Configuring Logback for Custom Log Format | Generated by AI

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To achieve the log format you provided, you’ll need to configure your logback.xml file. The key is to use a PatternLayout within your appender and set the pattern property correctly.

Here’s a breakdown of the components in your desired log format and how to map them to Logback pattern converters:

• 2025-06-15T01:37:52.452+08:00: This is the timestamp. You’ll use %d{yyyy-MM-dd'T'HH:mm:ss.SSSXXX} for this.
  • yyyy-MM-dd'T'HH:mm:ss.SSS: Date and time with milliseconds.
  • XXX: ISO 8601 offset from UTC (e.g., +08:00).
• DEBUG: This is the logging level. You’ll use %-5p (left-aligned, 5 characters wide).
• 302244: This is the process ID. Logback doesn’t directly expose the process ID in its standard converters. However, it does expose the thread ID (%t or %thread). If “302244” in your example is actually a thread ID (which is very common in application logs), then %thread is what you need. If it must be the OS process ID, you might need a custom Logback converter or a system property if your environment allows. For typical Spring Boot applications, this is usually the thread ID. I’ll assume it’s the thread ID for this example.
• ---: A literal string.
• [nio-8090-exec-1]: This is the thread name. You’ll use [%thread] or %-40.40thread if you want it fixed width.
• o.s.w.s.m.m.a.HttpEntityMethodProcessor: This is the logger name (typically the fully qualified class name). You’ll use %-40.40logger{39} to get a right-aligned, truncated logger name up to 39 characters.
• :: A literal colon.
• Writing ["{"vnstatversion":"2.9","jsonversion":"2","interfaces":[{"name":"enp4s0","alias":"","created":{"date" (truncated)..."]: This is the log message. You’ll use %msg%n.

Here’s a sample logback.xml configuration that should produce a very similar output:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>

    <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>%d{yyyy-MM-dd'T'HH:mm:ss.SSSXXX} %highlight(%-5p) %thread --- [%thread] %-40.40logger{39} : %msg%n</pattern>
        </encoder>
    </appender>

    <root level="INFO">
        <appender-ref ref="CONSOLE"/>
    </root>

    <logger name="org.springframework.web.servlet.mvc.method.annotation.HttpEntityMethodProcessor" level="DEBUG"/>
    <logger name="org.springframework.web.servlet.DispatcherServlet" level="DEBUG"/>

</configuration>

Explanation of the pattern:

• %d{yyyy-MM-dd'T'HH:mm:ss.SSSXXX}: Date and time in ISO 8601 format with milliseconds and timezone offset.
• %highlight(%-5p): This will output the logging level (e.g., DEBUG, INFO) left-aligned in 5 characters, and if you’re outputting to a console, Logback will attempt to colorize it.
• %thread: The name of the thread that logged the event. (If you need the process ID, it’s more complex, but for Spring apps, thread ID is usually what’s relevant here).
• ---: A literal string separator.
• [%thread]: The thread name enclosed in square brackets.
• %-40.40logger{39}: The name of the logger (usually the class name).
  • %-40: Left-aligned and padded to 40 characters.
  • .40logger: Truncates the logger name if it’s longer than 40 characters.
  • {39}: This tells Logback to display at most 39 characters of the logger name, starting from the end of the package name (e.g., o.s.w.s.m.m.a.HttpEntityMethodProcessor might become o.s.w.s.m.m.a.HttpEntityMethodProcessor if it fits, or ...HttpEntityMethodProcessor if truncated from the beginning). You can adjust this number.
• ` : `: A literal colon and space.
• %msg%n: The actual log message followed by a new line.

Important Notes:

1. Placement: Save this XML as logback.xml in your src/main/resources directory of your Spring Boot project.
2. Process ID vs. Thread ID: As mentioned, Logback’s standard pattern converters don’t expose the OS process ID directly. If 302244 must be the process ID, you’d typically have to implement a custom PatternLayoutConverter or set a system property at startup that you then reference in your logback pattern. However, for most application logging, the thread ID (%thread) is sufficient and commonly used in this position.
3. Spring Boot Defaults: Spring Boot often provides its own default Logback configuration if you don’t provide one. By placing logback.xml in src/main/resources, you override the default.
4. Logger Levels: Make sure the specific loggers (like HttpEntityMethodProcessor and DispatcherServlet) are set to DEBUG level if you want to see their DEBUG messages. If the root level is INFO, then by default, DEBUG messages won’t be shown unless you explicitly set the level for specific loggers.

This configuration should get you very close to your desired log format.

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