Class ContextFilterPlugin

java.lang.Object

com.google.adk.plugins.BasePlugin

com.google.adk.plugins.ContextFilterPlugin

All Implemented Interfaces:

Plugin

public class ContextFilterPlugin
extends BasePlugin

A plugin that filters the LLM request Content list to reduce its size, for example to adhere to context window limits.

This plugin can be configured to trim the conversation history based on one or both of the following criteria:

• numInvocationsToKeep(N): Retains only the last N model turns and any preceding user turns. If multiple user messages appear consecutively before a model message, all of them are kept as part of that model invocation window.
• customFilter(): Applies a custom UnaryOperator to filter the list of Content objects. If numInvocationsToKeep is also specified, the custom filter is applied after the invocation-based trimming occurs.

Function Call Handling: The plugin ensures that if a FunctionResponse is included in the filtered list, its corresponding FunctionCall is also included. If filtering would otherwise exclude the FunctionCall, the window is automatically expanded to include it, preventing orphaned function responses.

If no filtering options are provided, this plugin has no effect. If the customFilter throws an exception during execution, filtering is aborted, and the LlmRequest is not modified.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	ContextFilterPlugin.Builder	Builder for ContextFilterPlugin.

Field Summary

Fields inherited from class BasePlugin

name

Modifier and Type	Field	Description
protected final String	name

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	ContextFilterPlugin(ContextFilterPlugin.Builder builder)

Method Summary

Modifier and Type	Method	Description
io.reactivex.rxjava3.core.Maybe<LlmResponse>	beforeModelCallback(CallbackContext callbackContext, LlmRequest.Builder llmRequest)	Filters the LLM request context by trimming recent turns and applying any custom filter.
static ContextFilterPlugin.Builder	builder()

Methods inherited from class BasePlugin

getName

Modifier and Type	Method	Description
String	getName()

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface Plugin

afterAgentCallback, afterModelCallback, afterRunCallback, afterToolCallback, beforeAgentCallback, beforeRunCallback, beforeToolCallback, close, onEventCallback, onModelErrorCallback, onToolErrorCallback, onUserMessageCallback

Modifier and Type	Method	Description
default io.reactivex.rxjava3.core.Maybe<com.google.genai.types.Content>	afterAgentCallback(BaseAgent agent, CallbackContext callbackContext)	Callback executed after an agent's primary logic has completed.
default io.reactivex.rxjava3.core.Maybe<LlmResponse>	afterModelCallback(CallbackContext callbackContext, LlmResponse llmResponse)	Callback executed after a response is received from the model.
default io.reactivex.rxjava3.core.Completable	afterRunCallback(InvocationContext invocationContext)	Callback executed after an ADK runner run has completed.
default io.reactivex.rxjava3.core.Maybe<Map<String,Object>>	afterToolCallback(BaseTool tool, Map<String,Object> toolArgs, ToolContext toolContext, Map<String,Object> result)	Callback executed after a tool has been called.
default io.reactivex.rxjava3.core.Maybe<com.google.genai.types.Content>	beforeAgentCallback(BaseAgent agent, CallbackContext callbackContext)	Callback executed before an agent's primary logic is invoked.
default io.reactivex.rxjava3.core.Maybe<com.google.genai.types.Content>	beforeRunCallback(InvocationContext invocationContext)	Callback executed before the ADK runner runs.
default io.reactivex.rxjava3.core.Maybe<Map<String,Object>>	beforeToolCallback(BaseTool tool, Map<String,Object> toolArgs, ToolContext toolContext)	Callback executed before a tool is called.
default io.reactivex.rxjava3.core.Completable	close()	Method executed when the runner is closed.
default io.reactivex.rxjava3.core.Maybe<Event>	onEventCallback(InvocationContext invocationContext, Event event)	Callback executed after an event is yielded from runner.
default io.reactivex.rxjava3.core.Maybe<LlmResponse>	onModelErrorCallback(CallbackContext callbackContext, LlmRequest.Builder llmRequest, Throwable error)	Callback executed when a model call encounters an error.
default io.reactivex.rxjava3.core.Maybe<Map<String,Object>>	onToolErrorCallback(BaseTool tool, Map<String,Object> toolArgs, ToolContext toolContext, Throwable error)	Callback executed when a tool call encounters an error.
default io.reactivex.rxjava3.core.Maybe<com.google.genai.types.Content>	onUserMessageCallback(InvocationContext invocationContext, com.google.genai.types.Content userMessage)	Callback executed when a user message is received before an invocation starts.

Constructor Details

ContextFilterPlugin

protected ContextFilterPlugin(ContextFilterPlugin.Builder builder)

Method Details

builder

public static ContextFilterPlugin.Builder builder()

beforeModelCallback

public io.reactivex.rxjava3.core.Maybe<LlmResponse> beforeModelCallback(CallbackContext callbackContext,
 LlmRequest.Builder llmRequest)

Filters the LLM request context by trimming recent turns and applying any custom filter.

If numInvocationsToKeep is set, this method retains only the most recent model turns and their preceding user turns. It ensures that function calls and responses remain paired. If a customFilter is provided, it is applied to the list after trimming.

Parameters:

callbackContext - The context of the callback.

llmRequest - The request builder whose contents will be updated in place.

Returns:

Maybe.empty() as this plugin only modifies the request builder.