1、错误说明
mybatis generator确实好用，但是离我们的生产代码还是有差别的
比如缺少，toString hashCode equals等方法，或者自定一的一些注释，作者信息等。
官方文档也说可以自定义插件，但是当我们满心欢喜的继承或者实现了mybatis-generator的类或者接口的时候，已运行，报错了，并且我们有默认的空构造。报错如下：
Failed to execute goal org.mybatis.generator:mybatis-generator-maven-plugin:1.3.6:generate (default-cli) on project damon: Execution default-cli of goal org.mybatis.generator:mybatis-generator-maven-plugin:1.3.6:generate failed: Cannot instantiate object of type cn.edu.zua.damon.util.MyDefaultCommentGenerator -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.mybatis.generator:mybatis-generator-maven-plugin:1.3.6:generate (default-cli) on project damon: Execution default-cli of goal org.mybatis.generator:mybatis-generator-maven-plugin:1.3.6:generate failed: Cannot instantiate object of type cn.edu.zua.damon.util.MyDefaultCommentGenerator
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:213)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:154)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:146)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:51)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:309)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:194)
at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:107)
at org.apache.maven.cli.MavenCli.execute (MavenCli.java:955)
at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:290)
at org.apache.maven.cli.MavenCli.main (MavenCli.java:194)
at sun.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke (Method.java:498)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:289)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:229)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:415)
at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:356)
at org.codehaus.classworlds.Launcher.main (Launcher.java:47)
Caused by: org.apache.maven.plugin.PluginExecutionException: Execution default-cli of goal org.mybatis.generator:mybatis-generator-maven-plugin:1.3.6:generate failed: Cannot instantiate object of type cn.edu.zua.damon.util.MyDefaultCommentGenerator
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:145)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:208)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:154)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:146)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:51)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:309)
at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:194)
at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:107)
at org.apache.maven.cli.MavenCli.execute (MavenCli.java:955)
at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:290)经过耐心的搜索和寻找，大致确定了错误。
错误就是，mybatis-generator 的plugin有自己的classpath，我们在项目中直接继承的类和plugin不属于同一个classpath。这一点在官方文档有一点提到，
但是官方文档并没有明确说明，当我们自定义的插件该放到哪里。
到这里，问题就解决了。
我们需要吧自己写的插件封装成一个jar，然后在plugin中添加依赖，或者安装到本地，或者项目仓库。
2、解决方案
方案一
在plugin的pom中添加jar依赖
<dependency>
<groupId>xxx</groupId>
<artifactId>xxx</artifactId>
<version>1.0</version>
<scope>system</scope>
<systemPath>F:/xxx/lib/xxx.jar</systemPath>
</dependency>方案二
使用：https://blog.csdn.net/u_ascend/article/details/80485931 中的命令安装jar到本地仓库，然后再在plugin的pom中添加jar依赖
<dependency>
<groupId>xxx</groupId>
<artifactId>xxx</artifactId>
<version>1.0</version>
</dependency>方案三
和方案二类似，这种方案的区别是仓库位于项目下。安装命令也是使用 https://blog.csdn.net/u_ascend/article/details/80485931 中的命令安装jar到项目仓库，然后再在plugin的pom中添加jar依赖。
<repositories>
<repository>
<id>in-project-repo</id>
<releases>
<checksumPolicy>ignore</checksumPolicy>
</releases>
<url>file://${project.basedir}/repo</url>
</repository>
</repositories>
...
<build>
...
...
<dependency>
<groupId>xxx</groupId>
<artifactId>xxx</artifactId>
<version>1.0</version>
</dependency>