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vp-content><!----><div id="markdown-content"><h1 id="mqtt-protocol" tabindex="-1"><a class="header-anchor" href="#mqtt-protocol"><span>MQTT Protocol</span></a></h1><h2 id="_1-overview" tabindex="-1"><a class="header-anchor" href="#_1-overview"><span>1. Overview</span></a></h2><p>MQTT (Message Queuing Telemetry Transport) is a lightweight messaging protocol designed for IoT and low-bandwidth environments. It operates on a Publish/Subscribe (Pub/Sub) model, enabling efficient and reliable bidirectional communication between devices. Its core objectives are low power consumption, minimal bandwidth usage, and high real-time performance, making it ideal for unstable networks or resource-constrained scenarios (e.g., sensors, mobile devices).</p><p>IoTDB provides deep integration with the MQTT protocol, fully compliant with MQTT v3.1 (OASIS International Standard). The IoTDB server includes a built-in high-performance MQTT Broker module, eliminating the need for third-party middleware. Devices can directly write time-series data into the IoTDB storage engine via MQTT messages.</p><figure><img src="/img/mqtt-table-en-1.png" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><h2 id="_2-configuration" tabindex="-1"><a class="header-anchor" href="#_2-configuration"><span>2. Configuration</span></a></h2><p>By default, the IoTDB MQTT service loads configurations from <code>${IOTDB_HOME}/${IOTDB_CONF}/iotdb-system.properties</code>.</p><table><thead><tr><th><strong>Property</strong></th><th><strong>Description</strong></th><th><strong>Default</strong></th></tr></thead><tbody><tr><td><code>enable_mqtt_service</code></td><td>Enable/ disable the MQTT service.</td><td>FALSE</td></tr><tr><td><code>mqtt_host</code></td><td>Host address bound to the MQTT service.</td><td>127.0.0.1</td></tr><tr><td><code>mqtt_port</code></td><td>Port bound to the MQTT service.</td><td>1883</td></tr><tr><td><code>mqtt_handler_pool_size</code></td><td>Thread pool size for processing MQTT messages.</td><td>1</td></tr><tr><td><strong><code>mqtt_payload_formatter</code></strong></td><td><strong>Formatting method for MQTT message payloads. </strong><strong>Options: <code>json</code> (tree mode), <code>line</code> (table mode).</strong></td><td><strong>json</strong></td></tr><tr><td><code>mqtt_max_message_size</code></td><td>Maximum allowed MQTT message size (bytes).</td><td>1048576</td></tr></tbody></table><h2 id="_3-write-protocol" tabindex="-1"><a class="header-anchor" href="#_3-write-protocol"><span>3. Write Protocol</span></a></h2><ul><li>Line Protocol Syntax</li></ul><div class="language-javascript line-numbers-mode" data-highlighter="shiki" data-ext="javascript" style="background-color:#282c34;color:#abb2bf;"><pre class="shiki one-dark-pro vp-code"><code class="language-javascript"><span class="line"><span style="color:#ABB2BF;"><</span><span style="color:#E06C75;">measurement</span><span style="color:#ABB2BF;">>[,<</span><span style="color:#E5C07B;">tag_key</span><span style="color:#ABB2BF;">>=<</span><span style="color:#E5C07B;">tag_value</span><span style="color:#ABB2BF;">>[,<</span><span style="color:#E5C07B;">tag_key</span><span style="color:#ABB2BF;">>=<</span><span style="color:#E5C07B;">tag_value</span><span style="color:#ABB2BF;">>]][ <</span><span style="color:#E5C07B;">attribute_key</span><span style="color:#ABB2BF;">>=<</span><span style="color:#E5C07B;">attribute_value</span><span style="color:#ABB2BF;">>[,<</span><span style="color:#E5C07B;">attribute_key</span><span style="color:#ABB2BF;">>=<</span><span style="color:#E5C07B;">attribute_value</span><span style="color:#ABB2BF;">>]] <</span><span style="color:#E5C07B;">field_key</span><span style="color:#ABB2BF;">>=<</span><span style="color:#E5C07B;">field_value</span><span style="color:#ABB2BF;">>[,<</span><span style="color:#E5C07B;">field_key</span><span style="color:#ABB2BF;">>=<</span><span style="color:#E5C07B;">field_value</span><span style="color:#ABB2BF;">>] [<</span><span style="color:#E06C75;">timestamp</span><span style="color:#ABB2BF;">>]</span></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div></div></div><ul><li>Example</li></ul><div class="language-javascript line-numbers-mode" data-highlighter="shiki" data-ext="javascript" style="background-color:#282c34;color:#abb2bf;"><pre class="shiki one-dark-pro vp-code"><code class="language-javascript"><span class="line"><span style="color:#E06C75;">myMeasurement</span><span style="color:#ABB2BF;">,</span><span style="color:#E06C75;">tag1</span><span style="color:#56B6C2;">=</span><span style="color:#E06C75;">value1</span><span style="color:#ABB2BF;">,</span><span style="color:#E06C75;">tag2</span><span style="color:#56B6C2;">=</span><span style="color:#E06C75;">value2</span><span style="color:#E06C75;"> attr1</span><span style="color:#56B6C2;">=</span><span style="color:#E06C75;">value1</span><span style="color:#ABB2BF;">,</span><span style="color:#E06C75;">attr2</span><span style="color:#56B6C2;">=</span><span style="color:#E06C75;">value2</span><span style="color:#E06C75;"> fieldKey</span><span style="color:#56B6C2;">=</span><span style="color:#98C379;">"fieldValue"</span><span style="color:#D19A66;"> 1556813561098000000</span></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div></div></div><figure><img src="/img/mqtt-table-en-2.png" alt="" tabindex="0" loading="lazy"><figcaption></figcaption></figure><h2 id="_4-naming-conventions" tabindex="-1"><a class="header-anchor" href="#_4-naming-conventions"><span>4. Naming Conventions</span></a></h2><ul><li>Database Name</li></ul><p>The first segment of the MQTT topic (split by <code>/</code>) is used as the database name.</p><div class="language-properties line-numbers-mode" data-highlighter="shiki" data-ext="properties" style="background-color:#282c34;color:#abb2bf;"><pre class="shiki one-dark-pro vp-code"><code class="language-properties"><span class="line"><span style="color:#98C379;">topic: stock/Legacy</span></span> |
| <span class="line"><span style="color:#98C379;">databaseName: stock</span></span> |
| <span class="line"></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#98C379;">topic: stock/Legacy/</span><span style="color:#7F848E;font-style:italic;">#</span></span> |
| <span class="line"><span style="color:#98C379;">databaseName:stock</span></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><ul><li>Table Name</li></ul><p>The table name is derived from the <code><measurement></code> in the line protocol.</p><ul><li>Type Identifiers</li></ul><table><thead><tr><th>Filed Value</th><th>IoTDB Data Type</th></tr></thead><tbody><tr><td>1<br>1.12</td><td>DOUBLE</td></tr><tr><td>1<code>f</code><br>1.12<code>f</code></td><td>FLOAT</td></tr><tr><td>1<code>i</code><br>123<code>i</code></td><td>INT64</td></tr><tr><td>1<code>u</code><br>123<code>u</code></td><td>INT64</td></tr><tr><td>1<code>i32</code><br>123<code>i32</code></td><td>INT32</td></tr><tr><td><code>"xxx"</code></td><td>TEXT</td></tr><tr><td><code>t</code>,<code>T</code>,<code>true</code>,<code>True</code>,<code>TRUE</code><br> <code>f</code>,<code>F</code>,<code>false</code>,<code>False</code>,<code>FALSE</code></td><td>BOOLEAN</td></tr></tbody></table><h2 id="_5-coding-examples" tabindex="-1"><a class="header-anchor" href="#_5-coding-examples"><span>5. Coding Examples</span></a></h2><p>The following is an example which a mqtt client send messages to IoTDB server.</p><div class="language-java line-numbers-mode" data-highlighter="shiki" data-ext="java" style="background-color:#282c34;color:#abb2bf;"><pre class="shiki one-dark-pro vp-code"><code class="language-java"><span class="line"><span style="color:#E5C07B;">MQTT</span><span style="color:#E06C75;"> mqtt </span><span style="color:#56B6C2;">=</span><span style="color:#C678DD;"> new</span><span style="color:#61AFEF;"> MQTT</span><span style="color:#E06C75;">()</span><span style="color:#ABB2BF;">;</span></span> |
| <span class="line"><span style="color:#E5C07B;">mqtt</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">setHost</span><span style="color:#ABB2BF;">(</span><span style="color:#98C379;">"127.0.0.1"</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">1883</span><span style="color:#ABB2BF;">);</span></span> |
| <span class="line"><span style="color:#E5C07B;">mqtt</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">setUserName</span><span style="color:#ABB2BF;">(</span><span style="color:#98C379;">"root"</span><span style="color:#ABB2BF;">);</span></span> |
| <span class="line"><span style="color:#E5C07B;">mqtt</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">setPassword</span><span style="color:#ABB2BF;">(</span><span style="color:#98C379;">"root"</span><span style="color:#ABB2BF;">);</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#E5C07B;">BlockingConnection</span><span style="color:#E06C75;"> connection </span><span style="color:#56B6C2;">=</span><span style="color:#E5C07B;"> mqtt</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">blockingConnection</span><span style="color:#ABB2BF;">();</span></span> |
| <span class="line"><span style="color:#E5C07B;">String</span><span style="color:#E06C75;"> DATABASE </span><span style="color:#56B6C2;">=</span><span style="color:#98C379;"> "myMqttTest"</span><span style="color:#ABB2BF;">;</span></span> |
| <span class="line"><span style="color:#E5C07B;">connection</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">connect</span><span style="color:#ABB2BF;">();</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#E5C07B;">String</span><span style="color:#E06C75;"> payload </span><span style="color:#56B6C2;">=</span></span> |
| <span class="line"><span style="color:#98C379;"> "test1,tag1=t1,tag2=t2 attr3=a5,attr4=a4 field1=</span><span style="color:#56B6C2;">\"</span><span style="color:#98C379;">fieldValue1</span><span style="color:#56B6C2;">\"</span><span style="color:#98C379;">,field2=1i,field3=1u 1"</span><span style="color:#ABB2BF;">;</span></span> |
| <span class="line"><span style="color:#E5C07B;">connection</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">publish</span><span style="color:#ABB2BF;">(DATABASE </span><span style="color:#56B6C2;">+</span><span style="color:#98C379;"> "/myTopic"</span><span style="color:#ABB2BF;">, </span><span style="color:#E5C07B;">payload</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">getBytes</span><span style="color:#ABB2BF;">(), </span><span style="color:#E5C07B;">QoS</span><span style="color:#ABB2BF;">.</span><span style="color:#E5C07B;">AT_LEAST_ONCE</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">false</span><span style="color:#ABB2BF;">);</span></span> |
| <span class="line"><span style="color:#E5C07B;">Thread</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">sleep</span><span style="color:#ABB2BF;">(</span><span style="color:#D19A66;">10</span><span style="color:#ABB2BF;">);</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#E06C75;">payload </span><span style="color:#56B6C2;">=</span><span style="color:#98C379;"> "test1,tag1=t1,tag2=t2 field4=2,field5=2i32,field6=2f 2"</span><span style="color:#ABB2BF;">;</span></span> |
| <span class="line"><span style="color:#E5C07B;">connection</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">publish</span><span style="color:#ABB2BF;">(DATABASE, </span><span style="color:#E5C07B;">payload</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">getBytes</span><span style="color:#ABB2BF;">(), </span><span style="color:#E5C07B;">QoS</span><span style="color:#ABB2BF;">.</span><span style="color:#E5C07B;">AT_LEAST_ONCE</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">false</span><span style="color:#ABB2BF;">);</span></span> |
| <span class="line"><span style="color:#E5C07B;">Thread</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">sleep</span><span style="color:#ABB2BF;">(</span><span style="color:#D19A66;">10</span><span style="color:#ABB2BF;">);</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#E06C75;">payload </span><span style="color:#56B6C2;">=</span><span style="color:#98C379;"> "# It's a remark</span><span style="color:#56B6C2;">\n</span><span style="color:#98C379;"> "</span><span style="color:#56B6C2;"> +</span><span style="color:#98C379;"> "test1,tag1=t1,tag2=t2 field4=2,field5=2i32,field6=2f 6"</span><span style="color:#ABB2BF;">;</span></span> |
| <span class="line"><span style="color:#E5C07B;"> connection</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">publish</span><span style="color:#ABB2BF;">(DATABASE </span><span style="color:#56B6C2;">+</span><span style="color:#98C379;"> "/myTopic"</span><span style="color:#ABB2BF;">, </span><span style="color:#E5C07B;">payload</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">getBytes</span><span style="color:#ABB2BF;">(), </span><span style="color:#E5C07B;">QoS</span><span style="color:#ABB2BF;">.</span><span style="color:#E5C07B;">AT_LEAST_ONCE</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">false</span><span style="color:#ABB2BF;">);</span></span> |
| <span class="line"><span style="color:#E5C07B;"> Thread</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">sleep</span><span style="color:#ABB2BF;">(</span><span style="color:#D19A66;">10</span><span style="color:#ABB2BF;">);</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#7F848E;font-style:italic;">//batch write example </span></span> |
| <span class="line"><span style="color:#E06C75;">payload </span><span style="color:#56B6C2;">=</span></span> |
| <span class="line"><span style="color:#98C379;"> "test1,tag1=t1,tag2=t2 field7=t,field8=T,field9=true 3 </span><span style="color:#56B6C2;">\n</span><span style="color:#98C379;"> "</span></span> |
| <span class="line"><span style="color:#56B6C2;"> +</span><span style="color:#98C379;"> "test1,tag1=t1,tag2=t2 field7=f,field8=F,field9=FALSE 4"</span><span style="color:#ABB2BF;">;</span></span> |
| <span class="line"><span style="color:#E5C07B;">connection</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">publish</span><span style="color:#ABB2BF;">(DATABASE </span><span style="color:#56B6C2;">+</span><span style="color:#98C379;"> "/myTopic"</span><span style="color:#ABB2BF;">, </span><span style="color:#E5C07B;">payload</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">getBytes</span><span style="color:#ABB2BF;">(), </span><span style="color:#E5C07B;">QoS</span><span style="color:#ABB2BF;">.</span><span style="color:#E5C07B;">AT_LEAST_ONCE</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">false</span><span style="color:#ABB2BF;">);</span></span> |
| <span class="line"><span style="color:#E5C07B;">Thread</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">sleep</span><span style="color:#ABB2BF;">(</span><span style="color:#D19A66;">10</span><span style="color:#ABB2BF;">);</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#7F848E;font-style:italic;">//batch write example</span></span> |
| <span class="line"><span style="color:#E06C75;">payload </span><span style="color:#56B6C2;">=</span></span> |
| <span class="line"><span style="color:#98C379;"> "test1,tag1=t1,tag2=t2 attr1=a1,attr2=a2 field1=</span><span style="color:#56B6C2;">\"</span><span style="color:#98C379;">fieldValue1</span><span style="color:#56B6C2;">\"</span><span style="color:#98C379;">,field2=1i,field3=1u 4 </span><span style="color:#56B6C2;">\n</span><span style="color:#98C379;"> "</span></span> |
| <span class="line"><span style="color:#56B6C2;"> +</span><span style="color:#98C379;"> "test1,tag1=t1,tag2=t2 field4=2,field5=2i32,field6=2f 5"</span><span style="color:#ABB2BF;">;</span></span> |
| <span class="line"><span style="color:#E5C07B;">connection</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">publish</span><span style="color:#ABB2BF;">(DATABASE </span><span style="color:#56B6C2;">+</span><span style="color:#98C379;"> "/myTopic"</span><span style="color:#ABB2BF;">, </span><span style="color:#E5C07B;">payload</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">getBytes</span><span style="color:#ABB2BF;">(), </span><span style="color:#E5C07B;">QoS</span><span style="color:#ABB2BF;">.</span><span style="color:#E5C07B;">AT_LEAST_ONCE</span><span style="color:#ABB2BF;">, </span><span style="color:#D19A66;">false</span><span style="color:#ABB2BF;">);</span></span> |
| <span class="line"><span style="color:#E5C07B;">Thread</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">sleep</span><span style="color:#ABB2BF;">(</span><span style="color:#D19A66;">10</span><span style="color:#ABB2BF;">);</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#E5C07B;">connection</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">disconnect</span><span style="color:#ABB2BF;">();</span></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><h2 id="_6-customize-your-mqtt-message-format" tabindex="-1"><a class="header-anchor" href="#_6-customize-your-mqtt-message-format"><span>6. Customize your MQTT Message Format</span></a></h2><p>If you do not like the above Line format, you can customize your MQTT Message format by just writing several lines<br> of codes. An example can be found in <a href="https://github.com/apache/iotdb/tree/master/example/mqtt-customize" target="_blank" rel="noopener noreferrer">example/mqtt-customize</a> project.</p><p>Steps:</p><ol><li>Create a java project, and add dependency:</li></ol><div class="language-xml line-numbers-mode" data-highlighter="shiki" data-ext="xml" style="background-color:#282c34;color:#abb2bf;"><pre class="shiki one-dark-pro vp-code"><code class="language-xml"><span class="line"><span style="color:#ABB2BF;"> <</span><span style="color:#E06C75;">dependency</span><span style="color:#ABB2BF;">></span></span> |
| <span class="line"><span style="color:#ABB2BF;"> <</span><span style="color:#E06C75;">groupId</span><span style="color:#ABB2BF;">>org.apache.iotdb</</span><span style="color:#E06C75;">groupId</span><span style="color:#ABB2BF;">></span></span> |
| <span class="line"><span style="color:#ABB2BF;"> <</span><span style="color:#E06C75;">artifactId</span><span style="color:#ABB2BF;">>iotdb-server</</span><span style="color:#E06C75;">artifactId</span><span style="color:#ABB2BF;">></span></span> |
| <span class="line"><span style="color:#ABB2BF;"> <</span><span style="color:#E06C75;">version</span><span style="color:#ABB2BF;">>2.0.4-SNAPSHOT</</span><span style="color:#E06C75;">version</span><span style="color:#ABB2BF;">></span></span> |
| <span class="line"><span style="color:#ABB2BF;"> </</span><span style="color:#E06C75;">dependency</span><span style="color:#ABB2BF;">></span></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><ol start="2"><li>Define your implementation which implements <code>org.apache.iotdb.db.protocol.mqtt.PayloadFormatter</code><br> e.g.,</li></ol><div class="language-java line-numbers-mode" data-highlighter="shiki" data-ext="java" style="background-color:#282c34;color:#abb2bf;"><pre class="shiki one-dark-pro vp-code"><code class="language-java"><span class="line"><span style="color:#C678DD;">package</span><span style="color:#C678DD;"> org.apache.iotdb.mqtt.server</span><span style="color:#ABB2BF;">;</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#C678DD;">import</span><span style="color:#E5C07B;"> io.netty.buffer.ByteBuf</span><span style="color:#ABB2BF;">;</span></span> |
| <span class="line"><span style="color:#C678DD;">import</span><span style="color:#E5C07B;"> org.apache.iotdb.db.protocol.mqtt.Message</span><span style="color:#ABB2BF;">;</span></span> |
| <span class="line"><span style="color:#C678DD;">import</span><span style="color:#E5C07B;"> org.apache.iotdb.db.protocol.mqtt.PayloadFormatter</span><span style="color:#ABB2BF;">;</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#C678DD;">import</span><span style="color:#E5C07B;"> java.nio.charset.StandardCharsets</span><span style="color:#ABB2BF;">;</span></span> |
| <span class="line"><span style="color:#C678DD;">import</span><span style="color:#E5C07B;"> java.util.ArrayList</span><span style="color:#ABB2BF;">;</span></span> |
| <span class="line"><span style="color:#C678DD;">import</span><span style="color:#E5C07B;"> java.util.Arrays</span><span style="color:#ABB2BF;">;</span></span> |
| <span class="line"><span style="color:#C678DD;">import</span><span style="color:#E5C07B;"> java.util.List</span><span style="color:#ABB2BF;">;</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#C678DD;">public</span><span style="color:#C678DD;"> class</span><span style="color:#E5C07B;"> CustomizedLinePayloadFormatter</span><span style="color:#C678DD;"> implements</span><span style="color:#E5C07B;"> PayloadFormatter</span><span style="color:#ABB2BF;"> {</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#ABB2BF;"> @</span><span style="color:#E5C07B;">Override</span></span> |
| <span class="line"><span style="color:#C678DD;"> public</span><span style="color:#E5C07B;"> List</span><span style="color:#ABB2BF;"><</span><span style="color:#E5C07B;">Message</span><span style="color:#ABB2BF;">></span><span style="color:#61AFEF;"> format</span><span style="color:#ABB2BF;">(</span><span style="color:#E5C07B;">String</span><span style="color:#E06C75;font-style:italic;"> topic</span><span style="color:#ABB2BF;">, </span><span style="color:#E5C07B;">ByteBuf</span><span style="color:#E06C75;font-style:italic;"> payload</span><span style="color:#ABB2BF;">)</span><span style="color:#ABB2BF;"> {</span></span> |
| <span class="line"><span style="color:#7F848E;font-style:italic;"> // Suppose the payload is a line format</span></span> |
| <span class="line"><span style="color:#C678DD;"> if</span><span style="color:#ABB2BF;"> (payload </span><span style="color:#56B6C2;">==</span><span style="color:#D19A66;"> null</span><span style="color:#ABB2BF;">) {</span></span> |
| <span class="line"><span style="color:#C678DD;"> return</span><span style="color:#D19A66;"> null</span><span style="color:#ABB2BF;">;</span></span> |
| <span class="line"><span style="color:#ABB2BF;"> }</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#E5C07B;"> String</span><span style="color:#E06C75;"> line</span><span style="color:#56B6C2;"> =</span><span style="color:#E5C07B;"> payload</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">toString</span><span style="color:#ABB2BF;">(</span><span style="color:#E5C07B;">StandardCharsets</span><span style="color:#ABB2BF;">.</span><span style="color:#E5C07B;">UTF_8</span><span style="color:#ABB2BF;">);</span></span> |
| <span class="line"><span style="color:#7F848E;font-style:italic;"> // parse data from the line and generate Messages and put them into List<Meesage> ret</span></span> |
| <span class="line"><span style="color:#E5C07B;"> List</span><span style="color:#ABB2BF;"><</span><span style="color:#E5C07B;">Message</span><span style="color:#ABB2BF;">> </span><span style="color:#E06C75;">ret</span><span style="color:#56B6C2;"> =</span><span style="color:#C678DD;"> new</span><span style="color:#E5C07B;"> ArrayList</span><span style="color:#ABB2BF;"><>();</span></span> |
| <span class="line"><span style="color:#7F848E;font-style:italic;"> // this is just an example, so we just generate some Messages directly</span></span> |
| <span class="line"><span style="color:#C678DD;"> for</span><span style="color:#ABB2BF;"> (</span><span style="color:#C678DD;">int</span><span style="color:#E06C75;"> i</span><span style="color:#56B6C2;"> =</span><span style="color:#D19A66;"> 0</span><span style="color:#ABB2BF;">; i </span><span style="color:#56B6C2;"><</span><span style="color:#D19A66;"> 3</span><span style="color:#ABB2BF;">; i++) {</span></span> |
| <span class="line"><span style="color:#C678DD;"> long</span><span style="color:#E06C75;"> ts</span><span style="color:#56B6C2;"> =</span><span style="color:#ABB2BF;"> i;</span></span> |
| <span class="line"><span style="color:#E5C07B;"> TableMessage</span><span style="color:#E06C75;"> message</span><span style="color:#56B6C2;"> =</span><span style="color:#C678DD;"> new</span><span style="color:#61AFEF;"> TableMessage</span><span style="color:#ABB2BF;">();</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#7F848E;font-style:italic;"> // Parsing Database Name</span></span> |
| <span class="line"><span style="color:#E5C07B;"> message</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">setDatabase</span><span style="color:#ABB2BF;">(</span><span style="color:#98C379;">"db"</span><span style="color:#56B6C2;"> +</span><span style="color:#ABB2BF;"> i);</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#7F848E;font-style:italic;"> //Parsing Table Names</span></span> |
| <span class="line"><span style="color:#E5C07B;"> message</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">setTable</span><span style="color:#ABB2BF;">(</span><span style="color:#98C379;">"t"</span><span style="color:#56B6C2;"> +</span><span style="color:#ABB2BF;"> i);</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#7F848E;font-style:italic;"> // Parsing Tags</span></span> |
| <span class="line"><span style="color:#E5C07B;"> List</span><span style="color:#ABB2BF;"><</span><span style="color:#E5C07B;">String</span><span style="color:#ABB2BF;">> </span><span style="color:#E06C75;">tagKeys</span><span style="color:#56B6C2;"> =</span><span style="color:#C678DD;"> new</span><span style="color:#E5C07B;"> ArrayList</span><span style="color:#ABB2BF;"><>();</span></span> |
| <span class="line"><span style="color:#E5C07B;"> tagKeys</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">add</span><span style="color:#ABB2BF;">(</span><span style="color:#98C379;">"tag1"</span><span style="color:#56B6C2;"> +</span><span style="color:#ABB2BF;"> i);</span></span> |
| <span class="line"><span style="color:#E5C07B;"> tagKeys</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">add</span><span style="color:#ABB2BF;">(</span><span style="color:#98C379;">"tag2"</span><span style="color:#56B6C2;"> +</span><span style="color:#ABB2BF;"> i);</span></span> |
| <span class="line"><span style="color:#E5C07B;"> List</span><span style="color:#ABB2BF;"><</span><span style="color:#E5C07B;">Object</span><span style="color:#ABB2BF;">> </span><span style="color:#E06C75;">tagValues</span><span style="color:#56B6C2;"> =</span><span style="color:#C678DD;"> new</span><span style="color:#E5C07B;"> ArrayList</span><span style="color:#ABB2BF;"><>();</span></span> |
| <span class="line"><span style="color:#E5C07B;"> tagValues</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">add</span><span style="color:#ABB2BF;">(</span><span style="color:#98C379;">"t_value1"</span><span style="color:#56B6C2;"> +</span><span style="color:#ABB2BF;"> i);</span></span> |
| <span class="line"><span style="color:#E5C07B;"> tagValues</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">add</span><span style="color:#ABB2BF;">(</span><span style="color:#98C379;">"t_value2"</span><span style="color:#56B6C2;"> +</span><span style="color:#ABB2BF;"> i);</span></span> |
| <span class="line"><span style="color:#E5C07B;"> message</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">setTagKeys</span><span style="color:#ABB2BF;">(tagKeys);</span></span> |
| <span class="line"><span style="color:#E5C07B;"> message</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">setTagValues</span><span style="color:#ABB2BF;">(tagValues);</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#7F848E;font-style:italic;"> // Parsing Attributes</span></span> |
| <span class="line"><span style="color:#E5C07B;"> List</span><span style="color:#ABB2BF;"><</span><span style="color:#E5C07B;">String</span><span style="color:#ABB2BF;">> </span><span style="color:#E06C75;">attributeKeys</span><span style="color:#56B6C2;"> =</span><span style="color:#C678DD;"> new</span><span style="color:#E5C07B;"> ArrayList</span><span style="color:#ABB2BF;"><>();</span></span> |
| <span class="line"><span style="color:#E5C07B;"> List</span><span style="color:#ABB2BF;"><</span><span style="color:#E5C07B;">Object</span><span style="color:#ABB2BF;">> </span><span style="color:#E06C75;">attributeValues</span><span style="color:#56B6C2;"> =</span><span style="color:#C678DD;"> new</span><span style="color:#E5C07B;"> ArrayList</span><span style="color:#ABB2BF;"><>();</span></span> |
| <span class="line"><span style="color:#E5C07B;"> attributeKeys</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">add</span><span style="color:#ABB2BF;">(</span><span style="color:#98C379;">"attr1"</span><span style="color:#56B6C2;"> +</span><span style="color:#ABB2BF;"> i);</span></span> |
| <span class="line"><span style="color:#E5C07B;"> attributeKeys</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">add</span><span style="color:#ABB2BF;">(</span><span style="color:#98C379;">"attr2"</span><span style="color:#56B6C2;"> +</span><span style="color:#ABB2BF;"> i);</span></span> |
| <span class="line"><span style="color:#E5C07B;"> attributeValues</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">add</span><span style="color:#ABB2BF;">(</span><span style="color:#98C379;">"a_value1"</span><span style="color:#56B6C2;"> +</span><span style="color:#ABB2BF;"> i);</span></span> |
| <span class="line"><span style="color:#E5C07B;"> attributeValues</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">add</span><span style="color:#ABB2BF;">(</span><span style="color:#98C379;">"a_value2"</span><span style="color:#56B6C2;"> +</span><span style="color:#ABB2BF;"> i);</span></span> |
| <span class="line"><span style="color:#E5C07B;"> message</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">setAttributeKeys</span><span style="color:#ABB2BF;">(attributeKeys);</span></span> |
| <span class="line"><span style="color:#E5C07B;"> message</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">setAttributeValues</span><span style="color:#ABB2BF;">(attributeValues);</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#7F848E;font-style:italic;"> // Parsing Fields</span></span> |
| <span class="line"><span style="color:#E5C07B;"> List</span><span style="color:#ABB2BF;"><</span><span style="color:#E5C07B;">String</span><span style="color:#ABB2BF;">> </span><span style="color:#E06C75;">fields</span><span style="color:#56B6C2;"> =</span><span style="color:#E5C07B;"> Arrays</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">asList</span><span style="color:#ABB2BF;">(</span><span style="color:#98C379;">"field1"</span><span style="color:#56B6C2;"> +</span><span style="color:#ABB2BF;"> i, </span><span style="color:#98C379;">"field2"</span><span style="color:#56B6C2;"> +</span><span style="color:#ABB2BF;"> i);</span></span> |
| <span class="line"><span style="color:#E5C07B;"> List</span><span style="color:#ABB2BF;"><</span><span style="color:#E5C07B;">TSDataType</span><span style="color:#ABB2BF;">> </span><span style="color:#E06C75;">dataTypes</span><span style="color:#56B6C2;"> =</span><span style="color:#E5C07B;"> Arrays</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">asList</span><span style="color:#ABB2BF;">(</span><span style="color:#E5C07B;">TSDataType</span><span style="color:#ABB2BF;">.</span><span style="color:#E5C07B;">FLOAT</span><span style="color:#ABB2BF;">, </span><span style="color:#E5C07B;">TSDataType</span><span style="color:#ABB2BF;">.</span><span style="color:#E5C07B;">FLOAT</span><span style="color:#ABB2BF;">);</span></span> |
| <span class="line"><span style="color:#E5C07B;"> List</span><span style="color:#ABB2BF;"><</span><span style="color:#E5C07B;">Object</span><span style="color:#ABB2BF;">> </span><span style="color:#E06C75;">values</span><span style="color:#56B6C2;"> =</span><span style="color:#E5C07B;"> Arrays</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">asList</span><span style="color:#ABB2BF;">(</span><span style="color:#98C379;">"4.0"</span><span style="color:#56B6C2;"> +</span><span style="color:#ABB2BF;"> i, </span><span style="color:#98C379;">"5.0"</span><span style="color:#56B6C2;"> +</span><span style="color:#ABB2BF;"> i);</span></span> |
| <span class="line"><span style="color:#E5C07B;"> message</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">setFields</span><span style="color:#ABB2BF;">(fields);</span></span> |
| <span class="line"><span style="color:#E5C07B;"> message</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">setDataTypes</span><span style="color:#ABB2BF;">(dataTypes);</span></span> |
| <span class="line"><span style="color:#E5C07B;"> message</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">setValues</span><span style="color:#ABB2BF;">(values);</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#7F848E;font-style:italic;"> //// Parsing timestamp</span></span> |
| <span class="line"><span style="color:#E5C07B;"> message</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">setTimestamp</span><span style="color:#ABB2BF;">(ts);</span></span> |
| <span class="line"><span style="color:#E5C07B;"> ret</span><span style="color:#ABB2BF;">.</span><span style="color:#61AFEF;">add</span><span style="color:#ABB2BF;">(message);</span></span> |
| <span class="line"><span style="color:#ABB2BF;"> }</span></span> |
| <span class="line"><span style="color:#C678DD;"> return</span><span style="color:#ABB2BF;"> ret;</span></span> |
| <span class="line"><span style="color:#ABB2BF;"> }</span></span> |
| <span class="line"></span> |
| <span class="line"><span style="color:#ABB2BF;"> @</span><span style="color:#E5C07B;">Override</span></span> |
| <span class="line"><span style="color:#C678DD;"> public</span><span style="color:#E5C07B;"> String</span><span style="color:#61AFEF;"> getName</span><span style="color:#ABB2BF;">()</span><span style="color:#ABB2BF;"> {</span></span> |
| <span class="line"><span style="color:#7F848E;font-style:italic;"> // set the value of mqtt_payload_formatter in iotdb-system.properties as the following string:</span></span> |
| <span class="line"><span style="color:#C678DD;"> return</span><span style="color:#98C379;"> "CustomizedLine"</span><span style="color:#ABB2BF;">;</span></span> |
| <span class="line"><span style="color:#ABB2BF;"> }</span></span> |
| <span class="line"><span style="color:#ABB2BF;">}</span></span></code></pre><div class="line-numbers" aria-hidden="true" style="counter-reset:line-number 0;"><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div><div class="line-number"></div></div></div><ol start="3"><li>modify the file in <code>src/main/resources/META-INF/services/org.apache.iotdb.db.protocol.mqtt.PayloadFormatter</code>:<br> clean the file and put your implementation class name into the file.<br> In this example, the content is: <code>org.apache.iotdb.mqtt.server.CustomizedLinePayloadFormatter</code></li><li>compile your implementation as a jar file: <code>mvn package -DskipTests</code></li></ol><p>Then, in your server:</p><ol><li>Create ${IOTDB_HOME}/ext/mqtt/ folder, and put the jar into this folder.</li><li>Update configuration to enable MQTT service. (<code>enable_mqtt_service=true</code> in <code>conf/iotdb-system.properties</code>)</li><li>Set the value of <code>mqtt_payload_formatter</code> in <code>conf/iotdb-system.properties</code> as the value of getName() in your implementation<br> , in this example, the value is <code>CustomizedLine</code></li><li>Launch the IoTDB server.</li><li>Now IoTDB will use your implementation to parse the MQTT message.</li></ol><p>More: the message format can be anything you want. For example, if it is a binary format,<br> just use <code>payload.forEachByte()</code> or <code>payload.array</code> to get bytes content.</p><h2 id="_7-caution" tabindex="-1"><a class="header-anchor" href="#_7-caution"><span>7. Caution</span></a></h2><p>To avoid compatibility issues caused by a default client_id, always explicitly supply a unique, non-empty client_id in every MQTT client.<br> Behavior varies when the client_id is missing or empty. Common examples:</p><ol><li>Explicitly sending an empty string<br> • MQTTX: When client_id="", IoTDB silently discards the message.<br> • mosquitto_pub: When client_id="", IoTDB receives the message normally.</li><li>Omitting client_id entirely<br> • MQTTX: IoTDB accepts the message.<br> • mosquitto_pub: IoTDB rejects the connection.<br> Therefore, explicitly assigning a unique, non-empty client_id is the simplest way to eliminate these discrepancies and ensure reliable message delivery.</li></ol></div><!----><!----><!----></div><footer class="vp-page-meta"><div class="vp-meta-item edit-link"><a class="auto-link external-link vp-meta-label" href="https://github.com/apache/iotdb-docs/edit/main/src/UserGuide/latest-Table/API/Programming-MQTT_apache.md" aria-label="Found Error? 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