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Merged
merged 1 commit into from
Sep 16, 2025
Merged

feat: support list return types in structured MCP tool content #56

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2 changes: 1 addition & 1 deletion ...c/main/java/org/springaicommunity/mcp/method/tool/AbstractAsyncMcpToolMethodCallback.java
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Original file line number Diff line number Diff line change
Expand Up @@ -251,7 +251,7 @@ protected CallToolResult mapValueToCallToolResult(Object value) {

if (this.returnMode == ReturnMode.STRUCTURED) {
String jsonOutput = JsonParser.toJson(value);
Map<String, Object> structuredOutput = JsonParser.fromJson(jsonOutput, MAP_TYPE_REFERENCE);
Object structuredOutput = JsonParser.fromJson(jsonOutput, MAP_TYPE_REFERENCE);
return CallToolResult.builder().structuredContent(structuredOutput).build();
}

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2 changes: 1 addition & 1 deletion ...rc/main/java/org/springaicommunity/mcp/method/tool/AbstractSyncMcpToolMethodCallback.java
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Expand Up @@ -162,7 +162,7 @@ protected CallToolResult processResult(Object result) {

if (this.returnMode == ReturnMode.STRUCTURED) {
String jsonOutput = JsonParser.toJson(result);
Map<String, Object> structuredOutput = JsonParser.fromJson(jsonOutput, MAP_TYPE_REFERENCE);
Object structuredOutput = JsonParser.fromJson(jsonOutput, Object.class);
return CallToolResult.builder().structuredContent(structuredOutput).build();
}

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24 changes: 23 additions & 1 deletion ...s/src/test/java/org/springaicommunity/mcp/method/tool/SyncMcpToolMethodCallbackTests.java
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Expand Up @@ -483,7 +483,7 @@ public void testConstructorParameters() {
}

@Test
public void testToolWithStructuredOutput() throws Exception {
public void testToolWithTextOutput() throws Exception {
TestToolProvider provider = new TestToolProvider();
Method method = TestToolProvider.class.getMethod("processObject", TestObject.class);
SyncMcpToolMethodCallback callback = new SyncMcpToolMethodCallback(ReturnMode.TEXT, method, provider);
Expand Down Expand Up @@ -546,6 +546,28 @@ public void testToolReturningComplexListObject() throws Exception {
[{"name":"test","value":42}]"""));
}

@Test
public void testToolReturningStructuredComplexListObject() throws Exception {
TestToolProvider provider = new TestToolProvider();
Method method = TestToolProvider.class.getMethod("returnListObjectTool", String.class, int.class);
SyncMcpToolMethodCallback callback = new SyncMcpToolMethodCallback(ReturnMode.STRUCTURED, method, provider);

McpSyncServerExchange exchange = mock(McpSyncServerExchange.class);
CallToolRequest request = new CallToolRequest("return-list-object-tool", Map.of("name", "test", "value", 42));

CallToolResult result = callback.apply(exchange, request);

assertThat(result).isNotNull();
assertThat(result.isError()).isFalse();

assertThat(result.structuredContent()).isNotNull();
assertThat(result.structuredContent()).isInstanceOf(List.class);
assertThat((List<?>) result.structuredContent()).hasSize(1);
Map<String, Object> firstEntry = ((List<Map<String, Object>>) result.structuredContent()).get(0);
assertThat(firstEntry).containsEntry("name", "test");
assertThat(firstEntry).containsEntry("value", 42);
}

@Test
public void testToolReturningStringList() throws Exception {
TestToolProvider provider = new TestToolProvider();
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28 changes: 28 additions & 0 deletions ...t/java/org/springaicommunity/mcp/method/tool/SyncStatelessMcpToolMethodCallbackTests.java
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Expand Up @@ -10,6 +10,7 @@
import java.util.Map;

import io.modelcontextprotocol.common.McpTransportContext;
import io.modelcontextprotocol.server.McpSyncServerExchange;
import io.modelcontextprotocol.spec.McpSchema.CallToolRequest;
import io.modelcontextprotocol.spec.McpSchema.CallToolResult;
import io.modelcontextprotocol.spec.McpSchema.TextContent;
Expand Down Expand Up @@ -128,6 +129,11 @@ public String toolWithContextAndRequest(McpTransportContext context, CallToolReq
return "Context present, Tool: " + request.name();
}

@McpTool(name = "return-list-object-tool", description = "Tool that returns a list of complex objects")
public List<TestObject> returnListObjectTool(String name, int value) {
return List.of(new TestObject(name, value));
}

/**
* Tool with McpMeta parameter
*/
Expand Down Expand Up @@ -543,6 +549,28 @@ public void testToolReturningComplexObject() throws Exception {
assertThat((Map<String, Object>) result.structuredContent()).containsEntry("value", 42);
}

@Test
public void testToolReturningStructuredComplexListObject() throws Exception {
TestToolProvider provider = new TestToolProvider();
Method method = TestToolProvider.class.getMethod("returnListObjectTool", String.class, int.class);
SyncMcpToolMethodCallback callback = new SyncMcpToolMethodCallback(ReturnMode.STRUCTURED, method, provider);

McpSyncServerExchange exchange = mock(McpSyncServerExchange.class);
CallToolRequest request = new CallToolRequest("return-list-object-tool", Map.of("name", "test", "value", 42));

CallToolResult result = callback.apply(exchange, request);

assertThat(result).isNotNull();
assertThat(result.isError()).isFalse();

assertThat(result.structuredContent()).isNotNull();
assertThat(result.structuredContent()).isInstanceOf(List.class);
assertThat((List<?>) result.structuredContent()).hasSize(1);
Map<String, Object> firstEntry = ((List<Map<String, Object>>) result.structuredContent()).get(0);
assertThat(firstEntry).containsEntry("name", "test");
assertThat(firstEntry).containsEntry("value", 42);
}

@Test
public void testVoidReturnMode() throws Exception {
TestToolProvider provider = new TestToolProvider();
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41 changes: 41 additions & 0 deletions ...tions/src/test/java/org/springaicommunity/mcp/provider/tool/SyncMcpToolProviderTests.java
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Expand Up @@ -693,6 +693,47 @@ public List<CustomResult> listResponseTool(String input) {
[{"message":"Processed: test"}]"""));
}

@Test
void testToolWithStructuredListReturnType() {

record CustomResult(String message) {
}

class ListResponseTool {

@McpTool(name = "list-response", description = "Tool List response", generateOutputSchema = true)
public List<CustomResult> listResponseTool(String input) {
return List.of(new CustomResult("Processed: " + input));
}

}

ListResponseTool toolObject = new ListResponseTool();
SyncMcpToolProvider provider = new SyncMcpToolProvider(List.of(toolObject));

List<SyncToolSpecification> toolSpecs = provider.getToolSpecifications();

assertThat(toolSpecs).hasSize(1);
SyncToolSpecification toolSpec = toolSpecs.get(0);

assertThat(toolSpec.tool().name()).isEqualTo("list-response");
assertThat(toolSpec.tool().outputSchema()).isNotNull();

BiFunction<McpSyncServerExchange, CallToolRequest, McpSchema.CallToolResult> callHandler = toolSpec
.callHandler();

McpSchema.CallToolResult result = callHandler.apply(mock(McpSyncServerExchange.class),
new CallToolRequest("list-response", Map.of("input", "test")));

assertThat(result).isNotNull();
assertThat(result.isError()).isFalse();

assertThat(result.structuredContent()).isInstanceOf(List.class);
assertThat((List<?>) result.structuredContent()).hasSize(1);
Map<String, Object> firstEntry = ((List<Map<String, Object>>) result.structuredContent()).get(0);
assertThat(firstEntry).containsEntry("message", "Processed: test");
}

@Test
void testToolWithPrimitiveReturnTypeNoOutputSchema() {
class PrimitiveTool {
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40 changes: 40 additions & 0 deletions .../test/java/org/springaicommunity/mcp/provider/tool/SyncStatelessMcpToolProviderTests.java
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Expand Up @@ -692,6 +692,46 @@ public List<CustomResult> listResponseTool(String input) {
[{"message":"Processed: test"}]"""));
}

@Test
void testToolWithStructuredListReturnType() {

record CustomResult(String message) {
}

class ListResponseTool {

@McpTool(name = "list-response", description = "Tool List response", generateOutputSchema = true)
public List<CustomResult> listResponseTool(String input) {
return List.of(new CustomResult("Processed: " + input));
}

}

ListResponseTool toolObject = new ListResponseTool();
SyncStatelessMcpToolProvider provider = new SyncStatelessMcpToolProvider(List.of(toolObject));

List<SyncToolSpecification> toolSpecs = provider.getToolSpecifications();

assertThat(toolSpecs).hasSize(1);
SyncToolSpecification toolSpec = toolSpecs.get(0);

assertThat(toolSpec.tool().name()).isEqualTo("list-response");
assertThat(toolSpec.tool().outputSchema()).isNotNull();

BiFunction<McpTransportContext, CallToolRequest, McpSchema.CallToolResult> callHandler = toolSpec.callHandler();

McpSchema.CallToolResult result = callHandler.apply(mock(McpTransportContext.class),
new CallToolRequest("list-response", Map.of("input", "test")));

assertThat(result).isNotNull();
assertThat(result.isError()).isFalse();

assertThat(result.structuredContent()).isInstanceOf(List.class);
assertThat((List<?>) result.structuredContent()).hasSize(1);
Map<String, Object> firstEntry = ((List<Map<String, Object>>) result.structuredContent()).get(0);
assertThat(firstEntry).containsEntry("message", "Processed: test");
}

@Test
void testToolWithPrimitiveReturnTypeNoOutputSchema() {
class PrimitiveTool {
Expand Down