XML映射配置文件

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

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>