How to configure logback as json format
Published: 2023-10-30 07:03:17

To configure Logback to output logs in JSON format, you can use the Logstash encoder, which formats log events as JSON objects. Here's how to configure Logback to output logs in JSON format:

1. **Add Logback Dependencies**: Ensure that you have the necessary dependencies in your project. Include `logback-classic` and `logstash-logback-encoder` in your Maven or Gradle build file, or download the JAR files manually.

   For Maven, add these dependencies to your `pom.xml`:

   ```xml
   <dependencies>
     <!-- Logback Classic -->
     <dependency>
       <groupId>ch.qos.logback</groupId>
       <artifactId>logback-classic</artifactId>
       <version>2.0.0</version> <!-- Use the latest version -->
     </dependency>

     <!-- Logstash Logback Encoder -->
     <dependency>
       <groupId>net.logstash.logback</groupId>
       <artifactId>logstash-logback-encoder</artifactId>
       <version>6.6</version> <!-- Use the latest version -->
     </dependency>
   </dependencies>
   ```

2. **Create a Logback Configuration File**: Create a `logback.xml` configuration file in your project's classpath. This file will specify the log format and layout.

3. **Configure Logback with JSON Encoder**:

   Inside your `logback.xml`, configure Logback to use the Logstash encoder. Here's a sample configuration:

   ```xml
   <?xml version="1.0" encoding="UTF-8"?>
   <configuration>
     <appender name="console" class="ch.qos.logback.core.ConsoleAppender">
       <encoder class="net.logstash.logback.encoder.LogstashEncoder">
         <fieldNames>
           <timestamp>timestamp</timestamp>
           <version>version</version>
           <message>message</message>
         </fieldNames>
       </encoder>
     </appender>

     <root level="INFO">
       <appender-ref ref="console"/>
     </root>
   </configuration>
   ```

   In this configuration:
   - We define an appender named "console" that logs to the console.
   - We use the `LogstashEncoder` to format logs as JSON objects.
   - Inside the `fieldNames` section, you can specify how you want log fields to be named in the JSON output. The example above maps `timestamp`, `version`, and `message` fields.

4. **Log Messages in Your Code**:

   In your Java code, use a logging framework like SLF4J with Logback bindings to log messages. For example:

   ```java
   import org.slf4j.Logger;
   import org.slf4j.LoggerFactory;

   public class MyService {
     private static final Logger logger = LoggerFactory.getLogger(MyService.class);

     public void doSomething() {
       // Log a message
       logger.info("This is an info message.");
     }
   }
   ```

5. **Run Your Application**: When you run your application, Logback will format log events as JSON and send them to the specified output (in this case, the console).

With this configuration, your application will produce logs in JSON format, which can be easily ingested by log aggregation tools, including Elasticsearch, Logstash, and Kibana (ELK stack), for further analysis and visualization.

Here's an example of what log messages would look like when using the Logback configuration I provided earlier, along with the Java code:

Assuming you have a class `MyService` as described earlier:

```java
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class MyService {
   private static final Logger logger = LoggerFactory.getLogger(MyService.class);

   public void doSomething() {
      // Log an info message
      logger.info("This is an info message.");
      
      // Log an error message
      logger.error("This is an error message.");
   }
}
```

When you call the `doSomething()` method, Logback will format log events as JSON. Here's what the log messages might look like in JSON format:

```json
{"@timestamp":"2023-09-20T12:00:00.123Z","@version":"1","message":"This is an info message.","logger_name":"com.example.MyService","thread_name":"main","level":"INFO","level_value":20000}
{"@timestamp":"2023-09-20T12:00:01.456Z","@version":"1","message":"This is an error message.","logger_name":"com.example.MyService","thread_name":"main","level":"ERROR","level_value":40000}
```

In the JSON log messages:

- `@timestamp` represents the timestamp when the log event occurred.
- `@version` indicates the log format version (usually "1").
- `message` contains the log message itself.
- `logger_name` shows the name of the logger, which is typically the class name.
- `thread_name` displays the name of the thread that generated the log event.
- `level` specifies the log level (e.g., INFO or ERROR).
- `level_value` is the numeric value associated with the log level (e.g., 20000 for INFO and 40000 for ERROR).

These log messages in JSON format are structured and suitable for ingestion into log aggregation and analysis tools, such as Elasticsearch and Kibana. You can easily search, filter, and visualize these logs in such tools to monitor and troubleshoot your application.