Rename AwsLambdaAppender to StdOutAppender, plus support configuring component and environment

Author: rbygrave

README.md

@@ -4,22 +4,123 @@
 [![Discord](https://img.shields.io/discord/1074074312421683250?color=%237289da&label=discord)](https://discord.gg/Qcqf9R27BR)
 
 # avaje-logback-encoder
-logback encoder that uses avaje-jsonb to log events as json
+Logback encoder that log events as json (similar to Logstash).
 
-## Usage
+Example:
+```json
+{"timestamp":"2025-01-10T14:47:42.313+13:00","level":"INFO","logger":"org.example.Foo","message":"Hi","thread":"main"}
+```
+
+Example with component and environment:
+```json
+{"component":"my-component","env":"DEV","timestamp":"2025-01-10T14:47:42.313+13:00","level":"INFO","logger":"org.example.Foo","message":"Hi","thread":"main"}
+```
+
+## Fields
+#### Standard Fields
+- `timestamp`
+- `level`
+- `logger`
+- `message`
+- `thread`
+- `stacktrace`
+
+#### MDC Fields
+MDC key/values are included in logged events.
+
+#### Custom Fields
+Extra Custom fields can be declared in JSON form, these are added to all logged events.
+
+#### Extra recommended Fields
+- `component` - Use to define the "component" (approximately application or a specific component of an application)
+- `env` - Use to define the "environment" such as dev, test, prod etc
+
+These default by reading System Environment variables `COMPONENT` and `ENVIRONMENT` respectively and
+can also be explicitly set via configuration.
+
+
+
+# How to use
+
+#### 1 - Add dependency
+
+For Java 11+ and Logback 1.2.x+ use version `1.0` of the dependency:
+```xml
+<dependency>
+  <groupId>io.avaje</groupId>
+  <artifactId>avaje-logback-encoder</artifactId>
+  <version>1.0</version>
+</dependency>
+```
 
-Add the encoder to your appender
+For Java 8 and Logback 1.1.x use version `1.0-java8` of the dependency.
+```xml
+<dependency>
+  <groupId>io.avaje</groupId>
+  <artifactId>avaje-logback-encoder</artifactId>
+  <version>1.0-java8</version>
+</dependency>
+```
 
+#### 2 - Use the Encoder in logback.xml
+
+In `logback.xml` specify JsonEncoder as the encoder like:
 ```xml
+<appender name="app" class="your.appender.class">
+  <encoder class="io.avaje.logback.encoder.JsonEncoder"/>
+</appender>
+```
 
+Optionally, configure with `component` and `environment` like:
+```xml
 <appender name="app" class="your.appender.class">
-    <encoder class="io.avaje.logback.encoder.JsonEncoder">
-        <-- configuration -->
-    </encoder>
+  <encoder class="io.avaje.logback.encoder.JsonEncoder">
+    <component>my-component</component> <!-- OPTIONAL -->
+    <enviroment>dev</enviroment>        <!-- OPTIONAL -->
+  </encoder>
 </appender>
 ```
 
-### JPMS Use
+Optionally specify custom fields that will appear in every LoggingEvent like:
+```xml
+<encoder class="io.avaje.logback.encoder.JsonEncoder">
+  <customFields>{"appname":"myWebservice","roles":["orders","auth"]}</customFields>
+</encoder>
+```
+
+#### AWS Lambda / StdOutAppender
+
+For AWS Lambda log events are written to `System.out` and so this also provides
+an appender that defaults to using JsonEncoder to write log events to `System.out`.
+We can specify to use that appender like:
+
+```xml
+<!-- Defaults to using the JsonEncoder -->
+<appender class="io.avaje.logback.encoder.StdOutAppender"/>
+```
+
+Or with configuration options for component and environment like:
+
+```xml
+<appender class="io.avaje.logback.encoder.StdOutAppender">
+  <component>my-foo</component>
+</appender>
+```
+
+Or with an encoder (potentially a different encoder):
+
+```xml
+<appender class="io.avaje.logback.encoder.StdOutAppender">
+  <encoder class="io.avaje.logback.encoder.JsonEncoder">
+    <component>my-foo</component>
+    <environment>prod</environment>
+    <customFields>{"appname":"myWebservice","buildinfo":42, "roles":["customerorder","auth"],"f":true}</customFields>
+  </encoder>
+</appender>
+```
+
+
+## Java modules
 To ensure `jlink` correctly determines the runtime modules required, add the following to your `module-info.java`:
 
 ```java
@@ -28,18 +129,7 @@ module my.module {
 }
 ```
 
-## Global Custom Fields
-
-Add custom fields that will appear in every LoggingEvent like this :
-
-```xml
 
-<encoder class="io.avaje.logback.encoder.JsonEncoder">
-    <customFields>{"appname":"myWebservice","roles":["customerorder","auth"],"buildinfo":{"version":"Version
-        0.1.0-SNAPSHOT","lastcommit":"75473700d5befa953c45f630c6d9105413c16fe1"}}
-    </customFields>
-</encoder>
-```
 
 ## Customizing Timestamp
 
@@ -50,7 +140,6 @@ By default, timestamps are written as string values in the format specified by
 You can change the pattern like this:
 
 ```xml
-
 <encoder class="io.avaje.logback.encoder.JsonEncoder">
     <timestampPattern>yyyy-MM-dd'T'HH:mm:ss.SSS</timestampPattern>
 </encoder>
@@ -64,7 +153,6 @@ The value of the `timestampPattern` can be any of the following:
 The formatter uses the default TimeZone of the host Java platform by default. You can change it like this:
 
 ```xml
-
 <encoder class="io.avaje.logback.encoder.JsonEncoder">
     <timeZone>UTC</timeZone>
 </encoder>

src/main/java/io/avaje/logback/encoder/AwsLambdaAppender.java

@@ -0,0 +1,65 @@
+package io.avaje.logback.encoder;
+
+import ch.qos.logback.classic.spi.ILoggingEvent;
+import ch.qos.logback.core.UnsynchronizedAppenderBase;
+import ch.qos.logback.core.encoder.Encoder;
+
+import java.io.IOException;
+
+/**
+ * Appender that writes to STDOUT that defaults to using JsonEncoder.
+ */
+public final class StdOutAppender extends UnsynchronizedAppenderBase<ILoggingEvent> {
+
+  private Encoder<ILoggingEvent> encoder;
+
+  public StdOutAppender() {
+    this.encoder = new JsonEncoder();
+  }
+
+  @Override
+  protected void append(ILoggingEvent event) {
+    try {
+      System.out.write(encoder.encode(event));
+    } catch (IOException e) {
+      // NOTE: When actually running on AWS Lambda, an IOException would never happen
+      e.printStackTrace();
+    }
+  }
+
+  @Override
+  public void start() {
+    encoder.start();
+    super.start();
+  }
+
+  /**
+   * Change the encoder from the default JsonEncoder.
+   */
+  public void setEncoder(Encoder<ILoggingEvent> encoder) {
+    this.encoder = encoder;
+  }
+
+  /**
+   * Set the component on an underlying JsonEncoder otherwise throw IllegalStateException.
+   */
+  public void setComponent(String component) {
+    if (encoder instanceof JsonEncoder) {
+      ((JsonEncoder) encoder).setComponent(component);
+    } else {
+      throw new IllegalStateException("Can only set component when using JsonEncoder");
+    }
+  }
+
+  /**
+   * Set the environment on an underlying JsonEncoder otherwise throw IllegalStateException.
+   */
+  public void setEnvironment(String environment) {
+    if (encoder instanceof JsonEncoder) {
+      ((JsonEncoder) encoder).setEnvironment(environment);
+    } else {
+      throw new IllegalStateException("Can only set environment when using JsonEncoder");
+    }
+  }
+
+}

src/main/java/io/avaje/logback/encoder/StdOutAppender.java

@@ -101,7 +101,9 @@ void throwable_usingConverter() {
 
     @Test
     void awsAppender() {
-      AwsLambdaAppender appender = new AwsLambdaAppender();
+      StdOutAppender appender = new StdOutAppender();
+      appender.setComponent("my-other");
+      appender.setEnvironment("localdev");
       appender.start();
 
       appender.append(createLogEvent());