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_flash_advanced_handler-default-implementations" data-v-e6f2a212><div><h1 id="⚡-handler-default-implementations-hdi" tabindex="-1">⚡ Handler Default Implementations (HDI) <a class="header-anchor" href="#⚡-handler-default-implementations-hdi" aria-label="Permalink to &quot;⚡ Handler Default Implementations (HDI)&quot;">​</a></h1><p>Handler Default Implementations (HDIs) offer a streamlined approach to standardize common behaviors across request handlers in Flash. By extending a base <code>RequestHandler</code> (or chaining multiple base handlers), you can centralize tasks like authentication, user data retrieval, and rate limiting while keeping your code modular and maintainable.</p><p>HDIs use the <a href="https://en.wikipedia.org/wiki/Chain-of-responsibility_pattern" target="_blank" rel="noreferrer">Chain of Responsibility pattern</a> to layer reusable logic, ensuring that shared functionality is defined once and inherited by all handlers.</p><p><img src="/assets/hdi.CNuX0-qb.png" alt="HDI"></p><h2 id="🔗-how-hdis-work" tabindex="-1">🔗 How HDIs Work <a class="header-anchor" href="#🔗-how-hdis-work" aria-label="Permalink to &quot;🔗 How HDIs Work&quot;">​</a></h2><p>Rather than repeating common logic across different handlers, HDIs allow you to create <strong>abstract base handlers</strong> that encapsulate shared behaviors. When your individual request handlers extend these bases, they automatically inherit predefined functionality, and you only need to implement request-specific logic.</p><h3 id="key-benefits" tabindex="-1">Key Benefits <a class="header-anchor" href="#key-benefits" aria-label="Permalink to &quot;Key Benefits&quot;">​</a></h3><ul><li><p><strong>Build-Time Optimization:</strong><br> When your project is compiled, Flash’s router merges the entire HDI chain into a single handler instance. This eliminates extra function calls and runtime lookups, resulting in a leaner execution path compared to traditional middleware stacks.</p></li><li><p><strong>Reduced Complexity:</strong><br> Unlike frameworks that rely on reflection (e.g., Spring Boot) or a deep middleware stack (e.g., Express.js), HDIs embed inherited behavior directly in the compiled class, minimizing runtime overhead.</p></li><li><p><strong>Type Safety &amp; Clean State Management:</strong><br> Protected fields in HDIs allow seamless data sharing between handlers without using global variables, callbacks, or type casting. Note: Always declare these fields as instance (non-static) variables to ensure each handler maintains its own state.</p></li></ul><h2 id="🛡️-hdi-design-guidelines" tabindex="-1">🛡️ HDI Design Guidelines <a class="header-anchor" href="#🛡️-hdi-design-guidelines" aria-label="Permalink to &quot;🛡️ HDI Design Guidelines&quot;">​</a></h2><h3 id="_1-base-hdi-class" tabindex="-1">1. Base HDI Class <a class="header-anchor" href="#_1-base-hdi-class" aria-label="Permalink to &quot;1. Base HDI Class&quot;">​</a></h3><p>Define an abstract base class that extends <code>RequestHandler</code> to encapsulate common logic:</p><ul><li><p><strong>Constructor:</strong><br> Initialize by passing <code>Request</code> and <code>Response</code> objects to the superclass.</p></li><li><p><strong>Overridden <code>handle</code> Method:</strong><br> Implement common logic and delegate to an abstract method for custom behavior.</p><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">@</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">Override</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">public</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> Object </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">handle</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // Insert common logic here (e.g., logging, header processing)</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> handleCustom</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre></div></li><li><p><strong>Abstract Method:</strong><br> Declare an abstract method that must be implemented by subclasses.</p><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">protected</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> abstract</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> Object </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">handleCustom</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span></code></pre></div></li><li><p><strong>Protected Fields:</strong><br> Use protected instance fields to share data between HDI layers.</p><blockquote><p><strong>Warning:</strong> Do <strong>not</strong> declare these fields as static. Each handler should manage its own state.</p><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// Incorrect: static field</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">protected</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> static</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> String data;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;">// Correct: instance field</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">protected</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> String data;</span></span></code></pre></div></blockquote></li></ul><h3 id="_2-concrete-handler-implementation" tabindex="-1">2. Concrete Handler Implementation <a class="header-anchor" href="#_2-concrete-handler-implementation" aria-label="Permalink to &quot;2. Concrete Handler Implementation&quot;">​</a></h3><p>Extend the base HDI class in your handler:</p><ul><li><p><strong>Constructor:</strong><br> Call the super constructor with the necessary <code>Request</code> and <code>Response</code> objects.</p></li><li><p><strong>Implement <code>handleCustom()</code>:</strong><br> Write the request-specific logic here. Protected fields from the base class are available within this method.</p><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">@</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">Override</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">protected</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> Object </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">handleCustom</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // Custom logic using inherited data</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;Response&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre></div></li></ul><h2 id="🛠️-example-api-key-authentication" tabindex="-1">🛠️ Example: API Key Authentication <a class="header-anchor" href="#🛠️-example-api-key-authentication" aria-label="Permalink to &quot;🛠️ Example: API Key Authentication&quot;">​</a></h2><p>This example demonstrates how to build an HDI that validates an API key before processing a request.</p><h3 id="abstract-api-key-protected-handler" tabindex="-1">Abstract API Key Protected Handler <a class="header-anchor" href="#abstract-api-key-protected-handler" aria-label="Permalink to &quot;Abstract API Key Protected Handler&quot;">​</a></h3><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">public</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> abstract</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> class</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> APIKeyProtectedHandler</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> extends</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> RequestHandler</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> protected</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> String apiKey;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> public</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> APIKeyProtectedHandler</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(Request </span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70;">req</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, Response </span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70;">res</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) {</span></span>
<span class="line"><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> super</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(req, res);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> @</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">Override</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> public</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> Object </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">handle</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> apiKey </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> req.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">header</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;X-API-Key&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> if</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (apiKey </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">==</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> null</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> ||</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> !</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">isValidApiKey</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(apiKey)) {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> res.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">status</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">403</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> res.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">type</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;application/json&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;{</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">error</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">Invalid API Key</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> handleAuthorized</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> protected</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> abstract</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> Object </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">handleAuthorized</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> private</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> boolean</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> isValidApiKey</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(String </span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70;">key</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) {</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // Implement your API key validation logic here</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> true</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre></div><h3 id="concrete-api-handler" tabindex="-1">Concrete API Handler <a class="header-anchor" href="#concrete-api-handler" aria-label="Permalink to &quot;Concrete API Handler&quot;">​</a></h3><p>Extend the abstract handler to process the request only if the API key is valid:</p><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">@</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">RouteInfo</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">endpoint</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;/data&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">method</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> HttpMethod.GET)</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">public</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> class</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> GetDataHandler</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> extends</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> APIKeyProtectedHandler</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> public</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> GetDataHandler</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(Request </span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70;">req</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, Response </span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70;">res</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) {</span></span>
<span class="line"><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> super</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(req, res);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> @</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">Override</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> protected</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> Object </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">handleAuthorized</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> res.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">type</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;application/json&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;{</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">data</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">Your API response here</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre></div><h2 id="🏗️-chaining-hdis-for-modular-logic" tabindex="-1">🏗️ Chaining HDIs for Modular Logic <a class="header-anchor" href="#🏗️-chaining-hdis-for-modular-logic" aria-label="Permalink to &quot;🏗️ Chaining HDIs for Modular Logic&quot;">​</a></h2><p>HDIs can be layered to build complex flows. For instance, you might first authenticate a request, then fetch user data.</p><h3 id="protected-handler-authentication" tabindex="-1">Protected Handler (Authentication) <a class="header-anchor" href="#protected-handler-authentication" aria-label="Permalink to &quot;Protected Handler (Authentication)&quot;">​</a></h3><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">public</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> abstract</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> class</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> ProtectedHandler</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> extends</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> RequestHandler</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> protected</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> String authToken;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> public</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> ProtectedHandler</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(Request </span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70;">req</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, Response </span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70;">res</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) {</span></span>
<span class="line"><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> super</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(req, res);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> @</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">Override</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> public</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> Object </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">handle</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> authToken </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> req.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">header</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;Authorization&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> if</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (authToken </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">==</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> null</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> ||</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> !</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">isValidToken</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(authToken)) {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> res.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">status</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">401</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> res.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">type</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;application/json&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;{</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">error</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">Unauthorized</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> handleAuthenticated</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> protected</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> abstract</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> Object </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">handleAuthenticated</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> private</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> boolean</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> isValidToken</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(String </span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70;">token</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) {</span></span>
<span class="line"><span style="--shiki-light:#6A737D;--shiki-dark:#6A737D;"> // Validate the token here</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> true</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre></div><h3 id="authenticated-handler-user-data-retrieval" tabindex="-1">Authenticated Handler (User Data Retrieval) <a class="header-anchor" href="#authenticated-handler-user-data-retrieval" aria-label="Permalink to &quot;Authenticated Handler (User Data Retrieval)&quot;">​</a></h3><p>Extend the <code>ProtectedHandler</code> to fetch user details:</p><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">public</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> abstract</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> class</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> AuthenticatedHandler</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> extends</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> ProtectedHandler</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> protected</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> User user;</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> public</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> AuthenticatedHandler</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(Request </span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70;">req</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, Response </span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70;">res</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) {</span></span>
<span class="line"><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> super</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(req, res);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> @</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">Override</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> protected</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> Object </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">handleAuthenticated</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> user </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">=</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> getUserFromDatabase</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(authToken);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> if</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> (user </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">==</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> null</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> res.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">status</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">403</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> res.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">type</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;application/json&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;{</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">error</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">User not found</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> handleWithUser</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> protected</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> abstract</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> Object </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">handleWithUser</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">();</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre></div><h3 id="final-handler-implementation" tabindex="-1">Final Handler Implementation <a class="header-anchor" href="#final-handler-implementation" aria-label="Permalink to &quot;Final Handler Implementation&quot;">​</a></h3><p>Implement the final handler that uses the authenticated user data:</p><div class="language-java vp-adaptive-theme"><button title="Copy Code" class="copy"></button><span class="lang">java</span><pre class="shiki shiki-themes github-light github-dark vp-code" tabindex="0"><code><span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">@</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">RouteInfo</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">endpoint</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;/profile&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, </span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">method</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> =</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> HttpMethod.GET)</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">public</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> class</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> UserProfileHandler</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> extends</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> AuthenticatedHandler</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> {</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> public</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;"> UserProfileHandler</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(Request </span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70;">req</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">, Response </span><span style="--shiki-light:#E36209;--shiki-dark:#FFAB70;">res</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">) {</span></span>
<span class="line"><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;"> super</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(req, res);</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> @</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">Override</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> protected</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> Object </span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">handleWithUser</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() {</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> res.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">type</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">(</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;application/json&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">);</span></span>
<span class="line"><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> return</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;{</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">username</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">:</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">&quot;</span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;"> +</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> user.</span><span style="--shiki-light:#6F42C1;--shiki-dark:#B392F0;">getUsername</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">() </span><span style="--shiki-light:#D73A49;--shiki-dark:#F97583;">+</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;"> &quot;</span><span style="--shiki-light:#005CC5;--shiki-dark:#79B8FF;">\&quot;</span><span style="--shiki-light:#032F62;--shiki-dark:#9ECBFF;">}&quot;</span><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">;</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;"> }</span></span>
<span class="line"><span style="--shiki-light:#24292E;--shiki-dark:#E1E4E8;">}</span></span></code></pre></div><hr><p>For reference, here&#39;s a visual representation of how an HDI chain operates: <br></p><p><img src="/assets/hdichain.FX-X2Mhu.png" alt="HDI Chain"></p></div></div></main><footer class="VPDocFooter" data-v-e6f2a212 data-v-1bcd8184><!--[--><!--]--><!----><nav class="prev-next" aria-labelledby="doc-footer-aria-label" data-v-1bcd8184><span class="visually-hidden" id="doc-footer-aria-label" data-v-1bcd8184>Pager</span><div class="pager" data-v-1bcd8184><a class="VPLink link pager-link prev" href="/flash/file-serving/dynamic-file-server.html" data-v-1bcd8184><!--[--><span class="desc" data-v-1bcd8184>Previous page</span><span class="title" data-v-1bcd8184>Dynamic Files Server</span><!--]--></a></div><div class="pager" data-v-1bcd8184><a class="VPLink link pager-link next" href="/flash/advanced/fullstack-development.html" data-v-1bcd8184><!--[--><span class="desc" data-v-1bcd8184>Next page</span><span class="title" data-v-1bcd8184>Fullstack Development</span><!--]--></a></div></nav></footer><!--[--><!--]--></div></div></div><!--[--><!--]--></div></div><!----><!--[--><!--]--></div></div>
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