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feat: Enhance LangChain4j with MCP tool handling #803

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feat: Enhance LangChain4j with MCP tool handling #803

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25 changes: 21 additions & 4 deletions contrib/langchain4j/src/main/java/com/google/adk/models/langchain4j/LangChain4j.java
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.google.adk.JsonBaseModel;
import com.google.adk.models.BaseLlm;
import com.google.adk.models.BaseLlmConnection;
import com.google.adk.models.LlmRequest;
Expand Down Expand Up @@ -428,8 +429,26 @@ private List<ToolSpecification> toToolSpecifications(LlmRequest llmRequest) {
baseTool -> {
if (baseTool.declaration().isPresent()) {
FunctionDeclaration functionDeclaration = baseTool.declaration().get();
if (functionDeclaration.parameters().isPresent()) {
Schema schema = functionDeclaration.parameters().get();
Schema schema = null;
if (functionDeclaration.parametersJsonSchema().isPresent()) {
Object jsonSchemaObj = functionDeclaration.parametersJsonSchema().get();
try {
if (jsonSchemaObj instanceof Schema) {
schema = (Schema) jsonSchemaObj;
} else {
ObjectMapper adkMapper = JsonBaseModel.getMapper();
String jsonSchemaStr = adkMapper.writeValueAsString(jsonSchemaObj);
schema = adkMapper.readValue(jsonSchemaStr, Schema.class);
Comment on lines +439 to +441
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@gemini-code-assist gemini-code-assist bot Jan 30, 2026

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medium

For efficiency and conciseness, you can directly convert the jsonSchemaObj to a Schema object using ObjectMapper.convertValue(). This avoids the intermediate step of serializing to a JSON string and then deserializing back.

Suggested change
ObjectMapper adkMapper = JsonBaseModel.getMapper();
String jsonSchemaStr = adkMapper.writeValueAsString(jsonSchemaObj);
schema = adkMapper.readValue(jsonSchemaStr, Schema.class);
schema = JsonBaseModel.getMapper().convertValue(jsonSchemaObj, Schema.class);

}
} catch (Exception e) {
throw new IllegalStateException(
"Failed to convert parametersJsonSchema to Schema: " + e.getMessage(), e);
}
} else if (functionDeclaration.parameters().isPresent()) {
schema = functionDeclaration.parameters().get();
}

if (schema != null) {
ToolSpecification toolSpecification =
ToolSpecification.builder()
.name(baseTool.name())
Expand All @@ -438,11 +457,9 @@ private List<ToolSpecification> toToolSpecifications(LlmRequest llmRequest) {
.build();
toolSpecifications.add(toolSpecification);
} else {
// TODO exception or something else?
throw new IllegalStateException("Tool lacking parameters: " + baseTool);
}
} else {
// TODO exception or something else?
throw new IllegalStateException("Tool lacking declaration: " + baseTool);
}
});
Expand Down
127 changes: 127 additions & 0 deletions contrib/langchain4j/src/test/java/com/google/adk/models/langchain4j/LangChain4jTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -688,4 +688,131 @@ void testGenerateContentWithStructuredResponseJsonSchema() {
final UserMessage userMessage = (UserMessage) capturedRequest.messages().get(0);
assertThat(userMessage.singleText()).isEqualTo("Give me information about John Doe");
}

@Test
@DisplayName("Should handle MCP tools with parametersJsonSchema")
void testGenerateContentWithMcpToolParametersJsonSchema() {
// Given
// Create a mock BaseTool for MCP tool
final com.google.adk.tools.BaseTool mcpTool = mock(com.google.adk.tools.BaseTool.class);
when(mcpTool.name()).thenReturn("mcpTool");
when(mcpTool.description()).thenReturn("An MCP tool");

// Create a mock FunctionDeclaration
final FunctionDeclaration functionDeclaration = mock(FunctionDeclaration.class);
when(mcpTool.declaration()).thenReturn(Optional.of(functionDeclaration));

// MCP tools use parametersJsonSchema() instead of parameters()
// Create a JSON schema object (Map representation)
final Map<String, Object> jsonSchemaMap =
Map.of(
"type",
"object",
"properties",
Map.of("city", Map.of("type", "string", "description", "City name")),
"required",
List.of("city"));

// Mock parametersJsonSchema() to return the JSON schema object
when(functionDeclaration.parametersJsonSchema()).thenReturn(Optional.of(jsonSchemaMap));
when(functionDeclaration.parameters()).thenReturn(Optional.empty());

// Create a LlmRequest with the MCP tool
final LlmRequest llmRequest =
LlmRequest.builder()
.contents(List.of(Content.fromParts(Part.fromText("Use the MCP tool"))))
.tools(Map.of("mcpTool", mcpTool))
.build();

// Mock the AI response
final AiMessage aiMessage = AiMessage.from("Tool executed successfully");

final ChatResponse chatResponse = mock(ChatResponse.class);
when(chatResponse.aiMessage()).thenReturn(aiMessage);
when(chatModel.chat(any(ChatRequest.class))).thenReturn(chatResponse);

// When
final LlmResponse response = langChain4j.generateContent(llmRequest, false).blockingFirst();

// Then
// Verify the response
assertThat(response).isNotNull();
assertThat(response.content()).isPresent();
assertThat(response.content().get().text()).isEqualTo("Tool executed successfully");

// Verify the request was built correctly with the tool specification
final ArgumentCaptor<ChatRequest> requestCaptor = ArgumentCaptor.forClass(ChatRequest.class);
verify(chatModel).chat(requestCaptor.capture());
final ChatRequest capturedRequest = requestCaptor.getValue();

// Verify tool specifications were created from parametersJsonSchema
assertThat(capturedRequest.toolSpecifications()).isNotEmpty();
assertThat(capturedRequest.toolSpecifications().get(0).name()).isEqualTo("mcpTool");
assertThat(capturedRequest.toolSpecifications().get(0).description()).isEqualTo("An MCP tool");
}

@Test
@DisplayName("Should handle MCP tools with parametersJsonSchema when it's already a Schema")
void testGenerateContentWithMcpToolParametersJsonSchemaAsSchema() {
// Given
// Create a mock BaseTool for MCP tool
final com.google.adk.tools.BaseTool mcpTool = mock(com.google.adk.tools.BaseTool.class);
when(mcpTool.name()).thenReturn("mcpTool");
when(mcpTool.description()).thenReturn("An MCP tool");

// Create a mock FunctionDeclaration
final FunctionDeclaration functionDeclaration = mock(FunctionDeclaration.class);
when(mcpTool.declaration()).thenReturn(Optional.of(functionDeclaration));

// Create a Schema object directly (when parametersJsonSchema returns Schema)
final Schema cityPropertySchema =
Schema.builder()
.type(Type.builder().knownEnum(Type.Known.STRING).build())
.description("City name")
.build();

final Schema objectSchema =
Schema.builder()
.type(Type.builder().knownEnum(Type.Known.OBJECT).build())
.properties(Map.of("city", cityPropertySchema))
.required(List.of("city"))
.build();

// Mock parametersJsonSchema() to return Schema directly
when(functionDeclaration.parametersJsonSchema()).thenReturn(Optional.of(objectSchema));
when(functionDeclaration.parameters()).thenReturn(Optional.empty());

// Create a LlmRequest with the MCP tool
final LlmRequest llmRequest =
LlmRequest.builder()
.contents(List.of(Content.fromParts(Part.fromText("Use the MCP tool"))))
.tools(Map.of("mcpTool", mcpTool))
.build();

// Mock the AI response
final AiMessage aiMessage = AiMessage.from("Tool executed successfully");

final ChatResponse chatResponse = mock(ChatResponse.class);
when(chatResponse.aiMessage()).thenReturn(aiMessage);
when(chatModel.chat(any(ChatRequest.class))).thenReturn(chatResponse);

// When
final LlmResponse response = langChain4j.generateContent(llmRequest, false).blockingFirst();

// Then
// Verify the response
assertThat(response).isNotNull();
assertThat(response.content()).isPresent();
assertThat(response.content().get().text()).isEqualTo("Tool executed successfully");

// Verify the request was built correctly with the tool specification
final ArgumentCaptor<ChatRequest> requestCaptor = ArgumentCaptor.forClass(ChatRequest.class);
verify(chatModel).chat(requestCaptor.capture());
final ChatRequest capturedRequest = requestCaptor.getValue();

// Verify tool specifications were created from parametersJsonSchema
assertThat(capturedRequest.toolSpecifications()).isNotEmpty();
assertThat(capturedRequest.toolSpecifications().get(0).name()).isEqualTo("mcpTool");
assertThat(capturedRequest.toolSpecifications().get(0).description()).isEqualTo("An MCP tool");
}
}