网站开发一定要用框架嘛,wordpress背景图片,网站流量30g,在网站中添加搜索引擎前言 本篇需要对于MyBatis有一定的认识#xff0c;而且只是针对于TypeHandler接口来讨论#xff0c;暂不讨论其他方面的问题 TypeHandler概叙 TypeHandler是MyBatis设计的一个用于参数的接口#xff0c;你们会不会很好奇MyBatis是如何把整形#xff0c;时间#xff0c;字符…前言 本篇需要对于MyBatis有一定的认识而且只是针对于TypeHandler接口来讨论暂不讨论其他方面的问题 TypeHandler概叙 TypeHandler是MyBatis设计的一个用于参数的接口你们会不会很好奇MyBatis是如何把整形时间字符串等映射到数据表字段的实际上就是这个接口来做的在TypeHandlerRegistry的构造器中初始化了很多处理器如下 public TypeHandlerRegistry(Configuration configuration) {this.unknownTypeHandler new UnknownTypeHandler(configuration);register(Boolean.class, new BooleanTypeHandler());register(boolean.class, new BooleanTypeHandler());register(JdbcType.BOOLEAN, new BooleanTypeHandler());register(JdbcType.BIT, new BooleanTypeHandler());register(Byte.class, new ByteTypeHandler());register(byte.class, new ByteTypeHandler());register(JdbcType.TINYINT, new ByteTypeHandler());register(Short.class, new ShortTypeHandler());register(short.class, new ShortTypeHandler());register(JdbcType.SMALLINT, new ShortTypeHandler());register(Integer.class, new IntegerTypeHandler());register(int.class, new IntegerTypeHandler());register(JdbcType.INTEGER, new IntegerTypeHandler());register(Long.class, new LongTypeHandler());register(long.class, new LongTypeHandler());register(Float.class, new FloatTypeHandler());register(float.class, new FloatTypeHandler());register(JdbcType.FLOAT, new FloatTypeHandler());register(Double.class, new DoubleTypeHandler());register(double.class, new DoubleTypeHandler());register(JdbcType.DOUBLE, new DoubleTypeHandler());register(Reader.class, new ClobReaderTypeHandler());register(String.class, new StringTypeHandler());register(String.class, JdbcType.CHAR, new StringTypeHandler());register(String.class, JdbcType.CLOB, new ClobTypeHandler());register(String.class, JdbcType.VARCHAR, new StringTypeHandler());register(String.class, JdbcType.LONGVARCHAR, new StringTypeHandler());register(String.class, JdbcType.NVARCHAR, new NStringTypeHandler());register(String.class, JdbcType.NCHAR, new NStringTypeHandler());register(String.class, JdbcType.NCLOB, new NClobTypeHandler());register(JdbcType.CHAR, new StringTypeHandler());register(JdbcType.VARCHAR, new StringTypeHandler());register(JdbcType.CLOB, new ClobTypeHandler());register(JdbcType.LONGVARCHAR, new StringTypeHandler());register(JdbcType.NVARCHAR, new NStringTypeHandler());register(JdbcType.NCHAR, new NStringTypeHandler());register(JdbcType.NCLOB, new NClobTypeHandler());register(Object.class, JdbcType.ARRAY, new ArrayTypeHandler());register(JdbcType.ARRAY, new ArrayTypeHandler());register(BigInteger.class, new BigIntegerTypeHandler());register(JdbcType.BIGINT, new LongTypeHandler());register(BigDecimal.class, new BigDecimalTypeHandler());register(JdbcType.REAL, new BigDecimalTypeHandler());register(JdbcType.DECIMAL, new BigDecimalTypeHandler());register(JdbcType.NUMERIC, new BigDecimalTypeHandler());register(InputStream.class, new BlobInputStreamTypeHandler());register(Byte[].class, new ByteObjectArrayTypeHandler());register(Byte[].class, JdbcType.BLOB, new BlobByteObjectArrayTypeHandler());register(Byte[].class, JdbcType.LONGVARBINARY, new BlobByteObjectArrayTypeHandler());register(byte[].class, new ByteArrayTypeHandler());register(byte[].class, JdbcType.BLOB, new BlobTypeHandler());register(byte[].class, JdbcType.LONGVARBINARY, new BlobTypeHandler());register(JdbcType.LONGVARBINARY, new BlobTypeHandler());register(JdbcType.BLOB, new BlobTypeHandler());register(Object.class, unknownTypeHandler);register(Object.class, JdbcType.OTHER, unknownTypeHandler);register(JdbcType.OTHER, unknownTypeHandler);register(Date.class, new DateTypeHandler());register(Date.class, JdbcType.DATE, new DateOnlyTypeHandler());register(Date.class, JdbcType.TIME, new TimeOnlyTypeHandler());register(JdbcType.TIMESTAMP, new DateTypeHandler());register(JdbcType.DATE, new DateOnlyTypeHandler());register(JdbcType.TIME, new TimeOnlyTypeHandler());register(java.sql.Date.class, new SqlDateTypeHandler());register(java.sql.Time.class, new SqlTimeTypeHandler());register(java.sql.Timestamp.class, new SqlTimestampTypeHandler());register(String.class, JdbcType.SQLXML, new SqlxmlTypeHandler());register(Instant.class, new InstantTypeHandler());register(LocalDateTime.class, new LocalDateTimeTypeHandler());register(LocalDate.class, new LocalDateTypeHandler());register(LocalTime.class, new LocalTimeTypeHandler());register(OffsetDateTime.class, new OffsetDateTimeTypeHandler());register(OffsetTime.class, new OffsetTimeTypeHandler());register(ZonedDateTime.class, new ZonedDateTimeTypeHandler());register(Month.class, new MonthTypeHandler());register(Year.class, new YearTypeHandler());register(YearMonth.class, new YearMonthTypeHandler());register(JapaneseDate.class, new JapaneseDateTypeHandler());// issue #273register(Character.class, new CharacterTypeHandler());register(char.class, new CharacterTypeHandler());} 所以我们平时不用设计什么就可以进行自动转换而一种特殊情况下我们需要自己定义也就是枚举这也是我们经常用的技术比如有以下的对象 public class SysUser {/*** 用户名*/private String name;/*** 密码-加密模式*/private String password;/*** 数据状态,0-正常,1-删除*/private DataStateEnum deleted DataStateEnum.NORMAL;
}package com.zxc.movie.common.enums;/*** 数据状态*/
public enum DataStateEnum implements BaseEnumDataStateEnum{NORMAL(0, 正常),DELETE(1, 删除),;private final Integer code;private final String desc;DataStateEnum(Integer code, String desc) {this.code code;this.desc desc;}Overridepublic Integer getCode() {return code;}Overridepublic String getDesc() {return desc;}
}那么我们如何进行转换呢其实有很多种方式下面一个个说下
常规方式 直接继承BaseTypeHandler然后实现就行看下面的描述就很简单了 package com.zxc.movie.common.typehandler.common;import com.zxc.movie.common.enums.BaseEnumUtils;
import com.zxc.movie.common.enums.DataStateEnum;
import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Objects;/**
* author zxc_user
* date 2023/8/7 19:15
* version 1.0
* description 数据状态返回
**/
public class DataStateEnumHandler extends BaseTypeHandlerDataStateEnum {Overridepublic void setNonNullParameter(PreparedStatement ps, int i, DataStateEnum parameter, JdbcType jdbcType) throws SQLException {ps.setInt(i, parameter.getCode());}Overridepublic DataStateEnum getNullableResult(ResultSet rs, String columnName) throws SQLException {return getByCode(rs.getInt(columnName));}Overridepublic DataStateEnum getNullableResult(ResultSet rs, int columnIndex) throws SQLException {return getByCode(rs.getInt(columnIndex));}Overridepublic DataStateEnum getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {return getByCode(cs.getInt(columnIndex));}private DataStateEnum getByCode(Integer code) {DataStateEnum[] dataStateEnums DataStateEnum.values();for (DataStateEnum baseEnum : dataStateEnums) {if(Objects.equals(baseEnum.getCode(), code)) {return baseEnum;}}}
}这种方式很简单但是如果有多个枚举类会存在大量的重复代码所以我们可以把公用逻辑进行抽取其实只要让枚举有统一的类型并且获取到所有枚举就行了那么怎么做呢需要有以下的步骤 进阶方式 首先要提供一个接口然后所有枚举都实现这个接口如下
/**
* author zxc_user
* date 2023/8/7 19:01
* version 1.0
* description 枚举基础类
**/
public interface BaseEnumT{Integer getCode();String getDesc();
}/*** 数据状态*/
public enum DataStateEnum implements BaseEnumDataStateEnum{NORMAL(0, 正常),DELETE(1, 删除),;private final Integer code;private final String desc;DataStateEnum(Integer code, String desc) {this.code code;this.desc desc;}Overridepublic Integer getCode() {return code;}Overridepublic String getDesc() {return desc;}
}这样一来所有枚举都属于BaseEnum类型 其次提供了一个公用的TypeHandler处理器BaseEnumHandler定义如下
package com.zxc.movie.common.typehandler;import com.zxc.movie.common.enums.BaseEnum;
import com.zxc.movie.common.enums.BaseEnumUtils;
import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
/**
* author zxc_user
* date 2023/8/7 18:52
* version 1.0
* description 通用的枚举类解释器
**/
public abstract class BaseEnumHandlerT extends BaseEnumT extends BaseTypeHandlerT {//进一步优化protected abstract BaseEnumT[] getBaseEnumArray();//根据code获取对应的数据private BaseEnumT getBaseEnum(Integer code) {BaseEnumT[] baseEnumArray getBaseEnumArray();for (BaseEnumT baseEnum : baseEnumArray) {if(Objects.equals(baseEnum.getCode(), code)) {return baseEnum;}}return null;}Overridepublic void setNonNullParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException {ps.setInt(i, parameter.getCode());}Overridepublic T getNullableResult(ResultSet rs, String columnName) throws SQLException {return (T) getBaseEnum(rs.getInt(columnName));}Overridepublic T getNullableResult(ResultSet rs, int columnIndex) throws SQLException {return (T) getBaseEnum(rs.getInt(columnIndex));}Overridepublic T getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {return (T) getBaseEnum(cs.getInt(columnIndex));}
}
原来的DataStateEnumHandler只需要继承上面的处理器然后实现方法即可如下
package com.zxc.movie.common.typehandler.common;import com.zxc.movie.common.enums.BaseEnum;
import com.zxc.movie.common.enums.DataStateEnum;
import com.zxc.movie.common.typehandler.BaseEnumHandler;/**
* author zxc_user
* date 2023/8/7 19:15
* version 1.0
* description 数据状态返回
**/
public class DataStateEnumHandler extends BaseEnumHandlerDataStateEnum {Overrideprotected BaseEnumDataStateEnum[] getBaseEnumArray() {return DataStateEnum.values();}
}
是不是很简单到这里其实就已经很容易了但是其实还能进一步优化回看逻辑其实我们只要有办法拿到所有枚举的对象就可以处理那么有没有办法呢其实是有的可以通过反射如下
最终方式
package com.zxc.movie.common.typehandler;import com.zxc.movie.common.enums.BaseEnum;
import org.apache.ibatis.type.BaseTypeHandler;
import org.apache.ibatis.type.JdbcType;import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Objects;/**
* author zxc_user
* date 2023/8/7 18:52
* version 1.0
* description 通用的枚举类解释器
**/
public abstract class BaseEnumHandlerT extends BaseEnumT extends BaseTypeHandlerT {private BaseEnumT[] baseArrayEnum;public BaseEnumHandler(){//获取泛型的类型Type genericSuperclass this.getClass().getGenericSuperclass();if (genericSuperclass instanceof ParameterizedType){ParameterizedType parameterizedType (ParameterizedType) genericSuperclass;Type[] actualTypeArguments parameterizedType.getActualTypeArguments();for (Type actualTypeArgument : actualTypeArguments) {//获取枚举的所有对象因为都实现了BaseEnum接口this.baseArrayEnum (BaseEnum[]) ((Class)actualTypeArgument).getEnumConstants();}}}//根据code获取对应的数据private BaseEnumT getBaseEnum(Integer code) {for (BaseEnumT baseEnum : baseArrayEnum) {if(Objects.equals(baseEnum.getCode(), code)) {return baseEnum;}}return null;}Overridepublic void setNonNullParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException {ps.setInt(i, parameter.getCode());}Overridepublic T getNullableResult(ResultSet rs, String columnName) throws SQLException {return (T) getBaseEnum(rs.getInt(columnName));}Overridepublic T getNullableResult(ResultSet rs, int columnIndex) throws SQLException {return (T) getBaseEnum(rs.getInt(columnIndex));}Overridepublic T getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {return (T) getBaseEnum(cs.getInt(columnIndex));}
}最重要的地方就是构造器里面通过反射获取到枚举所有类型然后原来的处理器只需要直接继承就行了如下
package com.zxc.movie.common.typehandler.common;import com.zxc.movie.common.enums.DataStateEnum;
import com.zxc.movie.common.typehandler.BaseEnumHandler;/**
* author zxc_user
* date 2023/8/7 19:15
* version 1.0
* description 数据状态返回
**/
public class DataStateEnumHandler extends BaseEnumHandlerDataStateEnum {} 是不是变的很简单唯一的缺点就是还是需要创建一个转换器但是转换器已经不需要实现任何内容了只需要提供一个类就行了 TypeHandler生效 老版本的MyBatis是通过xml文件注册的这里就不说了因为现在都是需要和Spring进行集成的而且还是SpringBoot所以这里只说SpringBoot的方式 第一种 在application.yml文件中配置如下内容type-handlers-package为处理类所在包 mybatis-plus: type-handlers-package: com.zxc.movie.common.typehandler 第二种 往IOC容器中注入一个Bean,如下这是MyBatis-PLUS提供的扩展点是不是很方便 /**
* author zxc_user
* date 2023/8/7 19:17
* version 1.0
* description mybatis-plus配置类
**/
Configuration
public class MyBatisPlusConfig {/*** 自定义配置看源码发现的* return*/Beanpublic ConfigurationCustomizer mybatisConfiguration() {return configuration - {//注册解析器configuration.getTypeHandlerRegistry().register(DataStateEnumHandler.class);};}
} 这里顺便说一下第二种方式的优先度比第一种的要高这个逻辑需要在源码中查看或者官网介绍源码逻辑在MybatisPlusAutoConfiguration.applyConfiguration中有所体现 总结 到这里本篇文章就结束了其实并不复杂主要是为了统一TypeHandler的处理逻辑最妙的是通过反射获取的枚举列表方法如下,虽然不难不过也可以记录一下 public BaseEnumHandler(){//获取枚举类型Type genericSuperclass this.getClass().getGenericSuperclass();if (genericSuperclass instanceof ParameterizedType){ParameterizedType parameterizedType (ParameterizedType) genericSuperclass;Type[] actualTypeArguments parameterizedType.getActualTypeArguments();for (Type actualTypeArgument : actualTypeArguments) {this.baseArrayEnum (BaseEnum[]) ((Class)actualTypeArgument).getEnumConstants();}}}
