| The schema instance defines the schema for the data being produced using the producer instance. Take Avro as an example, Pulsar extracts the schema definition from the POJO class and constructs the <code>SchemaInfo</code>.</p></li><li><p>The producer requests to connect to the broker with the <code>SchemaInfo</code> extracted from the passed-in schema instance.</p></li><li><p>The broker looks up the schema registry to check if it is a registered schema.</p><ul><li>If the schema is registered, the broker returns the schema version to the producer.</li><li>Otherwise, go to step 4.</li></ul></li><li><p>The broker checks whether the schema can be auto-updated.</p><ul><li>If it's not allowed to be auto-updated, then the schema cannot be registered, and the broker rejects the producer.</li><li>Otherwise, go to step 5.</li></ul></li><li><p>The broker performs the <a href="/docs/3.0.x/schema-understand/#schema-compatibility-check">schema compatibility check</a> defined for the topic.</p><ul><li>If the schema passes the compatibility check, the broker stores it in the schema registry and returns the schema version to the producer. All the messages produced by this producer are tagged with the schema version.</li><li>Otherwise, the broker rejects the producer.</li></ul></li></ol><h3 class="anchor anchorWithStickyNavbar_LWe7" id="consumer-side">Consumer side<a href="#consumer-side" class="hash-link" aria-label="Direct link to Consumer side" title="Direct link to Consumer side"></a></h3><p>This diagram illustrates how schema works on the consumer side.</p><p><img loading="lazy" alt="How Pulsar schema works on the consumer side" src="/assets/images/schema-consumer-67cb670626412e11b3a683b2523cc1e8.svg" width="1548" height="908" class="img_ev3q"></p><ol><li><p>The application uses a schema instance to construct a consumer instance.</p></li><li><p>The consumer connects to the broker with the <code>SchemaInfo</code> extracted from the passed-in schema instance.</p></li><li><p>The broker checks if the topic is in use (has at least one of the objects: schema, data, active producer or consumer).</p><ul><li>If a topic has at least one of the above objects, go to step 5.</li><li>Otherwise, go to step 4.</li></ul></li><li><p>The broker checks whether the schema can be auto-updated.</p><ul><li>If the schema can be auto-updated, the broker registers the schema and connects the consumer.</li><li>Otherwise, the broker rejects the consumer.</li></ul></li><li><p>The broker performs the <a href="/docs/3.0.x/schema-understand/#schema-compatibility-check">schema compatibility check</a>.</p><ul><li>If the schema passes the compatibility check, the broker connects the consumer.</li><li>Otherwise, the broker rejects the consumer.</li></ul></li></ol><h2 class="anchor anchorWithStickyNavbar_LWe7" id="use-case">Use case<a href="#use-case" class="hash-link" aria-label="Direct link to Use case" title="Direct link to Use case"></a></h2><p>You can use language-specific types of data when constructing and handling messages from simple data types like <code>string</code> to more complex application-specific types.</p><p>For example, you are using the <em>User</em> class to define the messages sent to Pulsar topics.</p><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">public</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">class</span><span class="token plain"> </span><span class="token class-name">User</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">public</span><span class="token plain"> </span><span class="token class-name">String</span><span class="token plain"> name</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">public</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">int</span><span class="token plain"> age</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token class-name">User</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token class-name">User</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token class-name">String</span><span class="token plain"> name</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">int</span><span class="token plain"> age</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">{</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">this</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">name </span><span class="token operator">=</span><span class="token plain"> name</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">this</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">age </span><span class="token operator">=</span><span class="token plain"> age</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token punctuation" style="color:rgb(248, 248, 242)">}</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p><strong>Without a schema</strong></p><p>If you construct a producer without specifying a schema, then the producer can only produce messages of type <code>byte[]</code>. If you have a POJO class, you need to serialize the POJO into bytes before sending messages.</p><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token class-name">Producer</span><span class="token operator"><</span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">byte</span><span class="token punctuation" style="color:rgb(248, 248, 242)">[</span><span class="token punctuation" style="color:rgb(248, 248, 242)">]</span><span class="token operator">></span><span class="token plain"> producer </span><span class="token operator">=</span><span class="token plain"> client</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">newProducer</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">create</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token class-name">User</span><span class="token plain"> user </span><span class="token operator">=</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">new</span><span class="token plain"> </span><span class="token class-name">User</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token string" style="color:rgb(255, 121, 198)">"Tom"</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> </span><span class="token number">28</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">byte</span><span class="token punctuation" style="color:rgb(248, 248, 242)">[</span><span class="token punctuation" style="color:rgb(248, 248, 242)">]</span><span class="token plain"> message </span><span class="token operator">=</span><span class="token plain"> … </span><span class="token comment" style="color:rgb(98, 114, 164)">// serialize the `user` by yourself;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain">producer</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">send</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">message</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><p><strong>With a schema</strong></p><p>This example constructs a producer with the <em>JSONSchema</em>, and you can send the <em>User</em> class to topics directly without worrying about how to serialize POJOs into bytes.</p><div class="language-java codeBlockContainer_Ckt0 theme-code-block" style="--prism-color:#F8F8F2;--prism-background-color:#282A36"><div class="codeBlockContent_biex"><pre tabindex="0" class="prism-code language-java codeBlock_bY9V thin-scrollbar"><code class="codeBlockLines_e6Vv"><span class="token-line" style="color:#F8F8F2"><span class="token comment" style="color:rgb(98, 114, 164)">// send with json schema</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token class-name">Producer</span><span class="token generics punctuation" style="color:rgb(248, 248, 242)"><</span><span class="token generics class-name">User</span><span class="token generics punctuation" style="color:rgb(248, 248, 242)">></span><span class="token plain"> producer </span><span class="token operator">=</span><span class="token plain"> client</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">newProducer</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token class-name">JSONSchema</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">of</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token class-name">User</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">class</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">create</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token class-name">User</span><span class="token plain"> user </span><span class="token operator">=</span><span class="token plain"> </span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">new</span><span class="token plain"> </span><span class="token class-name">User</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token string" style="color:rgb(255, 121, 198)">"Tom"</span><span class="token punctuation" style="color:rgb(248, 248, 242)">,</span><span class="token plain"> </span><span class="token number">28</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain">producer</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">send</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">user</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain" style="display:inline-block"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token comment" style="color:rgb(98, 114, 164)">// receive with json schema</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token class-name">Consumer</span><span class="token generics punctuation" style="color:rgb(248, 248, 242)"><</span><span class="token generics class-name">User</span><span class="token generics punctuation" style="color:rgb(248, 248, 242)">></span><span class="token plain"> consumer </span><span class="token operator">=</span><span class="token plain"> client</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">newConsumer</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token class-name">JSONSchema</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">of</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token class-name">User</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">class</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">topic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token plain">schemaTopic</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">subscriptionInitialPosition</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token class-name">SubscriptionInitialPosition</span><span class="token class-name punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token class-name">Earliest</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">subscriptionName</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token string" style="color:rgb(255, 121, 198)">"schema-sub"</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"> </span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">subscribe</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token class-name">Message</span><span class="token generics punctuation" style="color:rgb(248, 248, 242)"><</span><span class="token generics class-name">User</span><span class="token generics punctuation" style="color:rgb(248, 248, 242)">></span><span class="token plain"> message </span><span class="token operator">=</span><span class="token plain"> consumer</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">receive</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token class-name">User</span><span class="token plain"> user </span><span class="token operator">=</span><span class="token plain"> message</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">getValue</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><span class="token plain"></span><br></span><span class="token-line" style="color:#F8F8F2"><span class="token plain"></span><span class="token keyword" style="color:rgb(189, 147, 249);font-style:italic">assert</span><span class="token plain"> user</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">age </span><span class="token operator">==</span><span class="token plain"> </span><span class="token number">28</span><span class="token plain"> </span><span class="token operator">&&</span><span class="token plain"> user</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token plain">name</span><span class="token punctuation" style="color:rgb(248, 248, 242)">.</span><span class="token function" style="color:rgb(80, 250, 123)">equals</span><span class="token punctuation" style="color:rgb(248, 248, 242)">(</span><span class="token string" style="color:rgb(255, 121, 198)">"Tom"</span><span class="token punctuation" style="color:rgb(248, 248, 242)">)</span><span class="token punctuation" style="color:rgb(248, 248, 242)">;</span><br></span></code></pre><div class="buttonGroup__atx"><button type="button" aria-label="Copy code to clipboard" title="Copy" class="clean-btn"><span class="copyButtonIcons_eSgA" aria-hidden="true"><svg class="copyButtonIcon_y97N" viewBox="0 0 24 24"><path d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"></path></svg><svg class="copyButtonSuccessIcon_LjdS" viewBox="0 0 24 24"><path d="M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z"></path></svg></span></button></div></div></div><h2 class="anchor anchorWithStickyNavbar_LWe7" id="whats-next">What's next?<a href="#whats-next" class="hash-link" aria-label="Direct link to What's next?" title="Direct link to What's next?"></a></h2><ul><li><a href="/docs/3.0.x/schema-understand/">Understand schema concepts</a></li><li><a href="/docs/3.0.x/schema-get-started/">Get started with schema</a></li><li><a href="/docs/3.0.x/admin-api-schemas/">Manage schema</a></li></ul></div><footer class="theme-doc-footer docusaurus-mt-lg"><div class="theme-doc-footer-edit-meta-row row"><div class="col"><a href="https://github.com/apache/pulsar-site/edit/main/versioned_docs/version-3.0.x/schema-overview.md" target="_blank" rel="noreferrer noopener" class="theme-edit-this-page"><svg fill="currentColor" height="20" width="20" viewBox="0 0 40 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