XML映射配置文件

1. http://www.mybatis.org/mybatis-3/configuration.html

2. Type Handlers 类型处理器

每当MyBatis在PreparedStatement上设置参数或从ResultSet中检索值时，都会使用TypeHandler以适合Java类型的方式检索值。下表描述了默认的TypeHandlers。
注意 从版本3.4.5开始，MyBatis默认支持JSR-310（日期和时间API）

• 可以 override 原有的 handlers

• 可以创造自己的 handler 补充没实现的类

• 实例：

    import org.apache.ibatis.type.BaseTypeHandler;
    import org.apache.ibatis.type.JdbcType;
    import org.apache.ibatis.type.MappedJdbcTypes;
    import org.apache.ibatis.type.MappedTypes;
    
    import java.sql.CallableStatement;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    import java.util.Date;
    
    /**
     * 日期转换
     * 数据库是varchar,java类型是Date
     */
    @MappedJdbcTypes(JdbcType.VARCHAR)
    @MappedTypes(Date.class)
    public class TestTypeHandler extends BaseTypeHandler<Date> {
    
        public void setNonNullParameter(PreparedStatement ps, int i, Date parameter, JdbcType jdbcType) throws SQLException {
            ps.setString(i,String.valueOf(parameter.getTime()));
        }
    
        public Date getNullableResult(ResultSet rs, String columnName) throws SQLException {
            return new Date(rs.getLong(columnName));
        }
    
        public Date getNullableResult(ResultSet rs, int columnIndex) throws SQLException {
            return new Date(rs.getLong(columnIndex));
        }
    
        public Date getNullableResult(CallableStatement cs, int columnIndex) throws SQLException {
            return cs.getDate(columnIndex);
        }
    }

    <!--配置方式一-->
    <!--当我们进行数据库的读取操作的时候，秒数就会自动转为Date对象-->
    <resultMap id="testResultMap" type="Test">
        <result typeHandler="typehandlers.TestTypeHandler" column="reg" javaType="java.util.Date"
                jdbcType="VARCHAR" property="reg"/>
    </resultMap>
    <insert id="insertExample" parameterType="Test">
        insert into test(reg) values (#{reg,typeHandler=typehandlers.TestTypeHandler})
    </insert>

    <!--配置方式二 在config中配置-->
    <!--当我们进行数据库的读取操作的时候，秒数就会自动转为Date对象-->
    <typeHandlers>
        <typeHandler handler="typehandlers.TestTypeHandler"/>
    </typeHandlers>

1. plugins

        import org.apache.ibatis.executor.Executor;
        import org.apache.ibatis.mapping.BoundSql;
        import org.apache.ibatis.mapping.MappedStatement;
        import org.apache.ibatis.plugin.*;
        import org.apache.ibatis.session.ResultHandler;
        import org.apache.ibatis.session.RowBounds;
        
        import java.util.Properties;
        
        /**
         * 在映射语句的执行中拦截对某些点的调用
         * Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed)
         * ParameterHandler (getParameterObject, setParameters)
         * ResultSetHandler (handleResultSets, handleOutputParameters)
         * StatementHandler (prepare, parameterize, batch, update, query)
         */
        @Intercepts(@Signature(type = Executor.class,
                method = "query",
                args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class}
        ))
        public class TestPlugin implements Interceptor {
            public Object intercept(Invocation invocation) throws Throwable {
                MappedStatement mappedStatement = (MappedStatement) invocation.getArgs()[0];
                BoundSql boundSql = mappedStatement.getBoundSql(invocation.getArgs()[1]);
                System.out.println(String.format("sql语句:%s,返回值:%s",boundSql.getSql(),boundSql.getParameterObject()));
                return invocation.proceed();
            }
        
            public Object plugin(Object target) {
                return Plugin.wrap(target,this);
            }
        
            public void setProperties(Properties properties) {
        
            }
        }

    <plugins>
        <plugin interceptor="plugins.TestPlugin"></plugin>
    </plugins>

占位符中指定默认值

    <!--占位符中指定默认值，启用此功能-->
    <!--
    文档:
    http://www.mybatis.org/mybatis-3/configuration.html-->
    <properties resource="db.properties">
        <property name="org.apache.ibatis.parsing.PropertyParser.enable-default-value" value="true"/>
    </properties>

    <!--MyBatis 3.4.2开始，您可以在占位符中指定默认值-->
    <dataSource type="POOLED">
        <property name="driver" value="${db.driver}"/>
        <property name="url" value="${db.url}"/>
        <property name="username" value="${db.username:root}"/>
        <property name="password" value="${db.password:root}"/>
    </dataSource>