java 中的MyMetaObjectHandler
时间: 2024-01-20 14:10:16 浏览: 24
MyMetaObjectHandler是一个Java类,位于包com.jxmcloud.business.shop.config下。它实现了MyBatis Plus框架中的MetaObjectHandler接口。这个类的作用是在进行数据库操作时,自动填充指定字段的值。具体来说,在新增数据时,会自动将createTime和updateTime字段的值设置为当前时间;在更新数据时,会自动将updateTime字段的值设置为当前时间。
相关问题
nested exception is java.lang.ClassNotFoundException: com.config.MyMetaObjectHandler
This error indicates that the class `com.config.MyMetaObjectHandler` cannot be found by the Java Virtual Machine (JVM) at runtime.
There are a few possible reasons why this error might occur:
1. The class `com.config.MyMetaObjectHandler` is not present in the classpath. This could happen if the class is not included in the application's JAR or WAR file, or if the classpath is not configured correctly.
2. The class `com.config.MyMetaObjectHandler` is present in the classpath, but it is not accessible to the JVM. This could happen if the class is in a different package or module than the one that is being executed, or if the class has restricted access modifiers (e.g. private or protected).
3. The class `com.config.MyMetaObjectHandler` has a dependency on another class or library that is not present in the classpath. This could happen if the application is missing a required dependency or if the dependency is not configured correctly.
To resolve this issue, you should first verify that the class `com.config.MyMetaObjectHandler` is present in the classpath and accessible to the JVM. You can also try adding any missing dependencies to the classpath and checking that they are configured correctly. If you continue to experience this issue, you may need to seek further assistance from a developer or support team with expertise in Java development.
java MetaObjectHandler源码分析
Java中的MetaObjectHandler是Mybatis框架中用于处理实体类的公共字段的接口,它提供了在插入和更新操作时自动填充实体类的公共字段的方法。我们来看一下它的源码实现。
MetaObjectHandler接口的定义如下:
```java
public interface MetaObjectHandler {
void insertFill(MetaObject metaObject);
void updateFill(MetaObject metaObject);
}
```
该接口中定义了两个抽象方法insertFill和updateFill,这两个方法分别用于在插入和更新操作时自动填充实体类的公共字段。
MetaObject是Mybatis框架中用于封装Java对象的一个通用类,通过反射获取Java对象的属性和方法,从而实现对Java对象的读写操作。MetaObjectHandler中的insertFill和updateFill方法参数中的MetaObject对象就是Java对象的封装类,可以通过该对象来获取Java对象的属性和方法,从而实现对实体类的公共字段的填充操作。
下面是一个示例代码,演示了如何在实体类中自动填充创建时间和更新时间:
```java
public class MyMetaObjectHandler implements MetaObjectHandler {
@Override
public void insertFill(MetaObject metaObject) {
LocalDateTime now = LocalDateTime.now();
this.setFieldValByName("createTime", now, metaObject);
this.setFieldValByName("updateTime", now, metaObject);
}
@Override
public void updateFill(MetaObject metaObject) {
LocalDateTime now = LocalDateTime.now();
this.setFieldValByName("updateTime", now, metaObject);
}
}
```
在上述示例代码中,我们实现了MetaObjectHandler接口,并重写了其中的insertFill和updateFill方法。在insertFill方法中,我们获取当前时间,并通过setFieldValByName方法将其赋值给实体类的createTime和updateTime字段;在updateFill方法中,我们同样获取当前时间,并将其赋值给实体类的updateTime字段。
最后,我们需要在Mybatis的配置文件中配置MyMetaObjectHandler:
```xml
<!-- 配置自定义的MetaObjectHandler -->
<bean id="myMetaObjectHandler" class="com.example.MyMetaObjectHandler"/>
<!-- 配置全局的MetaObjectHandler -->
<mybatis:configuration>
<mybatis:defaultScriptingLanguage type="org.apache.ibatis.scripting.xmltags.XMLLanguageDriver">
<mybatis:property name="metaObjectHandler" ref="myMetaObjectHandler"/>
</mybatis:defaultScriptingLanguage>
</mybatis:configuration>
```
在上述配置文件中,我们通过id为myMetaObjectHandler的bean来配置自定义的MetaObjectHandler,然后通过属性metaObjectHandler将其注入到Mybatis的配置中。这样,我们就可以在插入和更新操作时自动填充实体类的公共字段了。
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