title: How to change standard fields names in logback LogstashSocketAppender?
body: <p>In my Spring backend: standard log fields names are: <strong>"message"</strong> and <strong>"level"</strong> and logback.xml file works great:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;configuration scan="true" scanPeriod="5 seconds"&gt;
      &lt;property resource="application.properties"/&gt;
      &lt;appender name="stdout" class="ch.qos.logback.core.ConsoleAppender"&gt;
          &lt;encoder class="ch.qos.logback.classic.encoder.PatternLayoutEncoder"&gt;
              &lt;Pattern&gt;[%d{yyyy-MM-dd HH:mm:ss.SSS}] &lt;%-5level&gt; [Backend] &lt;%thread&gt; &amp;msg%n
              &lt;/Pattern&gt;
          &lt;/encoder&gt;
      &lt;/appender&gt;
  
      &lt;root level="DEBUG"&gt;
          &lt;appender-ref ref="stdout"/&gt;
      &lt;/root&gt;
  &lt;/configuration&gt;
  </code></pre>
  
  <p><strong>Question:</strong>
  How to change standard log field names using <strong>LogstashSocketAppender</strong> from "<strong>message</strong>" to "<strong>log-message</strong>"?</p>
  
  <p>I already try add this appender:</p>
  
  <pre><code>&lt;appender name="stash" class="net.logstash.logback.appender.LogstashSocketAppender"&gt;
      &lt;host&gt;localhost&lt;/host&gt;
      &lt;port&gt;6002&lt;/port&gt;
      &lt;customFields&gt;
          {
          "timestamp":"%d{yyyy-MM-dd HH:mm:ss.SSS}",
          "component": "Backend",
          "log-message": "%msg",
          "log-level": "%-5level"
          }&lt;/customFields&gt;
  &lt;/appender&gt;
  </code></pre>
  
  <p>but my outpust looks like this:</p>
  
  <pre><code>{
  "message":"correct log message here"
  "log-message":"%msg" &lt;--- BAD VALUE
  </code></pre>