title: QueryDSL generated classes keep getting deleted in maven project in Spring Tool Suite
body: <p>I am using QueryDSL in a maven Spring Boot project in Eclipse, with Spring DevTools activated, and everything works fine, except for the fact that the QClass used in QueryDSL get deleted, and next time I try to relaunch the project (or it tries to auto-reload through Spring DevTools) I get an error, and I must go through "Run as"->"Maven generate-sources" again.
  I am not sure what exactly triggers the deletion, but I noticed that for instance adding or removing a file will trigger the deletion. Removing DevTools didn't help.</p>
  
  <p>Is there a way to prevent those constant deletion, or to make sure that the classes are automatically regenerated afterward?</p>
  
  <p>Here are the relevant part of my pom.xml :</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"&gt;
      &lt;modelVersion&gt;4.0.0&lt;/modelVersion&gt;
      &lt;parent&gt;
          &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
          &lt;artifactId&gt;spring-boot-starter-parent&lt;/artifactId&gt;
          &lt;version&gt;2.1.2.RELEASE&lt;/version&gt;
          &lt;relativePath/&gt; &lt;!-- lookup parent from repository --&gt;
      &lt;/parent&gt;
      &lt;groupId&gt;REDACTED&lt;/groupId&gt;
      &lt;artifactId&gt;REDACTED&lt;/artifactId&gt;
      &lt;version&gt;0.0.1-SNAPSHOT&lt;/version&gt;
      &lt;name&gt;REDACTED&lt;/name&gt;
      &lt;description&gt;REDACTED&lt;/description&gt;
  
      &lt;properties&gt;
          &lt;java.version&gt;11&lt;/java.version&gt;
      &lt;/properties&gt;
  
      &lt;dependencies&gt;
      [...]
          &lt;dependency&gt;
              &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
              &lt;artifactId&gt;spring-boot-starter-data-jpa&lt;/artifactId&gt;
          &lt;/dependency&gt;
      [...]
          &lt;dependency&gt;
              &lt;groupId&gt;mysql&lt;/groupId&gt;
              &lt;artifactId&gt;mysql-connector-java&lt;/artifactId&gt;
              &lt;scope&gt;runtime&lt;/scope&gt;
          &lt;/dependency&gt;
          &lt;dependency&gt;
              &lt;groupId&gt;com.querydsl&lt;/groupId&gt;
              &lt;artifactId&gt;querydsl-core&lt;/artifactId&gt;
          &lt;/dependency&gt;
          &lt;dependency&gt;
              &lt;groupId&gt;com.querydsl&lt;/groupId&gt;
              &lt;artifactId&gt;querydsl-jpa&lt;/artifactId&gt;
          &lt;/dependency&gt;
      &lt;/dependencies&gt;
  
      &lt;build&gt;
          &lt;plugins&gt;
              &lt;plugin&gt;
                  &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
                  &lt;artifactId&gt;spring-boot-maven-plugin&lt;/artifactId&gt;
              &lt;/plugin&gt;
              &lt;plugin&gt;
                  &lt;groupId&gt;com.mysema.maven&lt;/groupId&gt;
                  &lt;artifactId&gt;apt-maven-plugin&lt;/artifactId&gt;
                  &lt;version&gt;1.1.3&lt;/version&gt;
                  &lt;executions&gt;
                      &lt;execution&gt;
                          &lt;goals&gt;
                              &lt;goal&gt;process&lt;/goal&gt;
                          &lt;/goals&gt;
                          &lt;configuration&gt;
                              &lt;outputDirectory&gt;target/generated-sources/customfolder&lt;/outputDirectory&gt;
                              &lt;clearOutputDir&gt;false&lt;/clearOutputDir&gt;
                              &lt;processor&gt;com.querydsl.apt.jpa.JPAAnnotationProcessor&lt;/processor&gt;
                          &lt;/configuration&gt;
                      &lt;/execution&gt;
                  &lt;/executions&gt;
                  &lt;dependencies&gt;
                      &lt;dependency&gt;
                          &lt;groupId&gt;com.querydsl&lt;/groupId&gt;
                          &lt;artifactId&gt;querydsl-apt&lt;/artifactId&gt;
                          &lt;version&gt;${querydsl.version}&lt;/version&gt;
                      &lt;/dependency&gt;
                  &lt;/dependencies&gt;
              &lt;/plugin&gt;
              &lt;plugin&gt;
                  &lt;groupId&gt;org.codehaus.mojo&lt;/groupId&gt;
                  &lt;artifactId&gt;build-helper-maven-plugin&lt;/artifactId&gt;
                  &lt;executions&gt;
                      &lt;execution&gt;
                          &lt;id&gt;add-source&lt;/id&gt;
                          &lt;phase&gt;generate-sources&lt;/phase&gt;
                          &lt;goals&gt;
                              &lt;goal&gt;add-source&lt;/goal&gt;
                          &lt;/goals&gt;
                          &lt;configuration&gt;
                              &lt;sources&gt;
                                  &lt;source&gt;${project.build.directory}/generated-sources/customfolder/&lt;/source&gt;
                              &lt;/sources&gt;
                          &lt;/configuration&gt;
                      &lt;/execution&gt;
                  &lt;/executions&gt;
              &lt;/plugin&gt;
          &lt;/plugins&gt;
      &lt;/build&gt;
  
  &lt;/project&gt;
  </code></pre>