title: Spring Boot - logback PARSER_ERROR
body: <p>I am using Spring Boot 1.2.0 and the below logback.xml file but for some reason, I see log lines that start like this. What is this PARSER_ERROR[wex]? Any idea? Completely removing logback.xml makes the PARSER_ERROR[wex] go away but the lig file has the literal "${PID:- }" logged instead of the PID</p>
  
  <pre><code>%PARSER_ERROR[wex]2014-12-30 12:25:25.730  INFO 77114 [localhost-startStop-1]
  </code></pre>
  
  <p>logback.xml</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;configuration&gt;
  
  
      &lt;property name="LOG_FILE" value="${LOG_FILE:-${LOG_PATH:-${LOG_TEMP:-${java.io.tmpdir:-/tmp}}/}spring.log}"/&gt;
      &lt;property name="FILE_LOG_PATTERN" value="%d{yyyy-MM-dd HH:mm:ss.SSS} %5p ${PID:- } [%t] --- %-40.40logger{39} : %m%n%wex"/&gt;
  
      &lt;appender name="FILE"
                class="ch.qos.logback.core.rolling.RollingFileAppender"&gt;
          &lt;encoder&gt;
              &lt;pattern&gt;${FILE_LOG_PATTERN}&lt;/pattern&gt;
          &lt;/encoder&gt;
          &lt;file&gt;${LOG_FILE}&lt;/file&gt;
          &lt;rollingPolicy class="ch.qos.logback.core.rolling.FixedWindowRollingPolicy"&gt;
              &lt;fileNamePattern&gt;${LOG_FILE}.%i&lt;/fileNamePattern&gt;
          &lt;/rollingPolicy&gt;
          &lt;triggeringPolicy
                  class="ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy"&gt;
              &lt;MaxFileSize&gt;10MB&lt;/MaxFileSize&gt;
          &lt;/triggeringPolicy&gt;
      &lt;/appender&gt;
  
      &lt;root level="INFO"&gt;
          &lt;appender-ref ref="FILE" /&gt;
      &lt;/root&gt;
  
  &lt;/configuration&gt;
  </code></pre>
  
  <p>Digging into the source, I see wex as a conversionRule over <a href="https://github.com/spring-projects/spring-boot/blob/v1.2.0.RELEASE/spring-boot/src/main/resources/org/springframework/boot/logging/logback/defaults.xml" rel="nofollow">here</a> but I am not sure what it is doing or how a PARSER_ERROR is happening. I am trying to dig deeper but if I am doing something obviously wrong, please let me know.</p>
  
  <hr>
  
  <p><strong>Update 1:</strong></p>
  
  <p>Adding the line</p>
  
  <pre><code>&lt;conversionRule conversionWord="wex" converterClass="org.springframework.boot.logging.logback.WhitespaceThrowableProxyConverter" /&gt;
  </code></pre>
  
  <p>in the logback.xml file seems to have fixed it. The strange thing is, I have to explicitly add the conversionRule even if I include the defaults.xml explicitly. Why?</p>
  
  <hr>