refactor(server): Replace InjectorProvider with DependencyInjector for improved dependency injection

codeboyzhou · codeboyzhou · commit 6b76fcd7c701 · 2025-08-26T15:30:25.000+08:00
diff --git a/src/main/java/com/github/codeboyzhou/mcp/declarative/McpServers.java b/src/main/java/com/github/codeboyzhou/mcp/declarative/McpServers.java
@@ -1,9 +1,11 @@
 package com.github.codeboyzhou.mcp.declarative;
 
-import com.github.codeboyzhou.mcp.declarative.common.InjectorModule;
-import com.github.codeboyzhou.mcp.declarative.common.InjectorProvider;
 import com.github.codeboyzhou.mcp.declarative.configuration.McpServerConfiguration;
 import com.github.codeboyzhou.mcp.declarative.configuration.YAMLConfigurationLoader;
+import com.github.codeboyzhou.mcp.declarative.di.DependencyInjector;
+import com.github.codeboyzhou.mcp.declarative.di.DependencyInjectorProvider;
+import com.github.codeboyzhou.mcp.declarative.di.GuiceDependencyInjector;
+import com.github.codeboyzhou.mcp.declarative.di.GuiceInjectorModule;
 import com.github.codeboyzhou.mcp.declarative.server.McpServerInfo;
 import com.github.codeboyzhou.mcp.declarative.server.factory.McpSseServerFactory;
 import com.github.codeboyzhou.mcp.declarative.server.factory.McpSseServerInfo;
@@ -12,7 +14,6 @@
 import com.github.codeboyzhou.mcp.declarative.server.factory.McpStreamableServerInfo;
 import com.github.codeboyzhou.mcp.declarative.server.factory.configurable.ConfigurableMcpServerFactories;
 import com.google.inject.Guice;
-import com.google.inject.Injector;
 import io.modelcontextprotocol.util.Assert;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -23,29 +24,29 @@ public class McpServers {
 
   private static final McpServers INSTANCE = new McpServers();
 
+  private static DependencyInjector injector;
+
   private McpServers() {
     // Using singleton design pattern should have private constructor
   }
 
   public static McpServers run(Class<?> applicationMainClass, String[] args) {
-    InjectorModule module = new InjectorModule(applicationMainClass);
-    Injector injector = Guice.createInjector(module);
-    InjectorProvider.initialize(injector);
+    GuiceInjectorModule module = new GuiceInjectorModule(applicationMainClass);
+    DependencyInjector injector = new GuiceDependencyInjector(Guice.createInjector(module));
+    DependencyInjectorProvider.INSTANCE.initialize(injector);
+    McpServers.injector = injector;
     return INSTANCE;
   }
 
   public void startStdioServer(McpServerInfo serverInfo) {
-    Injector injector = InjectorProvider.getInstance().getInjector();
     injector.getInstance(McpStdioServerFactory.class).startServer(serverInfo);
   }
 
   public void startSseServer(McpSseServerInfo serverInfo) {
-    Injector injector = InjectorProvider.getInstance().getInjector();
     injector.getInstance(McpSseServerFactory.class).startServer(serverInfo);
   }
 
   public void startStreamableServer(McpStreamableServerInfo serverInfo) {
-    Injector injector = InjectorProvider.getInstance().getInjector();
     injector.getInstance(McpStreamableServerFactory.class).startServer(serverInfo);
   }
 
diff --git a/src/main/java/com/github/codeboyzhou/mcp/declarative/common/InjectorProvider.java b/src/main/java/com/github/codeboyzhou/mcp/declarative/common/InjectorProvider.java
diff --git a/src/main/java/com/github/codeboyzhou/mcp/declarative/di/DependencyInjector.java b/src/main/java/com/github/codeboyzhou/mcp/declarative/di/DependencyInjector.java
@@ -0,0 +1,10 @@
+package com.github.codeboyzhou.mcp.declarative.di;
+
+public interface DependencyInjector {
+
+  <T> T getInstance(Class<T> type);
+
+  <T> T getVariable(Class<T> type, String name);
+
+  boolean isInitialized();
+}
diff --git a/src/main/java/com/github/codeboyzhou/mcp/declarative/di/DependencyInjectorProvider.java b/src/main/java/com/github/codeboyzhou/mcp/declarative/di/DependencyInjectorProvider.java
@@ -0,0 +1,24 @@
+package com.github.codeboyzhou.mcp.declarative.di;
+
+public enum DependencyInjectorProvider {
+  INSTANCE;
+
+  private volatile DependencyInjector injector;
+
+  public DependencyInjectorProvider initialize(DependencyInjector injector) {
+    synchronized (this) {
+      if (this.injector == null) {
+        this.injector = injector;
+      }
+    }
+    return this;
+  }
+
+  public DependencyInjector getInjector() {
+    DependencyInjector current = this.injector;
+    if (current == null) {
+      throw new IllegalStateException("DependencyInjector has not been initialized yet");
+    }
+    return current;
+  }
+}
diff --git a/src/main/java/com/github/codeboyzhou/mcp/declarative/di/GuiceDependencyInjector.java b/src/main/java/com/github/codeboyzhou/mcp/declarative/di/GuiceDependencyInjector.java
@@ -0,0 +1,35 @@
+package com.github.codeboyzhou.mcp.declarative.di;
+
+import com.google.inject.Injector;
+import com.google.inject.Key;
+import com.google.inject.name.Names;
+
+public class GuiceDependencyInjector implements DependencyInjector {
+
+  private final Injector injector;
+
+  public GuiceDependencyInjector(Injector injector) {
+    this.injector = injector;
+  }
+
+  @Override
+  public <T> T getInstance(Class<T> type) {
+    if (isInitialized()) {
+      return injector.getInstance(type);
+    }
+    throw new IllegalStateException("GuiceDependencyInjector is not initialized");
+  }
+
+  @Override
+  public boolean isInitialized() {
+    return injector != null;
+  }
+
+  @Override
+  public <T> T getVariable(Class<T> type, String name) {
+    if (isInitialized()) {
+      return injector.getInstance(Key.get(type, Names.named(name)));
+    }
+    throw new IllegalStateException("GuiceDependencyInjector is not initialized");
+  }
+}
diff --git a/src/main/java/com/github/codeboyzhou/mcp/declarative/di/GuiceInjectorModule.java b/src/main/java/com/github/codeboyzhou/mcp/declarative/di/GuiceInjectorModule.java
@@ -1,4 +1,4 @@
-package com.github.codeboyzhou.mcp.declarative.common;
+package com.github.codeboyzhou.mcp.declarative.di;
 
 import static com.google.inject.Scopes.SINGLETON;
 import static java.util.stream.Collectors.toSet;
@@ -25,13 +25,13 @@
 import java.util.Set;
 import org.reflections.Reflections;
 
-public final class InjectorModule extends AbstractModule {
+public final class GuiceInjectorModule extends AbstractModule {
 
   public static final String INJECTED_VARIABLE_NAME_I18N_ENABLED = "i18nEnabled";
 
   private final Class<?> mainClass;
 
-  public InjectorModule(Class<?> mainClass) {
+  public GuiceInjectorModule(Class<?> mainClass) {
     this.mainClass = mainClass;
   }
 
diff --git a/src/main/java/com/github/codeboyzhou/mcp/declarative/server/component/AbstractMcpServerComponentFactory.java b/src/main/java/com/github/codeboyzhou/mcp/declarative/server/component/AbstractMcpServerComponentFactory.java
@@ -1,11 +1,10 @@
 package com.github.codeboyzhou.mcp.declarative.server.component;
 
-import static com.github.codeboyzhou.mcp.declarative.common.InjectorModule.INJECTED_VARIABLE_NAME_I18N_ENABLED;
+import static com.github.codeboyzhou.mcp.declarative.di.GuiceInjectorModule.INJECTED_VARIABLE_NAME_I18N_ENABLED;
 
-import com.github.codeboyzhou.mcp.declarative.common.InjectorProvider;
+import com.github.codeboyzhou.mcp.declarative.di.DependencyInjector;
+import com.github.codeboyzhou.mcp.declarative.di.DependencyInjectorProvider;
 import com.github.codeboyzhou.mcp.declarative.util.Strings;
-import com.google.inject.Key;
-import com.google.inject.name.Names;
 import java.util.Locale;
 import java.util.ResourceBundle;
 import org.slf4j.Logger;
@@ -20,14 +19,16 @@ public abstract class AbstractMcpServerComponentFactory<T> implements McpServerC
 
   protected static final String NOT_SPECIFIED = "Not Specified";
 
+  protected final DependencyInjector injector;
+
   private final ResourceBundle bundle;
 
   private final boolean i18nEnabled;
 
   protected AbstractMcpServerComponentFactory() {
     this.bundle = loadResourceBundle();
-    Key<Boolean> key = Key.get(Boolean.class, Names.named(INJECTED_VARIABLE_NAME_I18N_ENABLED));
-    this.i18nEnabled = InjectorProvider.getInstance().getInjector().getInstance(key);
+    this.injector = DependencyInjectorProvider.INSTANCE.getInjector();
+    this.i18nEnabled = injector.getVariable(Boolean.class, INJECTED_VARIABLE_NAME_I18N_ENABLED);
   }
 
   protected String resolveComponentAttributeValue(String attributeLiteralValue) {
diff --git a/src/main/java/com/github/codeboyzhou/mcp/declarative/server/component/McpServerComponentRegister.java b/src/main/java/com/github/codeboyzhou/mcp/declarative/server/component/McpServerComponentRegister.java
@@ -4,8 +4,8 @@
 import com.github.codeboyzhou.mcp.declarative.annotation.McpResource;
 import com.github.codeboyzhou.mcp.declarative.annotation.McpTool;
 import com.github.codeboyzhou.mcp.declarative.common.Immutable;
-import com.github.codeboyzhou.mcp.declarative.common.InjectorProvider;
-import com.google.inject.Injector;
+import com.github.codeboyzhou.mcp.declarative.di.DependencyInjector;
+import com.github.codeboyzhou.mcp.declarative.di.DependencyInjectorProvider;
 import io.modelcontextprotocol.server.McpSyncServer;
 import java.lang.annotation.Annotation;
 import java.lang.reflect.Method;
@@ -15,14 +15,14 @@
 
 public final class McpServerComponentRegister {
 
-  private final Injector injector;
+  private final DependencyInjector injector;
 
   private final Reflections reflections;
 
   private final Immutable<McpSyncServer> server;
 
   public McpServerComponentRegister(McpSyncServer server) {
-    this.injector = InjectorProvider.getInstance().getInjector();
+    this.injector = DependencyInjectorProvider.INSTANCE.getInjector();
     this.reflections = injector.getInstance(Reflections.class);
     this.server = Immutable.of(server);
   }
diff --git a/src/main/java/com/github/codeboyzhou/mcp/declarative/server/component/McpServerPromptFactory.java b/src/main/java/com/github/codeboyzhou/mcp/declarative/server/component/McpServerPromptFactory.java
@@ -2,7 +2,6 @@
 
 import com.github.codeboyzhou.mcp.declarative.annotation.McpPrompt;
 import com.github.codeboyzhou.mcp.declarative.annotation.McpPromptParam;
-import com.github.codeboyzhou.mcp.declarative.common.InjectorProvider;
 import com.github.codeboyzhou.mcp.declarative.util.ObjectMappers;
 import com.github.codeboyzhou.mcp.declarative.util.Strings;
 import com.github.codeboyzhou.mcp.declarative.util.Types;
@@ -35,7 +34,7 @@ public McpServerFeatures.SyncPromptSpecification create(Class<?> clazz, Method m
         (exchange, request) -> {
           Object result;
           try {
-            Object instance = InjectorProvider.getInstance().getInjector().getInstance(clazz);
+            Object instance = injector.getInstance(clazz);
             List<Object> typedValues = asTypedParameterValues(method, request.arguments());
             result = method.invoke(instance, typedValues.toArray());
           } catch (Exception e) {
diff --git a/src/main/java/com/github/codeboyzhou/mcp/declarative/server/component/McpServerResourceFactory.java b/src/main/java/com/github/codeboyzhou/mcp/declarative/server/component/McpServerResourceFactory.java
@@ -1,7 +1,6 @@
 package com.github.codeboyzhou.mcp.declarative.server.component;
 
 import com.github.codeboyzhou.mcp.declarative.annotation.McpResource;
-import com.github.codeboyzhou.mcp.declarative.common.InjectorProvider;
 import com.github.codeboyzhou.mcp.declarative.util.ObjectMappers;
 import com.github.codeboyzhou.mcp.declarative.util.Strings;
 import io.modelcontextprotocol.server.McpServerFeatures;
@@ -37,7 +36,7 @@ public McpServerFeatures.SyncResourceSpecification create(Class<?> clazz, Method
         (exchange, request) -> {
           Object result;
           try {
-            Object instance = InjectorProvider.getInstance().getInjector().getInstance(clazz);
+            Object instance = injector.getInstance(clazz);
             result = method.invoke(instance);
           } catch (Exception e) {
             log.error("Error invoking resource method", e);
diff --git a/src/main/java/com/github/codeboyzhou/mcp/declarative/server/component/McpServerToolFactory.java b/src/main/java/com/github/codeboyzhou/mcp/declarative/server/component/McpServerToolFactory.java
@@ -4,7 +4,6 @@
 import com.github.codeboyzhou.mcp.declarative.annotation.McpJsonSchemaDefinitionProperty;
 import com.github.codeboyzhou.mcp.declarative.annotation.McpTool;
 import com.github.codeboyzhou.mcp.declarative.annotation.McpToolParam;
-import com.github.codeboyzhou.mcp.declarative.common.InjectorProvider;
 import com.github.codeboyzhou.mcp.declarative.enums.JsonSchemaDataType;
 import com.github.codeboyzhou.mcp.declarative.util.ObjectMappers;
 import com.github.codeboyzhou.mcp.declarative.util.Strings;
@@ -51,7 +50,7 @@ public McpServerFeatures.SyncToolSpecification create(Class<?> clazz, Method met
               Object result;
               boolean isError = false;
               try {
-                Object instance = InjectorProvider.getInstance().getInjector().getInstance(clazz);
+                Object instance = injector.getInstance(clazz);
                 List<Object> typedValues = asTypedParameterValues(method, request.arguments());
                 result = method.invoke(instance, typedValues.toArray());
               } catch (Exception e) {
@@ -112,8 +111,7 @@ private Map<String, Object> createJsonSchemaDefinition(Class<?> definitionClass)
     Map<String, Object> properties = new LinkedHashMap<>();
     List<String> required = new ArrayList<>();
 
-    Reflections reflections =
-        InjectorProvider.getInstance().getInjector().getInstance(Reflections.class);
+    Reflections reflections = injector.getInstance(Reflections.class);
     Set<Field> definitionFields =
         reflections.getFieldsAnnotatedWith(McpJsonSchemaDefinitionProperty.class);
     List<Field> fields =
