MyBatis 二级缓存

	<cache/>

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
		"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!-- 定义接口类 -->
<mapper namespace="com.ming.MyBatis.RoleMapper">
	
	<resultMap type="role" id="roleMap">
		<!-- id为主键映射关系 其中数据库中的id为主键 -->
		<id column="id" property="id" javaType="int" jdbcType="INTEGER"/>
		<!-- result为其他基本数据类型和实体类之间的映射 映射关系为role_name 到 roleName之间的映射 数据类型为string到VARCHAR之间的映射关系 -->
		<result column="role_name" property="roleName" javaType="string" jdbcType="VARCHAR"/>
		<!-- 这里使用typeHandler表示遇到此处理集的时候,将会执行com.ming.MyBatis.StringTypeHandler -->
		<result column="note" property="note" typeHandler="com.ming.MyBatis.StringTypeHandler"/>
	</resultMap>
	
	<select id="getRole" parameterType="int" resultType="com.ming.MyBatis.POJO.Role">
		SELECT id, role_name as roleName, note FROM t_role WHERE id = #{id}
	</select>
	
	<select id="findRoleByteMap" parameterType="map" resultMap="roleMap">
		SELECT id, role_name, note FROM t_role
		WHERE role_name LIKE CONCAT('%', #{roleName}, '%')
		AND note LIKE CONCAT('%', #{note}, '%')
	</select>
	
	<select id="findRoleByteMap1" resultMap="roleMap">
		SELECT id, role_name, note FROM t_role
		WHERE role_name LIKE CONCAT('%', #{roleName}, '%')
		AND note LIKE CONCAT('%', #{note}, '%')
	</select>
	
	
	<resultMap id="studentSelfCardMap" type="com.ming.MyBatis.POJO.StudentCard">
		<id column="uid" property="uid"/>
		<result column="student_number" property="studentNumber"/>
		<result column="birthplace" property="birthplace" />
		<result column="date_of_issue" property="dateOfIssue" jdbcType="DATE" javaType="java.util.Date"/>
		<result column="end_date" property="endDate" jdbcType="DATE" javaType="java.util.Date"/>
		<result column="remarks" property="remarks" />
	</resultMap>

	<select id="findStudentSelfCardByStudentId" parameterType="int" resultMap="studentSelfCardMap">
		SELECT student_card.uid, student_card.student_number, student_card.remarks,
		student_card.end_date, student_card.date_of_issue, student_card.birthplace
		FROM student_card WHERE student_card.uid = #{studentId};
	</select>
	
	<resultMap id="studentMap" type="com.ming.MyBatis.POJO.Student">
		<id column="uid" property="uid"/>
		<result column="student_name" property="studentName"/>
		<result column="gender" property="gender"/>
		<result column="student_id_number" property="studentIdNumber"/>
		<result column="remarks" property="remarks"/>
		<!--将会调用接口代表的SQL 进行执行查询 -->
		<association property="studentCard" column="uid" select="com.ming.MyBatis.RoleMapper.findStudentSelfCardByStudentId"/>
	</resultMap>
	
	<select id="getStudent" parameterType="int" resultMap="studentMap">
		SELECT student.uid, student.gender, student.remarks, student.student_id_number,
		student.student_name
		FROM student
		WHERE student.uid = 1;
	</select>
	
	<cache/>
</mapper>

	<cache eviction="LRU" flushInterval="100000" size="1024" readOnly="true"/>

Object object = new Object();

String str = new String("ming");      // 强引用
SoftReference<String> softRef = new SoftReference<String>(str);    // 软引用

String str = new String("ming");
WeakReference<String> weakReference = new WeakRefrence<String>(str);