean isError) {
+
+		/**
+		 * Creates a new instance of {@link CallToolResult} with a string containing the
+		 * tool result.
+		 *
+		 * @param content The content of the tool result. This will be mapped to a one-sized list
+		 * 				  with a {@link TextContent} element.
+		 * @param isError If true, indicates that the tool execution failed and the content contains error information.
+		 *                If false or absent, indicates successful execution.
+		 */
+		public CallToolResult(String content, Boolean isError) {
+			this(List.of(new TextContent(content)), isError);
+		}
+
+		/**
+		 * Creates a builder for {@link CallToolResult}.
+		 * @return a new builder instance
+		 */
+		public static Builder builder() {
+			return new Builder();
+		}
+
+		/**
+		 * Builder for {@link CallToolResult}.
+		 */
+		public static class Builder {
+			private List<Content> content = new ArrayList<>();
+			private Boolean isError;
+
+			/**
+			 * Sets the content list for the tool result.
+			 * @param content the content list
+			 * @return this builder
+			 */
+			public Builder content(List<Content> content) {
+				Assert.notNull(content, "content must not be null");
+				this.content = content;
+				return this;
+			}
+
+			/**
+			 * Sets the text content for the tool result.
+			 * @param textContent the text content
+			 * @return this builder
+			 */
+			public Builder textContent(List<String> textContent) {
+				Assert.notNull(textContent, "textContent must not be null");
+				textContent.stream()
+					.map(TextContent::new)
+					.forEach(this.content::add);
+				return this;
+			}
+
+			/**
+			 * Adds a content item to the tool result.
+			 * @param contentItem the content item to add
+			 * @return this builder
+			 */
+			public Builder addContent(Content contentItem) {
+				Assert.notNull(contentItem, "contentItem must not be null");
+				if (this.content == null) {
+					this.content = new ArrayList<>();
+				}
+				this.content.add(contentItem);
+				return this;
+			}
+
+			/**
+			 * Adds a text content item to the tool result.
+			 * @param text the text content
+			 * @return this builder
+			 */
+			public Builder addTextContent(String text) {
+				Assert.notNull(text, "text must not be null");
+				return addContent(new TextContent(text));
+			}
+
+			/**
+			 * Sets whether the tool execution resulted in an error.
+			 * @param isError true if the tool execution failed, false otherwise
+			 * @return this builder
+			 */
+			public Builder isError(Boolean isError) {
+				Assert.notNull(isError, "isError must not be null");
+				this.isError = isError;
+				return this;
+			}
+
+			/**
+			 * Builds a new {@link CallToolResult} instance.
+			 * @return a new CallToolResult instance
+			 */
+			public CallToolResult build() {
+				return new CallToolResult(content, isError);
+			}
+		}
+
 	} // @formatter:on
 
 	// ---------------------------