fix(mcp): load json providers with fallback classloader #2155
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,70 @@ | ||
| /* | ||
| * Copyright 2024-2026 the original author or authors. | ||
| * | ||
| * Licensed under the Apache License, Version 2.0 (the "License"); | ||
| * you may not use this file except in compliance with the License. | ||
| * You may obtain a copy of the License at | ||
| * | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, | ||
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| * See the License for the specific language governing permissions and | ||
| * limitations under the License. | ||
| */ | ||
| package io.agentscope.core.tool.mcp; | ||
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| import io.modelcontextprotocol.json.McpJsonMapper; | ||
| import io.modelcontextprotocol.json.McpJsonMapperSupplier; | ||
| import io.modelcontextprotocol.json.schema.JsonSchemaValidator; | ||
| import io.modelcontextprotocol.json.schema.JsonSchemaValidatorSupplier; | ||
| import java.util.Optional; | ||
| import java.util.ServiceLoader; | ||
| import java.util.function.Supplier; | ||
|
|
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| /** | ||
| * Loads the default MCP JSON components using a class loader that can see their providers. | ||
| * | ||
| * <p>Worker threads in executable JARs may use a context class loader that cannot access nested | ||
| * dependencies. In that case, fall back to the AgentScope class loader. | ||
| */ | ||
| final class McpJsonDefaults { | ||
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| private McpJsonDefaults() {} | ||
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| static McpJsonMapper jsonMapper() { | ||
| return loadSupplier(McpJsonMapperSupplier.class, "McpJsonMapper").get(); | ||
| } | ||
|
|
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| static JsonSchemaValidator jsonSchemaValidator() { | ||
| return loadSupplier(JsonSchemaValidatorSupplier.class, "JsonSchemaValidator").get(); | ||
| } | ||
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| private static <T extends Supplier<?>> T loadSupplier( | ||
| Class<T> serviceType, String implementationType) { | ||
|
Collaborator
There was a problem hiding this comment. [nitpick] The parameter name |
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| ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader(); | ||
| Optional<T> supplier = loadFirst(serviceType, contextClassLoader); | ||
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| ClassLoader agentScopeClassLoader = McpJsonDefaults.class.getClassLoader(); | ||
| if (supplier.isEmpty() && agentScopeClassLoader != contextClassLoader) { | ||
| supplier = loadFirst(serviceType, agentScopeClassLoader); | ||
| } | ||
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|
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| return supplier.orElseThrow( | ||
| () -> | ||
| new IllegalStateException( | ||
| "No default " + implementationType + " implementation found")); | ||
| } | ||
|
|
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| private static <T> Optional<T> loadFirst(Class<T> serviceType, ClassLoader classLoader) { | ||
| if (classLoader == null) { | ||
| return Optional.empty(); | ||
| } | ||
| try { | ||
| return ServiceLoader.load(serviceType, classLoader).findFirst(); | ||
| } catch (java.util.ServiceConfigurationError | LinkageError e) { | ||
| return Optional.empty(); | ||
| } | ||
| } | ||
| } | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,136 @@ | ||
| /* | ||
| * Copyright 2024-2026 the original author or authors. | ||
| * | ||
| * Licensed under the Apache License, Version 2.0 (the "License"); | ||
| * you may not use this file except in compliance with the License. | ||
| * You may obtain a copy of the License at | ||
| * | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, | ||
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| * See the License for the specific language governing permissions and | ||
| * limitations under the License. | ||
| */ | ||
| package io.agentscope.core.tool.mcp; | ||
|
|
||
| import static org.junit.jupiter.api.Assertions.assertEquals; | ||
| import static org.junit.jupiter.api.Assertions.assertInstanceOf; | ||
| import static org.junit.jupiter.api.Assertions.assertNotNull; | ||
| import static org.junit.jupiter.api.Assertions.assertThrows; | ||
| import static org.junit.jupiter.api.Assertions.assertTrue; | ||
|
|
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| import io.modelcontextprotocol.json.McpJsonMapperSupplier; | ||
| import io.modelcontextprotocol.json.schema.JsonSchemaValidatorSupplier; | ||
| import java.lang.reflect.InvocationTargetException; | ||
| import java.lang.reflect.Method; | ||
| import java.net.URL; | ||
| import java.net.URLClassLoader; | ||
| import java.nio.file.Files; | ||
| import java.nio.file.Path; | ||
| import java.util.ServiceLoader; | ||
| import java.util.function.Supplier; | ||
| import org.junit.jupiter.api.Test; | ||
| import org.junit.jupiter.api.io.TempDir; | ||
|
|
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| class McpJsonDefaultsTest { | ||
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| @Test | ||
| void shouldResolveProvidersFromContextClassLoader() { | ||
| assertNotNull(McpJsonDefaults.jsonMapper()); | ||
| assertNotNull(McpJsonDefaults.jsonSchemaValidator()); | ||
| } | ||
|
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| @Test | ||
| void shouldFallbackWhenContextClassLoaderCannotSeeMcpProviders() { | ||
| ClassLoader originalClassLoader = Thread.currentThread().getContextClassLoader(); | ||
| ClassLoader isolatedClassLoader = new ClassLoader(null) {}; | ||
|
|
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| assertTrue( | ||
| ServiceLoader.load(McpJsonMapperSupplier.class, isolatedClassLoader) | ||
| .findFirst() | ||
| .isEmpty()); | ||
| assertTrue( | ||
| ServiceLoader.load(JsonSchemaValidatorSupplier.class, isolatedClassLoader) | ||
| .findFirst() | ||
| .isEmpty()); | ||
|
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| try { | ||
| Thread.currentThread().setContextClassLoader(isolatedClassLoader); | ||
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| assertNotNull(McpJsonDefaults.jsonMapper()); | ||
| assertNotNull(McpJsonDefaults.jsonSchemaValidator()); | ||
| assertNotNull( | ||
| McpClientBuilder.create("isolated-loader") | ||
| .stdioTransport("echo", "test") | ||
| .buildSync()); | ||
| } finally { | ||
| Thread.currentThread().setContextClassLoader(originalClassLoader); | ||
| } | ||
| } | ||
|
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| @Test | ||
| void shouldFallbackWhenContextClassLoaderIsNull() { | ||
| ClassLoader originalClassLoader = Thread.currentThread().getContextClassLoader(); | ||
| try { | ||
| Thread.currentThread().setContextClassLoader(null); | ||
|
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| assertNotNull(McpJsonDefaults.jsonMapper()); | ||
| assertNotNull(McpJsonDefaults.jsonSchemaValidator()); | ||
| } finally { | ||
| Thread.currentThread().setContextClassLoader(originalClassLoader); | ||
| } | ||
| } | ||
|
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| @Test | ||
| void shouldFallbackWhenContextClassLoaderHasBrokenServiceDeclaration(@TempDir Path tempDir) | ||
| throws Exception { | ||
| writeServiceFile(tempDir, McpJsonMapperSupplier.class.getName(), "missing.DoesNotExist"); | ||
|
|
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| ClassLoader originalClassLoader = Thread.currentThread().getContextClassLoader(); | ||
| try (URLClassLoader brokenClassLoader = | ||
| new URLClassLoader(new URL[] {tempDir.toUri().toURL()}, null)) { | ||
| Thread.currentThread().setContextClassLoader(brokenClassLoader); | ||
|
|
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| assertNotNull(McpJsonDefaults.jsonMapper()); | ||
| } finally { | ||
| Thread.currentThread().setContextClassLoader(originalClassLoader); | ||
| } | ||
| } | ||
|
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| @Test | ||
| void shouldThrowWhenNoDefaultSupplierIsAvailable() throws Exception { | ||
| Method loadSupplier = | ||
| McpJsonDefaults.class.getDeclaredMethod("loadSupplier", Class.class, String.class); | ||
| loadSupplier.setAccessible(true); | ||
|
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| ClassLoader originalClassLoader = Thread.currentThread().getContextClassLoader(); | ||
| try { | ||
| Thread.currentThread().setContextClassLoader(McpJsonDefaults.class.getClassLoader()); | ||
|
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| InvocationTargetException exception = | ||
| assertThrows( | ||
| InvocationTargetException.class, | ||
| () -> | ||
| loadSupplier.invoke( | ||
| null, MissingSupplier.class, "MissingSupplier")); | ||
|
|
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| IllegalStateException cause = | ||
| assertInstanceOf(IllegalStateException.class, exception.getCause()); | ||
| assertEquals("No default MissingSupplier implementation found", cause.getMessage()); | ||
| } finally { | ||
| Thread.currentThread().setContextClassLoader(originalClassLoader); | ||
| } | ||
| } | ||
|
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| private static void writeServiceFile(Path root, String serviceName, String providerName) | ||
| throws Exception { | ||
| Path serviceDirectory = root.resolve("META-INF/services"); | ||
| Files.createDirectories(serviceDirectory); | ||
| Files.writeString( | ||
| serviceDirectory.resolve(serviceName), providerName + System.lineSeparator()); | ||
| } | ||
|
|
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| private interface MissingSupplier extends Supplier<Object> {} | ||
| } |
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[nitpick]
jsonMapper()andjsonSchemaValidator()invokeServiceLoader.load()on every call. Since builder methods are typically called once per client andServiceLoader.load()is lightweight, this is acceptable. However, if clients are created frequently, consider caching the resolved supplier with a lazy-holder orstatic finalfield to avoid repeated classpath scanning. Note:ServiceLoader.load()+findFirst()should be deterministic for a given classloader, so caching is safe.