[Doc] add explanations for entry filter (#13646)
diff --git a/site2/docs/develop-plugin.md b/site2/docs/develop-plugin.md
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+---
+id: develop-plugin
+title: Pulsar plugin development
+sidebar_label: Plugin
+---
+
+You can develop various plugins for Pulsar, such as entry filters, protocol handlers, interceptors, and so on.
+
+## Entry filter
+
+This chapter describes what the entry filter is and shows how to use the entry filter.
+
+### What is an entry filter?
+
+The entry filter is an extension point for implementing a custom message entry strategy. With an entry filter, you can decide **whether to send messages to consumers** (brokers can use the return values of entry filters to determine whether the messages need to be sent or discarded) or **send messages to specific consumers.**
+
+To implement features such as tagged messages or custom delayed messages, use [`subscriptionProperties`](https://github.com/apache/pulsar/blob/ec0a44058d249a7510bb3d05685b2ee5e0874eb6/pulsar-client-api/src/main/java/org/apache/pulsar/client/api/ConsumerBuilder.java?_pjax=%23js-repo-pjax-container%2C%20div%5Bitemtype%3D%22http%3A%2F%2Fschema.org%2FSoftwareSourceCode%22%5D%20main%2C%20%5Bdata-pjax-container%5D#L174), [`​​properties`](https://github.com/apache/pulsar/blob/ec0a44058d249a7510bb3d05685b2ee5e0874eb6/pulsar-client-api/src/main/java/org/apache/pulsar/client/api/ConsumerBuilder.java?_pjax=%23js-repo-pjax-container%2C%20div%5Bitemtype%3D%22http%3A%2F%2Fschema.org%2FSoftwareSourceCode%22%5D%20main%2C%20%5Bdata-pjax-container%5D#L533), and entry filters.
+
+### How to use an entry filter?
+
+Follow the steps below:
+
+1. Create a Maven project.
+
+2. Implement the `EntryFilter` interface.
+
+3. Package the implementation class into a NAR file.
+
+4. Configure the `broker.conf` file (or the `standalone.conf` file) and restart your broker.
+
+#### Step 1: Create a Maven project
+
+For how to create a Maven project, see [here](https://maven.apache.org/guides/getting-started/maven-in-five-minutes.html).
+
+#### Step 2: Implement the `EntryFilter` interface
+
+1. Add a dependency for Pulsar broker in the `pom.xml` file to display. Otherwise, you can not find the [`EntryFilter` interface](https://github.com/apache/pulsar/blob/master/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/plugin/EntryFilter.java).
+
+ ```xml
+ <dependency>
+ <groupId>org.apache.pulsar</groupId>
+ <artifactId>pulsar-broker</artifactId>
+ <version>${pulsar.version}</version>
+ <scope>provided</scope>
+ </dependency>
+ ```
+
+2. Implement the [`FilterResult filterEntry(Entry entry, FilterContext context);` method](https://github.com/apache/pulsar/blob/2adb6661d5b82c5705ee00ce3ebc9941c99635d5/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/plugin/EntryFilter.java#L34).
+
+ - If the method returns `ACCEPT` or NULL, this message is sent to consumers.
+
+ - If the method returns `REJECT`, this message is filtered out and it does not consume message permits.
+
+ - If there are multiple entry filters, this message passes through all filters in the pipeline in a round-robin manner. If any entry filter returns `REJECT`, this message is discarded.
+
+ You can get entry metadata, subscriptions, and other information through `FilterContext`.
+
+3. Describe a NAR file.
+
+ Create an `entry_filter.yaml` file in the `resources/META-INF/services` directory to describe a NAR file.
+
+ ```conf
+ # Entry filter name, which should be configured in the broker.conf file later
+ name: entryFilter
+ # Entry filter description
+ description: entry filter
+ # Implementation class name of entry filter
+ entryFilterClass: com.xxxx.xxxx.xxxx.DefaultEntryFilterImpl
+ ```
+
+#### Step 3: package implementation class of entry filter into a NAR file
+
+1. Add the compiled plugin of the NAR file to your `pom.xml` file.
+
+ ```xml
+ <build>
+ <finalName>${project.artifactId}</finalName>
+ <plugins>
+ <plugin>
+ <groupId>org.apache.nifi</groupId>
+ <artifactId>nifi-nar-maven-plugin</artifactId>
+ <version>1.2.0</version>
+ <extensions>true</extensions>
+ <configuration>
+ <finalName>${project.artifactId}-${project.version}</finalName>
+ </configuration>
+ <executions>
+ <execution>
+ <id>default-nar</id>
+ <phase>package</phase>
+ <goals>
+ <goal>nar</goal>
+ </goals>
+ </execution>
+ </executions>
+ </plugin>
+ </plugins>
+ </build>
+ ```
+
+2. Generate a NAR file in the `target` directory.
+
+ ```script
+ mvn clean install
+ ```
+
+#### Step 4: configure and restart broker
+
+1. Configure the following parameters in the `broker.conf` file (or the `standalone.conf` file).
+
+ ```conf
+ # Class name of pluggable entry filters
+ # Multiple classes need to be separated by commas.
+ entryFilterNames=entryFilter1,entryFilter2,entryFilter3
+ # The directory for all entry filter implementations
+ entryFiltersDirectory=tempDir
+ ```
+
+2. Restart your broker.
+
+ You can see the following broker log if the plug-in is successfully loaded.
+
+ ```text
+ Successfully loaded entry filter for name `{name of your entry filter}`
+ ```
diff --git a/site2/website/contributing.md b/site2/website/contributing.md
index f63a332..d7b6f61 100644
--- a/site2/website/contributing.md
+++ b/site2/website/contributing.md
@@ -252,7 +252,7 @@
>
> Git commit message is not only the best way to communicate context about code changes, but also shows whether a developer is a good collaborator. If the first commit message of a PR is not clear but the PR description is clear and concise, when merging a PR, consider copying the PR description to the commit message box or writing a proper one rather than using the default (first) commit message (see image below). In this way, others know the changes clearly, which is beneficial to cut a release or write a release note. Be well cared for git log is a healthy and sustainable thing.
-
+
### Contributor License Agreement
diff --git a/site2/website/sidebars.json b/site2/website/sidebars.json
index af39e9c..a95aead 100644
--- a/site2/website/sidebars.json
+++ b/site2/website/sidebars.json
@@ -149,7 +149,8 @@
"develop-tools",
"develop-binary-protocol",
"develop-schema",
- "develop-load-manager"
+ "develop-load-manager",
+ "develop-plugin"
],
"Reference": [
"reference-terminology",
