CDC Connectors for Apache Flink<sup>®</sup> is a set of source connectors for <ahref="https://flink.apache.org/">Apache Flink<sup>®</sup></a>, ingesting changes from different databases using change data capture (CDC).
The CDC Connectors for Apache Flink<sup>®</sup> integrate Debezium as the engine to capture data changes. So it can fully leverage the ability of Debezium. See more about what is [Debezium](https://github.com/debezium/debezium).
The example shows how to create a MySQL CDC source in [Flink SQL Client](https://nightlies.apache.org/flink/flink-docs-stable/docs/dev/table/sqlclient/) and execute queries on it.
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In some cases, users can use the `JsonDebeziumDeserializationSchema(true)` Constructor to enabled include schema in the message. Then the Debezium JSON message may look like this:
The `JsonDebeziumDeserializationSchema` can also accept custom configuration of `JsonConverter`, for example if you want to obtain numeric output for decimal data,
you can construct `JsonDebeziumDeserializationSchema` as following:
```java
Map<String,Object> customConverterConfigs = new HashMap<>();
You need to install the google-java-format plugin. Spotless together with google-java-format is used to format the codes.
It is recommended to automatically format your code by applying the following settings:
1. Go to "Settings" → "Other Settings" → "google-java-format Settings".
2. Tick the checkbox to enable the plugin.
3. Change the code style to "Android Open Source Project (AOSP) style".
4. Go to "Settings" → "Tools" → "Actions on Save".
5. Under "Formatting Actions", select "Optimize imports" and "Reformat file".
6. From the "All file types list" next to "Reformat code", select "Java".
For earlier IntelliJ IDEA versions, the step 4 to 7 will be changed as follows.
- 4.Go to "Settings" → "Other Settings" → "Save Actions".
- 5.Under "General", enable your preferred settings for when to format the code, e.g. "Activate save actions on save".
- 6.Under "Formatting Actions", select "Optimize imports" and "Reformat file".
- 7.Under "File Path Inclusions", add an entry for `.*\.java` to avoid formatting other file types.
Then the whole project could be formatted by command `mvn spotless:apply`.
#### Checkstyle
Checkstyle is used to enforce static coding guidelines.
1. Go to "Settings" → "Tools" → "Checkstyle".
2. Set "Scan Scope" to "Only Java sources (including tests)".
3. For "Checkstyle Version" select "8.14".
4. Under "Configuration File" click the "+" icon to add a new configuration.
5. Set "Description" to "Flink cdc".
6. Select "Use a local Checkstyle file" and link it to the file `tools/maven/checkstyle.xml` which is located within your cloned repository.
7. Select "Store relative to project location" and click "Next".
8. Configure the property `checkstyle.suppressions.file` with the value `suppressions.xml` and click "Next".
9. Click "Finish".
10. Select "Flink cdc" as the only active configuration file and click "Apply".
You can now import the Checkstyle configuration for the Java code formatter.
1. Go to "Settings" → "Editor" → "Code Style" → "Java".
2. Click the gear icon next to "Scheme" and select "Import Scheme" → "Checkstyle Configuration".
3. Navigate to and select `tools/maven/checkstyle.xml` located within your cloned repository.
Then you could click "View" → "Tool Windows" → "Checkstyle" and find the "Check Module" button in the opened tool window to validate checkstyle. Or you can use the command `mvn clean compile checkstyle:checkstyle` to validate.
### Documentation Contribute
Flink cdc documentations locates at `docs/content`.
The contribution step is the same as the code contribution. We use markdown as the source code of the document.
