前言
环境配置
什么是TypeHandler？
public interface TypeHandler<T> {
//设置参数，java类型转换为jdbc类型
void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException;
//将查询的结果转换为java类型
T getResult(ResultSet rs, String columnName) throws SQLException;
T getResult(ResultSet rs, int columnIndex) throws SQLException;
T getResult(CallableStatement cs, int columnIndex) throws SQLException;
}
如何自定义并使用TypeHandler？
如何自定义？
@MappedJdbcTypes(JdbcType.INTEGER)
@MappedTypes(String.class)
public class GenderTypeHandler extends BaseTypeHandler {
//设置参数，这里将Java的String类型转换为JDBC的Integer类型
@Override
public void setNonNullParameter(PreparedStatement ps, int i, Object parameter, JdbcType jdbcType) throws SQLException {
ps.setInt(i, StringUtils.equals(parameter.toString(),"男")?1:2);
}
//以下三个参数都是将查询的结果转换
@Override
public Object getNullableResult(ResultSet rs, String columnName) throws SQLException {
return rs.getInt(columnName)==1?"男":"女";
}
@Override
public Object getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
return rs.getInt(columnIndex)==1?"男":"女";
}
@Override
public Object getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
return cs.getInt(columnIndex)==1?"男":"女";
}
}
如何将其添加到Mybatis中？
## 设置自定义的Typehandler所在的包，启动的时候会自动扫描配置到Mybatis中
mybatis.type-handlers-package=cn.cb.demo.typehandler
@Bean("sqlSessionFactory")
public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
sqlSessionFactoryBean.setDataSource(dataSource);
sqlSessionFactoryBean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources(MAPPER_LOCATOIN));
org.apache.ibatis.session.Configuration configuration = new org.apache.ibatis.session.Configuration();
// 自动将数据库中的下划线转换为驼峰格式
configuration.setMapUnderscoreToCamelCase(true);
configuration.setDefaultFetchSize(100);
configuration.setDefaultStatementTimeout(30);
sqlSessionFactoryBean.setConfiguration(configuration);
//将typehandler注册到mybatis
GenderTypeHandler genderTypeHandler = new GenderTypeHandler();
TypeHandler[] typeHandlers=new TypeHandler[]{genderTypeHandler};
sqlSessionFactoryBean.setTypeHandlers(typeHandlers);
return sqlSessionFactoryBean.getObject();
}
XML文件中如何指定TypeHandler？
<insert id="insertUser">
insert into user_info(user_id,his_id,name,gender,password,create_time)
values(#{userId,jdbcType=VARCHAR},#{hisId,jdbcType=VARCHAR},#{name,jdbcType=VARCHAR},
#{gender,jdbcType=INTEGER,typeHandler=cn.cb.demo.typehandler.GenderTypeHandler},#{password,jdbcType=VARCHAR},now())
</insert>
<resultMap id="userResultMap" type="cn.cb.demo.domain.UserInfo">
<id column="id" property="id"/>
<result column="user_id" property="userId"/>
<result column="his_id" property="hisId"/>
<!-- 指定typeHandler属性为全类名-->
<result column="gender" property="gender" typeHandler="cn.cb.demo.typehandler.GenderTypeHandler"/>
<result column="name" property="name"/>
<result column="password" property="password"/>
</resultMap>
<select id="selectList" resultMap="userResultMap">
select * from user_info where status=1
and user_id in
<foreach collection="userIds" item="item" open="(" separator="," close=")" >
#{item}
</foreach>
</select>
源码中如何执行TypeHandler？
入参如何转换？
@Override
public void parameterize(Statement statement) throws SQLException {
//实际调用的是DefaultParameterHandler
parameterHandler.setParameters((PreparedStatement) statement);
}
public void setParameters(PreparedStatement ps) {
ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());
//获取参数映射
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
//遍历参数映射，一一设置
if (parameterMappings != null) {
for (int i = 0; i < parameterMappings.size(); i++) {
ParameterMapping parameterMapping = parameterMappings.get(i);
if (parameterMapping.getMode() != ParameterMode.OUT) {
Object value;
String propertyName = parameterMapping.getProperty();
if (boundSql.hasAdditionalParameter(propertyName)) { // issue #448 ask first for additional params
value = boundSql.getAdditionalParameter(propertyName);
} else if (parameterObject == null) {
value = null;
} else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
value = parameterObject;
} else {
MetaObject metaObject = configuration.newMetaObject(parameterObject);
value = metaObject.getValue(propertyName);
}
//获取类型处理器，如果不存在，使用默认的
TypeHandler typeHandler = parameterMapping.getTypeHandler();
//JdbcType
JdbcType jdbcType = parameterMapping.getJdbcType();
if (value == null && jdbcType == null) {
jdbcType = configuration.getJdbcTypeForNull();
}
try {
//调用类型处理器中的方法设置参数，将Java类型转换为JDBC类型
typeHandler.setParameter(ps, i + 1, value, jdbcType);
} catch (TypeException e) {
throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
} catch (SQLException e) {
throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
}
}
}
}
}
结果如何转换？
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
PreparedStatement ps = (PreparedStatement) statement;
//执行SQL
ps.execute();
//处理结果
return resultSetHandler.handleResultSets(ps);
}
private Object getPropertyMappingValue(ResultSet rs, MetaObject metaResultObject, ResultMapping propertyMapping, ResultLoaderMap lazyLoader, String columnPrefix)
throws SQLException {
if (propertyMapping.getNestedQueryId() != null) {
return getNestedQueryMappingValue(rs, metaResultObject, propertyMapping, lazyLoader, columnPrefix);
} else if (propertyMapping.getResultSet() != null) {
addPendingChildRelation(rs, metaResultObject, propertyMapping); // TODO is that OK?
return DEFERRED;
} else {
final TypeHandler<?> typeHandler = propertyMapping.getTypeHandler();
final String column = prependPrefix(propertyMapping.getColumn(), columnPrefix);
//执行typeHandler中的方法获取结果并且转换为对应的Java类型
return typeHandler.getResult(rs, column);
}
}
总结
总结