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<li><a href="#injectSessionState(com.google.adk.agents.InvocationContext,java.lang.String)" tabindex="0">injectSessionState(InvocationContext, String)</a></li>
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<h1 title="Class InstructionUtils" class="title">Class InstructionUtils</h1>
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<div class="inheritance" title="Inheritance Tree"><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html" title="class in java.lang" class="external-link">java.lang.Object</a>
<div class="inheritance">com.google.adk.utils.InstructionUtils</div>
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<div class="type-signature"><span class="modifiers">public final class </span><span class="element-name type-name-label">InstructionUtils</span>
<span class="extends-implements">extends <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html" title="class in java.lang" class="external-link">Object</a></span></div>
<div class="block">Utility methods for handling instruction templates.</div>
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<h2>Method Summary</h2>
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<div class="table-header col-last">Description</div>
<div class="col-first even-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4"><code>static io.reactivex.rxjava3.core.Single<wbr>&lt;<a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html" title="class in java.lang" class="external-link">String</a>&gt;</code></div>
<div class="col-second even-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4"><code><a href="#injectSessionState(com.google.adk.agents.InvocationContext,java.lang.String)" class="member-name-link">injectSessionState</a><wbr>(<a href="../agents/InvocationContext.html" title="class in com.google.adk.agents">InvocationContext</a>&nbsp;context,
 <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html" title="class in java.lang" class="external-link">String</a>&nbsp;template)</code></div>
<div class="col-last even-row-color method-summary-table method-summary-table-tab1 method-summary-table-tab4">
<div class="block">Populates placeholders in an instruction template string with values from the session state or
loaded artifacts.</div>
</div>
</div>
</div>
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<h3 id="methods-inherited-from-class-java.lang.Object">Methods inherited from class&nbsp;<a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#method-summary" title="class in java.lang" class="external-link">Object</a></h3>
<code><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#clone()" title="clone()" class="external-link">clone</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#equals(java.lang.Object)" title="equals(Object)" class="external-link">equals</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#finalize()" title="finalize()" class="external-link">finalize</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#getClass()" title="getClass()" class="external-link">getClass</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#hashCode()" title="hashCode()" class="external-link">hashCode</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#notify()" title="notify()" class="external-link">notify</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#notifyAll()" title="notifyAll()" class="external-link">notifyAll</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#toString()" title="toString()" class="external-link">toString</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#wait()" title="wait()" class="external-link">wait</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#wait(long)" title="wait(long)" class="external-link">wait</a>, <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/Object.html#wait(long,int)" title="wait(long, int)" class="external-link">wait</a></code></div>
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<h2>Method Details</h2>
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<section class="detail" id="injectSessionState(com.google.adk.agents.InvocationContext,java.lang.String)">
<h3>injectSessionState</h3>
<div class="horizontal-scroll">
<div class="member-signature"><span class="modifiers">public static</span>&nbsp;<span class="return-type">io.reactivex.rxjava3.core.Single&lt;<a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html" title="class in java.lang" class="external-link">String</a>&gt;</span>&nbsp;<span class="element-name">injectSessionState</span><wbr><span class="parameters">(<a href="../agents/InvocationContext.html" title="class in com.google.adk.agents">InvocationContext</a>&nbsp;context,
 <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html" title="class in java.lang" class="external-link">String</a>&nbsp;template)</span></div>
<div class="block">Populates placeholders in an instruction template string with values from the session state or
loaded artifacts.

<p><b>Placeholder Syntax:</b>

<p>Placeholders are enclosed by one or more curly braces at the start and end, e.g., <code>
{key}</code> or <code>{{key}}</code>. The core <code>key</code> is extracted from whatever is between the
innermost pair of braces after trimming whitespace and possibly removing the <code>?</code> which
denotes optionality (e.g. <code>{key?}</code>). The <code>key</code> itself must not contain curly
braces. For typical usage, a single pair of braces like <code>{my_variable}</code> is standard.

<p>The extracted <code>key</code> determines the source and name of the value:

<ul>
  <li><b>Session State Variables:</b> The <code>key</code> (e.g., <code>"variable_name"</code> or <code>
      "prefix:variable_name"</code>) refers to a variable in session state.
      <ul>
        <li>Simple name: <code>{variable_name}</code>. The <code>variable_name</code> part must be a
            valid identifier as per <code>isValidStateName(String)</code>. Invalid names will
            result in the placeholder being returned as is.
        <li>Prefixed name: <code>{prefix:variable_name}</code>. Valid prefixes are: <a href="../sessions/State.html#APP_PREFIX">"app:"</a>, <a href="../sessions/State.html#USER_PREFIX">"user:"</a>, and <a href="../sessions/State.html#TEMP_PREFIX">"temp:"</a> The part of the name following the
            prefix must also be a valid identifier. Invalid prefixes will result in the
            placeholder being returned as is.
      </ul>
  <li><b>Artifacts:</b> The <code>key</code> starts with "<code>artifact.</code>" (e.g., <code>
      "artifact.file_name"</code>).
  <li><b>Optional Placeholders:</b> A <code>key</code> can be marked as optional by appending a
      question mark <code>?</code> at its very end, inside the braces.
      <ul>
        <li>Example: <code>{optional_variable?}</code>, <code>{{artifact.optional_file.txt?}}</code>
        <li>If an optional placeholder cannot be resolved (e.g., variable not found, artifact
            not found), it is replaced with an empty string.
      </ul>
</ul>

<b>Example Usage:</b>

<pre><code>InvocationContext context = ...; // Assume this is initialized with session and artifact service
Session session = context.session();

session.state().put("user:name", "Alice");

context.artifactService().saveArtifact(
    session.appName(), session.userId(), session.id(), "knowledge.txt", Part.fromText("Origins of the universe: At first, there was-"));

String template = "You are {user:name}'s assistant. Answer questions based on your knowledge. Your knowledge: {artifact.knowledge.txt}." +
                  " Your extra knowledge: {artifact.missing_artifact.txt?}";

Single&lt;String&gt; populatedStringSingle = InstructionUtils.injectSessionState(context, template);
populatedStringSingle.subscribe(
    result -&gt; System.out.println(result),
    // Expected: "You are Alice's assistant. Answer questions based on your knowledge. Your knowledge: Origins of the universe: At first, there was-. Your extra knowledge: "
    error -&gt; System.err.println("Error populating template: " + error.getMessage())
);
</code></pre></div>
<dl class="notes">
<dt>Parameters:</dt>
<dd><code>context</code> - The invocation context providing access to session state and artifact services.</dd>
<dd><code>template</code> - The instruction template string containing placeholders to be populated.</dd>
<dt>Returns:</dt>
<dd>A <code>Single</code> that will emit the populated instruction string upon successful
    resolution of all non-optional placeholders. Emits the original template if it is empty or
    contains no placeholders that are processed.</dd>
<dt>Throws:</dt>
<dd><code><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/NullPointerException.html" title="class in java.lang" class="external-link">NullPointerException</a></code> - if the template or context is null.</dd>
<dd><code><a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/IllegalArgumentException.html" title="class in java.lang" class="external-link">IllegalArgumentException</a></code> - if a non-optional variable or artifact is not found.</dd>
</dl>
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