MyBatis使用过程中踩过的坑（一）
使用 tk.mybatis 准备生成继承通用Mapper的Dao、Entity和Mapper文件时，
运行mybatis-generator报了如下错误：
[INFO] Error stacktraces are turned on.
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building base Maven Webapp 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- mybatis-generator-maven-plugin:1.3.5:generate (default-cli) @ base ---
[INFO] Connecting to the Database
[INFO] Introspecting table s_user
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.561 s
[INFO] Finished at: 2018-06-07T21:25:42+08:00
[INFO] Final Memory: 13M/155M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.mybatis.generator:mybatis-generator-maven-plugin:1.3.5:generate (default-cli) on project base: Execution default-cli of goal org.mybatis.generator:mybatis-generator-maven-plugin:1.3.5:generate failed: Cannot instantiate object of type tk.mybatis.mapper.generator.MapperPlugin -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.mybatis.generator:mybatis-generator-maven-plugin:1.3.5:generate (default-cli) on project base: Execution default-cli of goal org.mybatis.generator:mybatis-generator-maven-plugin:1.3.5:generate failed: Cannot instantiate object of type tk.mybatis.mapper.generator.MapperPlugin
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:212)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:116)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:80)
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:307)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:193)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:106)
at org.apache.maven.cli.MavenCli.execute(MavenCli.java:863)
at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:288)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:199)
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:497)
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:1.3.5:generate failed: Cannot instantiate object of type tk.mybatis.mapper.generator.MapperPlugin
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:145)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:207)
... 21 more
Caused by: java.lang.RuntimeException: Cannot instantiate object of type tk.mybatis.mapper.generator.MapperPlugin
at org.mybatis.generator.internal.ObjectFactory.createInternalObject(ObjectFactory.java:229)
at org.mybatis.generator.internal.ObjectFactory.createPlugin(ObjectFactory.java:284)
at org.mybatis.generator.config.Context.generateFiles(Context.java:704)
at org.mybatis.generator.api.MyBatisGenerator.generate(MyBatisGenerator.java:269)
at org.mybatis.generator.api.MyBatisGenerator.generate(MyBatisGenerator.java:189)
at org.mybatis.generator.maven.MyBatisGeneratorMojo.execute(MyBatisGeneratorMojo.java:199)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:134)
... 22 more
Caused by: java.lang.ClassNotFoundException: tk.mybatis.mapper.generator.MapperPlugin
at org.codehaus.plexus.classworlds.strategy.SelfFirstStrategy.loadClass(SelfFirstStrategy.java:50)
at org.codehaus.plexus.classworlds.realm.ClassRealm.unsynchronizedLoadClass(ClassRealm.java:271)
at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:247)
at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:239)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at org.mybatis.generator.internal.ObjectFactory.internalClassForName(ObjectFactory.java:181)
at org.mybatis.generator.internal.ObjectFactory.createInternalObject(ObjectFactory.java:225)
... 28 more
[ERROR]
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/PluginExecutionException1、org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.mybatis.generator:mybatis-generator-maven-plugin:1.3.5:generate (default-cli) on project base: Execution default-cli of goal org.mybatis.generator:mybatis-generator-maven-plugin:1.3.5:generate failed: Cannot instantiate object of type tk.mybatis.mapper.generator.MapperPlugin；
2、org.apache.maven.plugin.PluginExecutionException: Execution default-cli of goal org.mybatis.generator:mybatis-generator-maven-plugin:1.3.5:generate failed: Cannot instantiate object of type tk.mybatis.mapper.generator.MapperPlugin；
3、java.lang.RuntimeException: Cannot instantiate object of type tk.mybatis.mapper.generator.MapperPlugin；
4、java.lang.ClassNotFoundException: tk.mybatis.mapper.generator.MapperPlugin。经度娘一波，发现网上提供的解决办法有以下几种：
1、把mybatis-generator.xml配置文件中的 javaClientGenerator标签里的type赋值"XMLMAPPER"或"ANNOTATEDMAPPER"，仔细检查后这条排除；
2、更新org.mybatis.mapper.generator.MapperPlugin这个插件的版本，但把 tk.mybatis:mapper从v3.3.6升级到v3.4.6后问题依旧存在，这条排除；
后来发现报错信息里出现"ClassNotFoundException"，在思考会不会是maven导入的包mybatis-generator没有找到，所以尝试调换依赖的位置：
调换前-->
org.mybatis.generator
mybatis-generator-maven-plugin
1.3.5
true
true
src/main/resources/mybatis/generator-config.xml
调换后-->
org.mybatis.generator
mybatis-generator-maven-plugin
1.3.5
true
true
src/main/resources/mybatis/generator-config.xml
org.mybatis.generator
mybatis-generator-core
1.3.5
tk.mybatis
mapper
3.4.6
结果再次运行mybatis-generator成功生成文件
[INFO] Error stacktraces are turned on.
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building base Maven Webapp 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- mybatis-generator-maven-plugin:1.3.5:generate (default-cli) @ base ---
[INFO] Connecting to the Database
[INFO] Introspecting table s_user
[INFO] Generating Record class for table s_user
[INFO] Generating Mapper Interface for table s_user
[INFO] Generating SQL Map for table s_user
[INFO] Saving file UserMapper.xml
[INFO] Saving file User.java
[INFO] Saving file UserMapper.java
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.134 s
[INFO] Finished at: 2018-06-07T22:24:19+08:00
[INFO] Final Memory: 13M/220M
[INFO] ------------------------------------------------------------------------