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Make JSON Mapper SPI (#1)
This pull request creates two modules, `mcp-json` and `mcp-json-jackson`. It removes the `com.fasterxml.jackson.core:jackson-databind` and `com.networknt:json-schema-validator` dependencies from the `mcp` module. The `mcp` module now only depends on `com.fasterxml.jackson.core:jackson-annotations`. To use Jackson, you have to add `mcp-jackson` to your dependencies in addition to `mcp`. I added the dependency `mcp-jackson` to both `mcp-spring-mvc` and `mcp-spring-webflux` to avoid a breaking change in those modules. It provides two [SPI](https://docs.oracle.com/javase/tutorial/sound/SPI-intro.html) `JsonSchemaValidatorSupplier` and `JacksonJsonSchemaValidatorSupplier` to allow easy replacement for consumers who don't want to use Jackson. This pull request also ensures no `McpJsonMapper` is instantiated if one is provided via a builder method. Only if the builders don't receive a `McpJsonMapper` mapper, one is instantiated in the `build` method of the builder. The logic behind this is to allow frameworks to provide a `McpJsonMapper` mapper singleton implementation and feed it to the builders without paying the price of instantiating `McpJsonMappers`, which will not be used. The goal is to be able to use the `ObjectMapper` singleton of an application also for the MCP code. ## Breaking changes - This pull request also removes the deprecated `Tool` constructors, and it updates every test to use the builder API to instantiate tools. - Several constructors taking an ObjectMapper or constructor which forced the instantiation of a generic `McpJsonMapper` have been removed.
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‎mcp-json-jackson/pom.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>io.modelcontextprotocol.sdk</groupId>
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<artifactId>mcp-parent</artifactId>
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<version>0.13.0-SNAPSHOT</version>
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</parent>
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<artifactId>mcp-json-jackson</artifactId>
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<packaging>jar</packaging>
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<name>Java MCP SDK JSON Jackson</name>
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<description>Java MCP SDK JSON implementation based on Jackson</description>
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<url>https://github.com/modelcontextprotocol/java-sdk</url>
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<scm>
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<url>https://github.com/modelcontextprotocol/java-sdk</url>
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<connection>git://github.com/modelcontextprotocol/java-sdk.git</connection>
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<developerConnection>[email protected]/modelcontextprotocol/java-sdk.git</developerConnection>
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</scm>
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<build>
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<plugins>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-jar-plugin</artifactId>
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<configuration>
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<archive>
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<manifest>
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<addDefaultImplementationEntries>true</addDefaultImplementationEntries>
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</manifest>
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</archive>
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</configuration>
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</plugin>
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</plugins>
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</build>
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<dependencies>
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<dependency>
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<groupId>io.modelcontextprotocol.sdk</groupId>
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<artifactId>mcp-json</artifactId>
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<version>0.13.0-SNAPSHOT</version>
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</dependency>
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<dependency>
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<groupId>com.fasterxml.jackson.core</groupId>
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<artifactId>jackson-databind</artifactId>
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<version>${jackson.version}</version>
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</dependency>
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<dependency>
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<groupId>com.networknt</groupId>
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<artifactId>json-schema-validator</artifactId>
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<version>${json-schema-validator.version}</version>
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</dependency>
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</dependencies>
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</project>

‎mcp/src/main/java/io/modelcontextprotocol/spec/json/jackson/JacksonMcpJsonMapper.java‎ renamed to ‎mcp-json-jackson/src/main/java/io/modelcontextprotocol/json/jackson/JacksonMcpJsonMapper.java‎

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package io.modelcontextprotocol.spec.json.jackson;
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package io.modelcontextprotocol.json.jackson;
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import com.fasterxml.jackson.databind.JavaType;
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import com.fasterxml.jackson.databind.ObjectMapper;
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import io.modelcontextprotocol.spec.json.McpJsonMapper;
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import io.modelcontextprotocol.spec.json.TypeRef;
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import io.modelcontextprotocol.json.McpJsonMapper;
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import io.modelcontextprotocol.json.TypeRef;
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import java.io.IOException;
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‎mcp-json-jackson/src/main/java/io/modelcontextprotocol/json/jackson/JacksonMcpJsonMapperSupplier.java‎

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package io.modelcontextprotocol.json.jackson;
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import io.modelcontextprotocol.json.McpJsonMapper;
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import io.modelcontextprotocol.json.McpJsonMapperSupplier;
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public class JacksonMcpJsonMapperSupplier implements McpJsonMapperSupplier {
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@Override
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public McpJsonMapper get() {
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return new JacksonMcpJsonMapper(new com.fasterxml.jackson.databind.ObjectMapper());
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}
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}

‎mcp/src/main/java/io/modelcontextprotocol/spec/DefaultJsonSchemaValidator.java‎ renamed to ‎mcp-json-jackson/src/main/java/io/modelcontextprotocol/json/schema/jackson/DefaultJsonSchemaValidator.java‎

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* Copyright 2024-2024 the original author or authors.
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*/
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package io.modelcontextprotocol.spec;
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package io.modelcontextprotocol.json.schema.jackson;
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import java.util.Map;
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import java.util.Set;
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import java.util.concurrent.ConcurrentHashMap;
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import io.modelcontextprotocol.json.schema.JsonSchemaValidator;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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import com.networknt.schema.SpecVersion;
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import com.networknt.schema.ValidationMessage;
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import io.modelcontextprotocol.util.Assert;
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import io.modelcontextprotocol.spec.json.McpJsonMapper;
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import io.modelcontextprotocol.spec.json.jackson.JacksonMcpJsonMapper;
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/**
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* Default implementation of the {@link JsonSchemaValidator} interface. This class
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* provides methods to validate structured content against a JSON schema. It uses the
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this.schemaCache = new ConcurrentHashMap<>();
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}
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/**
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* Alternate constructor that accepts a JsonMapper. If the mapper is backed by
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* Jackson, the underlying ObjectMapper will be reused; otherwise a new ObjectMapper
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* will be created for schema validation only.
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*/
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public DefaultJsonSchemaValidator(McpJsonMapper jsonMapper) {
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ObjectMapper mapper;
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if (jsonMapper instanceof JacksonMcpJsonMapper jacksonJsonMapper) {
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mapper = jacksonJsonMapper.getObjectMapper();
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}
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else {
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mapper = new ObjectMapper();
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}
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this.objectMapper = mapper;
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this.schemaFactory = JsonSchemaFactory.getInstance(SpecVersion.VersionFlag.V202012);
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this.schemaCache = new ConcurrentHashMap<>();
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}
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@Override
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public ValidationResponse validate(Map<String, Object> schema, Map<String, Object> structuredContent) {
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Assert.notNull(schema, "Schema must not be null");
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Assert.notNull(structuredContent, "Structured content must not be null");
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if (schema == null) {
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throw new IllegalArgumentException("Schema must not be null");
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}
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if (structuredContent == null) {
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throw new IllegalArgumentException("Structured content must not be null");
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}
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try {
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‎mcp-json-jackson/src/main/java/io/modelcontextprotocol/json/schema/jackson/JacksonJsonSchemaValidatorSupplier.java‎

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package io.modelcontextprotocol.json.schema.jackson;
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import io.modelcontextprotocol.json.schema.JsonSchemaValidator;
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import io.modelcontextprotocol.json.schema.JsonSchemaValidatorSupplier;
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public class JacksonJsonSchemaValidatorSupplier implements JsonSchemaValidatorSupplier {
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@Override
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public JsonSchemaValidator get() {
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return new DefaultJsonSchemaValidator();
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}
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}

‎mcp-json-jackson/src/main/resources/META-INF/services/io.modelcontextprotocol.json.McpJsonMapperSupplier‎

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io.modelcontextprotocol.json.jackson.JacksonMcpJsonMapperSupplier

‎mcp-json-jackson/src/main/resources/META-INF/services/io.modelcontextprotocol.json.schema.JsonSchemaValidatorSupplier‎

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io.modelcontextprotocol.json.schema.jackson.JacksonJsonSchemaValidatorSupplier

‎mcp-json/pom.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>io.modelcontextprotocol.sdk</groupId>
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<artifactId>mcp-parent</artifactId>
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<version>0.13.0-SNAPSHOT</version>
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</parent>
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<artifactId>mcp-json</artifactId>
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<packaging>jar</packaging>
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<name>Java MCP SDK JSON Schema</name>
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<description>Java MCP SDK JSON Schema API</description>
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<url>https://github.com/modelcontextprotocol/java-sdk</url>
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<scm>
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<url>https://github.com/modelcontextprotocol/java-sdk</url>
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<connection>git://github.com/modelcontextprotocol/java-sdk.git</connection>
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<developerConnection>[email protected]/modelcontextprotocol/java-sdk.git</developerConnection>
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</scm>
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<build>
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<plugins>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-jar-plugin</artifactId>
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<configuration>
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<archive>
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<manifest>
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<addDefaultImplementationEntries>true</addDefaultImplementationEntries>
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</manifest>
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</archive>
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</configuration>
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</plugin>
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</plugins>
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</build>
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<dependencies>
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</dependencies>
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</project>

‎mcp/src/main/java/io/modelcontextprotocol/spec/json/McpJsonMapper.java‎ renamed to ‎mcp-json/src/main/java/io/modelcontextprotocol/json/McpJsonMapper.java‎

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package io.modelcontextprotocol.spec.json;
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package io.modelcontextprotocol.json;
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import java.io.IOException;
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import java.util.ServiceLoader;
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import java.util.concurrent.atomic.AtomicReference;
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import java.util.stream.Stream;
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/**
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* Abstraction for JSON serialization/deserialization to decouple the SDK from any
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*/
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byte[] writeValueAsBytes(Object value) throws IOException;
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/**
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* Resolves the default {@link McpJsonMapper}.
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* @return The default {@link McpJsonMapper}
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* @throws IllegalStateException If no {@link McpJsonMapper} implementation exists on
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* the classpath.
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*/
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static McpJsonMapper createDefault() {
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AtomicReference<IllegalStateException> ex = new AtomicReference<>();
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return ServiceLoader.load(McpJsonMapperSupplier.class).stream().flatMap(p -> {
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try {
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McpJsonMapperSupplier supplier = p.get();
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return Stream.ofNullable(supplier);
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}
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catch (Exception e) {
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addException(ex, e);
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return Stream.empty();
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}
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}).flatMap(jsonMapperSupplier -> {
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try {
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return Stream.of(jsonMapperSupplier.get());
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}
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catch (Exception e) {
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addException(ex, e);
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return Stream.empty();
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}
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}).findFirst().orElseThrow(() -> {
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if (ex.get() != null) {
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return ex.get();
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}
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else {
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return new IllegalStateException("No default McpJsonMapper implementation found");
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}
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});
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}
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private static void addException(AtomicReference<IllegalStateException> ref, Exception toAdd) {
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ref.updateAndGet(existing -> {
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if (existing == null) {
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return new IllegalStateException("Failed to initialize default McpJsonMapper", toAdd);
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}
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else {
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existing.addSuppressed(toAdd);
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return existing;
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}
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});
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}
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}

‎mcp-json/src/main/java/io/modelcontextprotocol/json/McpJsonMapperSupplier.java‎

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package io.modelcontextprotocol.json;
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import java.util.function.Supplier;
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/**
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* Strategy interface for resolving a {@link McpJsonMapper}.
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*/
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public interface McpJsonMapperSupplier extends Supplier<McpJsonMapper> {
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}

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