feat: Implement tool configuration loading

core/src/main/java/com/google/adk/agents/LlmAgent.java

@@ -39,6 +39,7 @@
 import com.google.adk.agents.Callbacks.BeforeToolCallback;
 import com.google.adk.agents.Callbacks.BeforeToolCallbackBase;
 import com.google.adk.agents.Callbacks.BeforeToolCallbackSync;
+import com.google.adk.agents.ConfigAgentUtils.ConfigurationException;
 import com.google.adk.events.Event;
 import com.google.adk.examples.BaseExampleProvider;
 import com.google.adk.examples.Example;
@@ -49,7 +50,9 @@
 import com.google.adk.models.LlmRegistry;
 import com.google.adk.models.Model;
 import com.google.adk.tools.BaseTool;
+import com.google.adk.tools.BaseTool.ToolConfig;
 import com.google.adk.tools.BaseToolset;
+import com.google.common.base.CaseFormat;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
@@ -59,6 +62,7 @@
 import io.reactivex.rxjava3.core.Flowable;
 import io.reactivex.rxjava3.core.Maybe;
 import io.reactivex.rxjava3.core.Single;
+import java.lang.reflect.Constructor;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
@@ -864,20 +868,20 @@ private Model resolveModelInternal() {
    * @param configAbsPath The absolute path to the agent config file. This is needed for resolving
    *     relative paths for e.g. tools.
    * @return the configured LlmAgent
-   * @throws ConfigAgentUtils.ConfigurationException if the configuration is invalid
+   * @throws ConfigurationException if the configuration is invalid
    *     <p>TODO: Config agent features are not yet ready for public use.
    */
   public static LlmAgent fromConfig(LlmAgentConfig config, String configAbsPath)
-      throws ConfigAgentUtils.ConfigurationException {
+      throws ConfigurationException {
     logger.debug("Creating LlmAgent from config: {}", config.name());
 
     // Validate required fields
     if (config.name() == null || config.name().trim().isEmpty()) {
-      throw new ConfigAgentUtils.ConfigurationException("Agent name is required");
+      throw new ConfigurationException("Agent name is required");
     }
 
     if (config.instruction() == null || config.instruction().trim().isEmpty()) {
-      throw new ConfigAgentUtils.ConfigurationException("Agent instruction is required");
+      throw new ConfigurationException("Agent instruction is required");
     }
 
     // Create builder with required fields
@@ -891,6 +895,14 @@ public static LlmAgent fromConfig(LlmAgentConfig config, String configAbsPath)
       builder.model(config.model());
     }
 
+    try {
+      if (config.tools() != null) {
+        builder.tools(resolveTools(config.tools(), configAbsPath));
+      }
+    } catch (ConfigurationException e) {
+      throw new ConfigurationException("Error resolving tools for agent " + config.name(), e);
+    }
+
     // Set optional transfer configuration
     if (config.disallowTransferToParent() != null) {
       builder.disallowTransferToParent(config.disallowTransferToParent());
@@ -911,4 +923,116 @@ public static LlmAgent fromConfig(LlmAgentConfig config, String configAbsPath)
 
     return agent;
   }
+
+  private static ImmutableList<BaseTool> resolveTools(
+      List<ToolConfig> toolConfigs, String configAbsPath) throws ConfigurationException {
+
+    if (toolConfigs == null || toolConfigs.isEmpty()) {
+      return ImmutableList.of();
+    }
+
+    List<BaseTool> resolvedTools = new ArrayList<>();
+
+    for (ToolConfig toolConfig : toolConfigs) {
+      try {
+        String toolName = toolConfig.name();
+        if (toolName == null || toolName.trim().isEmpty()) {
+          throw new ConfigurationException("Tool name cannot be empty");
+        }
+
+        toolName = toolName.trim();
+        BaseTool tool;
+
+        if (!toolName.contains(".")) {
+          tool = resolveBuiltInTool(toolName, toolConfig);
+        } else {
+          // TODO: Support user-defined tools
+          logger.debug("configAbsPath is: {}", configAbsPath);
+          throw new ConfigurationException("User-defined tools are not yet supported");
+        }
+
+        resolvedTools.add(tool);
+        logger.debug("Successfully resolved tool: {}", toolConfig.name());
+      } catch (Exception e) {
+        String errorMsg = "Failed to resolve tool: " + toolConfig.name();
+        logger.error(errorMsg, e);
+        throw new ConfigurationException(errorMsg, e);
+      }
+    }
+
+    return ImmutableList.copyOf(resolvedTools);
+  }
+
+  private static BaseTool resolveBuiltInTool(String toolName, ToolConfig toolConfig)
+      throws ConfigurationException {
+    try {
+      logger.debug("Resolving built-in tool: {}", toolName);
+      // TODO: Handle built-in tool name end with Tool while config yaml file does not.
+      // e.g.google_search in config yaml file and GoogleSearchTool in tool class name.
+      String pascalCaseToolName = CaseFormat.LOWER_UNDERSCORE.to(CaseFormat.UPPER_CAMEL, toolName);
+      String className = "com.google.adk.tools." + pascalCaseToolName;
+      Class<?> toolClass;
+      try {
+        toolClass = Class.forName(className);
+        logger.debug("Successfully loaded tool class: {}", className);
+      } catch (ClassNotFoundException e) {
+        String fallbackClassName = "com.google.adk.tools." + toolName;
+        try {
+          toolClass = Class.forName(fallbackClassName);
+        } catch (ClassNotFoundException e2) {
+          throw new ConfigurationException(
+              "Built-in tool not found: "
+                  + toolName
+                  + ". Expected class: "
+                  + className
+                  + " or "
+                  + fallbackClassName,
+              e2);
+        }
+      }
+
+      if (!BaseTool.class.isAssignableFrom(toolClass)) {
+        throw new ConfigurationException(
+            "Built-in tool class " + toolClass.getName() + " does not extend BaseTool");
+      }
+
+      @SuppressWarnings("unchecked")
+      Class<? extends BaseTool> baseToolClass = (Class<? extends BaseTool>) toolClass;
+
+      BaseTool tool = createToolInstance(baseToolClass, toolConfig);
+      logger.info(
+          "Successfully created built-in tool: {} (class: {})", toolName, toolClass.getName());
+
+      return tool;
+
+    } catch (Exception e) {
+      logger.error("Failed to create built-in tool: {}", toolName, e);
+      throw new ConfigurationException("Failed to create built-in tool: " + toolName, e);
+    }
+  }
+
+  private static BaseTool createToolInstance(
+      Class<? extends BaseTool> toolClass, ToolConfig toolConfig)
+      throws ConfigAgentUtils.ConfigurationException {
+
+    try {
+      // TODO:implement constructor with ToolArgsConfig
+      logger.debug("ToolConfig is: {}", toolConfig);
+
+      // Try default constructor
+      try {
+        Constructor<? extends BaseTool> constructor = toolClass.getConstructor();
+        return constructor.newInstance();
+      } catch (NoSuchMethodException e) {
+        // Continue
+      }
+
+      throw new ConfigAgentUtils.ConfigurationException(
+          "No suitable constructor found for tool class: " + toolClass.getName());
+
+    } catch (Exception e) {
+      throw new ConfigAgentUtils.ConfigurationException(
+          "Failed to instantiate tool class: " + toolClass.getName(), e);
+    }
+  }
 }

core/src/main/java/com/google/adk/agents/LlmAgentConfig.java

@@ -17,6 +17,8 @@
 package com.google.adk.agents;
 
 import com.fasterxml.jackson.annotation.JsonProperty;
+import com.google.adk.tools.BaseTool.ToolConfig;
+import java.util.List;
 
 /**
  * Configuration for LlmAgent.
@@ -29,6 +31,7 @@ public class LlmAgentConfig extends BaseAgentConfig {
   private Boolean disallowTransferToParent;
   private Boolean disallowTransferToPeers;
   private String outputKey;
+  private List<ToolConfig> tools;
 
   public LlmAgentConfig() {
     super();
@@ -80,4 +83,13 @@ public String outputKey() {
   public void setOutputKey(String outputKey) {
     this.outputKey = outputKey;
   }
+
+  @JsonProperty("tools")
+  public List<ToolConfig> tools() {
+    return tools;
+  }
+
+  public void setTools(List<ToolConfig> tools) {
+    this.tools = tools;
+  }
 }

core/src/main/java/com/google/adk/tools/BaseTool.java

@@ -18,15 +18,20 @@
 
 import static com.google.common.collect.ImmutableList.toImmutableList;
 
+import com.fasterxml.jackson.annotation.JsonIgnore;
+import com.google.adk.JsonBaseModel;
+import com.google.adk.agents.ConfigAgentUtils.ConfigurationException;
 import com.google.adk.models.LlmRequest;
 import com.google.common.collect.ImmutableList;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
+import com.google.errorprone.annotations.DoNotCall;
 import com.google.genai.types.FunctionDeclaration;
 import com.google.genai.types.GenerateContentConfig;
 import com.google.genai.types.LiveConnectConfig;
 import com.google.genai.types.Tool;
 import io.reactivex.rxjava3.core.Completable;
 import io.reactivex.rxjava3.core.Single;
+import java.util.HashMap;
 import java.util.Map;
 import java.util.Optional;
 import javax.annotation.Nonnull;
@@ -156,4 +161,66 @@ private static ImmutableList<Tool> findToolsWithoutFunctionDeclarations(LlmReque
                     .collect(toImmutableList()))
         .orElse(ImmutableList.of());
   }
+
+  /**
+   * Creates a tool instance from a config.
+   *
+   * <p>Subclasses should override and implement this method to do custom initialization from a
+   * config.
+   *
+   * @param config The config for the tool.
+   * @param configAbsPath The absolute path to the config file that contains the tool config.
+   * @return The tool instance.
+   * @throws ConfigurationException if the tool cannot be created from the config.
+   */
+  @DoNotCall("Always throws com.google.adk.agents.ConfigAgentUtils.ConfigurationException")
+  public static BaseTool fromConfig(ToolConfig config, String configAbsPath)
+      throws ConfigurationException {
+    throw new ConfigurationException(
+        "fromConfig not implemented for " + BaseTool.class.getSimpleName());
+  }
+
+  /** Configuration class for tool arguments that allows arbitrary key-value pairs. */
+  // TODO implement this class
+  public static class ToolArgsConfig extends JsonBaseModel {
+
+    @JsonIgnore private final Map<String, Object> additionalProperties = new HashMap<>();
+
+    public boolean isEmpty() {
+      return additionalProperties.isEmpty();
+    }
+
+    public int size() {
+      return additionalProperties.size();
+    }
+  }
+
+  /** Configuration class for a tool definition in YAML/JSON. */
+  public static class ToolConfig extends JsonBaseModel {
+    private String name;
+    private ToolArgsConfig args;
+
+    public ToolConfig() {}
+
+    public ToolConfig(String name, ToolArgsConfig args) {
+      this.name = name;
+      this.args = args;
+    }
+
+    public String name() {
+      return name;
+    }
+
+    public void setName(String name) {
+      this.name = name;
+    }
+
+    public ToolArgsConfig args() {
+      return args;
+    }
+
+    public void setArgs(ToolArgsConfig args) {
+      this.args = args;
+    }
+  }
 }

core/src/test/java/com/google/adk/agents/ConfigAgentUtilsTest.java

@@ -219,6 +219,55 @@ public void fromConfig_withEmptyModel_doesNotSetModelOnAgent()
     assertThat(llmAgent.model()).isEmpty();
   }
 
+  @Test
+  public void fromConfig_withBuiltInTool_loadsTool() throws IOException, ConfigurationException {
+    File configFile = tempFolder.newFile("with_tool.yaml");
+    Files.writeString(
+        configFile.toPath(),
+        """
+        name: search_agent
+        model: gemini-1.5-flash
+        description: 'an agent whose job it is to perform Google search queries and answer questions about the results.'
+        instruction: You are an agent whose job is to perform Google search queries and answer questions about the results.
+        agent_class: LlmAgent
+        tools:
+          - name: GoogleSearchTool
+        """);
+    String configPath = configFile.getAbsolutePath();
+
+    BaseAgent agent = ConfigAgentUtils.fromConfig(configPath);
+
+    assertThat(agent).isInstanceOf(LlmAgent.class);
+    LlmAgent llmAgent = (LlmAgent) agent;
+    assertThat(llmAgent.tools()).hasSize(1);
+    assertThat(llmAgent.tools().get(0).name()).isEqualTo("google_search");
+  }
+
+  @Test
+  public void fromConfig_withBuiltInTool_loadsToolWithUnderscore()
+      throws IOException, ConfigurationException {
+    File configFile = tempFolder.newFile("with_tool_underscore.yaml");
+    Files.writeString(
+        configFile.toPath(),
+        """
+        name: search_agent
+        model: gemini-1.5-flash
+        description: 'an agent whose job it is to perform Google search queries and answer questions about the results.'
+        instruction: You are an agent whose job is to perform Google search queries and answer questions about the results.
+        agent_class: LlmAgent
+        tools:
+          - name: google_search_tool
+        """);
+    String configPath = configFile.getAbsolutePath();
+
+    BaseAgent agent = ConfigAgentUtils.fromConfig(configPath);
+
+    assertThat(agent).isInstanceOf(LlmAgent.class);
+    LlmAgent llmAgent = (LlmAgent) agent;
+    assertThat(llmAgent.tools()).hasSize(1);
+    assertThat(llmAgent.tools().get(0).name()).isEqualTo("google_search");
+  }
+
   @Test
   public void fromConfig_withInvalidModel_throwsExceptionOnModelResolution()
       throws IOException, ConfigurationException {