MyBatis generator自定义插件或者扩展报Cannot instantiate object of type XXX

Joe.Ye • 2023-03-25 • MyBatis

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，或者自定义的一些注释，作者信息等。

官方文档也说可以自定义插件，但是当我们继承或者实现mybatis-generator的类或者接口时，运行报错：

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：http://mybatis.org/generator/running/runningWithMaven.html

Classpath Issues
Initially, the plugin classpath is very limited - it only contains MyBatis generator itself. If you need to add something to the plugin's classpath (for example, a JDBC driver)

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：我们需要把自己写的插件封装成一个jar，或者安装到本地，或者deploy至项目仓库，然后在plugin中添加依赖

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>

配置示例：

<plugin>
    <groupId>org.mybatis.generator</groupId>
    <artifactId>mybatis-generator-maven-plugin</artifactId>
    <version>1.4.0</version>
    <dependencies>
        <dependency>
            <groupId>com.taozipay</groupId>
            <artifactId>union-pay-dao</artifactId>
            <version>1.0.0-SNAPSHOT</version>
            <scope>system</scope>
            <systemPath>E:/Library/MavenRepository/com/taozipay/union-pay-dao/1.0.0-SNAPSHOT/union-pay-dao-1.0.0-SNAPSHOT.jar</systemPath>
        </dependency>
        <dependency>
            <groupId>org.mybatis.generator</groupId>
            <artifactId>mybatis-generator-core</artifactId>
            <version>1.4.0</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.20</version>
        </dependency>
    </dependencies>
    <configuration>
        <verbose>true</verbose>
        <overwrite>true</overwrite>
        <configurationFile>src/main/resources/generatorConfig.xml</configurationFile>
    </configuration>
</plugin>

方案二

安装jar到本地仓库：

mvn install:install-file -DgroupId=com.taozipay -DartifactId=union-pay-dao -Dversion=1.0.0-SNAPSHOT -Dpackaging=jar -Dfile=E:/Library/MavenRepository/union-pay-dao-1.0.0-SNAPSHOT.jar -DgeneratePom=true

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

安装jar到项目：

mvn install:install-file -DgroupId=com.taozipay -DartifactId=union-pay-dao -Dversion=1.0.0-SNAPSHOT -Dpackaging=jar -Dfile=E:\Library\MavenRepository\com\taozipay\union-pay-dao\1.0.0-SNAPSHOT\union-pay-dao-1.0.0-SNAPSHOT.jar -DgeneratePom=true -DlocalRepositoryPath=E:\union-pay\union-pay-dao\src\main\resources\lib2\

然后再在plugin的pom中添加jar依赖：

<build>
  <plugins>
    <plugin>
      <repositories>
        <repository>
          <id>in-project-repo</id>
          <releases>
            <checksumPolicy>ignore</checksumPolicy>
          </releases>
          <url>file://${project.basedir}/repo</url>
        </repository>
      </repositories>
...
  <dependency>
    <groupId>xxx</groupId>
    <artifactId>xxx</artifactId>
    <version>1.0</version>
  </dependency>

版权声明：
作者：Joe.Ye
链接：https://www.appblog.cn/index.php/2023/03/25/mybatis-generator-custom-plugin-or-extension-reports-cannot-instantiate-object-of-type-xxx/
来源：APP全栈技术分享
文章版权归作者所有，未经允许请勿转载。

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MyBatis generator自定义插件或者扩展报Cannot instantiate object of type XXX
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，或者自定义的一些注释，作者信息等。 官……
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