Mybatis3 快速入门
Mybatis3 快速入门
目前常见的持久层java框架有Hibernate,Mybatis,SpringData。笔者比较喜欢用SpringData。Hibernate 和 Mybatis 也经常用。今天通过 Mybatis 的简介,数据的增删改查,表的级联查询,动态SQL语句 来快速入门 Mybatis 。
1 Mybatis 简介
摘录百度百科的内容:MyBatis 是一款优秀的持久层框架,它支持定制化 SQL、存储过程以及高级映射。MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集。MyBatis 可以使用简单的 XML 或注解来配置和映射原生信息,将接口和 Java 的 POJOs(Plain Old Java Objects,普通的 Java对象)映射成数据库中的记录
如果 Hibernate 是自动化持久层框架,那么 Mybatis 就是半自动化持久层框架。 半自动 ??? 听起来好像 lower 了。其实不然,Mybatis 将 sql 和 java 分离开。让专业的db工程师负责 sql 的优化,提高其性能,在高并发的场景,系统依然 稳如dog 。程序员可以把更多的精力放在业务逻辑上。
Mybatis:https://github.com/mybatis/mybatis-3/
2 Mybatis 快速入门
需求:使用 mybatis 框架完成数据的增删改查操作,和级联查询,模糊查询,调用存储过程,使用mybatis的一二级缓存
技术:mybatis,maven
源码:见文章底部
说明:本文内容属于快速入门,通过手写 xml 映射文件了解 mybatis 的工作原理。实际开发中,一般采用官方提供的逆向工程自动生成需要的 java 文件和 xml 文件
结构:
准备:
Mysql数据库表结构
创建四张表,其中 person 独立存在。classroom 和 student,teacher 存在主外键关系。
① classroom 的 student_id 和 student 的 class_id 存在主外键关系,并且是一对多的关系
② classroom 的 teacher_id 和 teacher 的 id 存在主外键关系,并且是一对一的关系
SET FOREIGN_KEY_CHECKS=0; -- ---------------------------- -- Table structure for classroom -- ---------------------------- DROP TABLE IF EXISTS `classroom`; CREATE TABLE `classroom` ( `id` int(11) NOT NULL AUTO_INCREMENT, `room` varchar(255) DEFAULT NULL, `teacher_id` int(11) DEFAULT NULL, `student_id` int(11) DEFAULT NULL, PRIMARY KEY (`id`), KEY `c_t_id` (`teacher_id`), KEY `c_s_id` (`student_id`), CONSTRAINT `c_t_id` FOREIGN KEY (`teacher_id`) REFERENCES `teacher` (`id`) ON DELETE SET NULL ON UPDATE CASCADE ) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8; -- ---------------------------- -- Records of classroom -- ---------------------------- INSERT INTO `classroom` VALUES ('1', 'JavaEE', '1', '1'); INSERT INTO `classroom` VALUES ('2', 'Linux', '2', '2'); -- ---------------------------- -- Table structure for person -- ---------------------------- DROP TABLE IF EXISTS `person`; CREATE TABLE `person` ( `id` int(11) NOT NULL AUTO_INCREMENT, `email` varchar(255) DEFAULT NULL, `last_name` varchar(255) DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8; -- ---------------------------- -- Records of person -- ---------------------------- INSERT INTO `person` VALUES ('1', 'lxl@qq.com', 'lxl'); INSERT INTO `person` VALUES ('2', 'cyy@qq.com', 'cyy'); INSERT INTO `person` VALUES ('3', 'itdrgon@qq.com', 'itdragon'); INSERT INTO `person` VALUES ('4', 'java@qq.com', 'java'); -- ---------------------------- -- Table structure for student -- ---------------------------- DROP TABLE IF EXISTS `student`; CREATE TABLE `student` ( `id` int(11) NOT NULL AUTO_INCREMENT, `name` varchar(255) DEFAULT NULL, `class_id` int(11) DEFAULT NULL, PRIMARY KEY (`id`), KEY `s_c_id` (`class_id`), CONSTRAINT `s_c_id` FOREIGN KEY (`class_id`) REFERENCES `classroom` (`student_id`) ON DELETE SET NULL ON UPDATE CASCADE ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8; -- ---------------------------- -- Records of student -- ---------------------------- INSERT INTO `student` VALUES ('1', 'ITDragon', '1'); INSERT INTO `student` VALUES ('2', 'Marry', '1'); INSERT INTO `student` VALUES ('3', 'XiaoMing', '2'); -- ---------------------------- -- Table structure for teacher -- ---------------------------- DROP TABLE IF EXISTS `teacher`; CREATE TABLE `teacher` ( `id` int(11) NOT NULL AUTO_INCREMENT, `subject` varchar(255) DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8; -- ---------------------------- -- Records of teacher -- ---------------------------- INSERT INTO `teacher` VALUES ('1', 'Java'); INSERT INTO `teacher` VALUES ('2', 'Docker');
Maven 项目的核心文件 pom.xml (有些不是必要的,后续做整合会用到)
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.itdragon.mybatis</groupId> <artifactId>mybatis-basic</artifactId> <version>0.0.1-SNAPSHOT</version> <properties> <commons-lang3.version>3.3.2</commons-lang3.version> <commons-io.version>1.3.2</commons-io.version> <commons-net.version>3.3</commons-net.version> <junit.version>4.12</junit.version> <slf4j.version>1.6.4</slf4j.version> <mybatis.version>3.2.8</mybatis.version> <mybatis.spring.version>1.2.2</mybatis.spring.version> <mybatis.paginator.version>1.2.15</mybatis.paginator.version> <mysql.version>5.1.6</mysql.version> <druid.version>1.0.9</druid.version> </properties> <dependencies> <!-- Apache工具组件 --> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-lang3</artifactId> <version>${commons-lang3.version}</version> </dependency> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-io</artifactId> <version>${commons-io.version}</version> </dependency> <dependency> <groupId>commons-net</groupId> <artifactId>commons-net</artifactId> <version>${commons-net.version}</version> </dependency> <!-- 单元测试 --> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>${junit.version}</version> <scope>test</scope> </dependency> <!-- 日志处理 --> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-log4j12</artifactId> <version>${slf4j.version}</version> </dependency> <!-- Mybatis --> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>${mybatis.version}</version> </dependency> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis-spring</artifactId> <version>${mybatis.spring.version}</version> </dependency> <dependency> <groupId>com.github.miemiedev</groupId> <artifactId>mybatis-paginator</artifactId> <version>${mybatis.paginator.version}</version> </dependency> <!-- MySql --> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>${mysql.version}</version> </dependency> <!-- 连接池 --> <dependency> <groupId>com.alibaba</groupId> <artifactId>druid</artifactId> <version>${druid.version}</version> </dependency> </dependencies> </project>
Mybatis 的配置文件 SqlMapConfig.xml
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <!-- 标签必须按顺序写,否则会提示错误:The content of element type "configuration" must match "(properties?,settings?,...)". --> <!-- 引入配置文件 --> <properties resource="db.properties" /> <!-- 配置实体类的别名 --> <typeAliases> <!-- 给指定包取别名,别名为实体类对应的简单类名,如 com.itdragon.pojo.Person 的别名就是 Person --> <package name="com.itdragon.pojo" /> </typeAliases> <!-- 配置数据库链接 --> <environments default="development"> <environment id="development"> <transactionManager type="JDBC" /> <dataSource type="POOLED"> <property name="driver" value="${jdbc.driver}" /> <property name="url" value="${jdbc.url}" /> <property name="username" value="${jdbc.username}" /> <property name="password" value="${jdbc.password}" /> </dataSource> </environment> </environments> <!-- 注册映射文件 --> <mappers> <mapper resource="com/itdragon/mapper/PersonMapper.xml" /> <mapper resource="com/itdragon/mapper/ClassroomMapper.xml" /> </mappers> </configuration>
数据库的配置文件 db.properties
jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/jpa?characterEncoding=utf-8
jdbc.username=root
jdbc.password=root
到这里准备工作就做完了。
3 数据的增删改查
Person.java 实体类
package com.itdragon.pojo; // 学习 mybatis crud 实体类 public class Person { private Integer id; private String email; private String lastName; // 这里lastName 在数据库中对应的是 last_name, 这会出现:字段名与实体类属性名不相同的冲突问题 public Person() { } public Person(Integer id, String email, String lastName) { this.id = id; this.email = email; this.lastName = lastName; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email == null ? null : email.trim(); } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName == null ? null : lastName.trim(); } @Override public String toString() { return "Person [id=" + id + ", email=" + email + ", lastName=" + lastName + "]"; } }
PersonMapper.xml 查询数据的映射文件
<?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"> <mapper namespace="com.itdragon.mapper.PersonMapper"> <!-- CRUD 操作 --> <!-- 基础知识: select 查询数据 insert 插入数据 delete 删除数据 update 更新数据 namespace 命名空间 id 方法名, 命名空间 + 方法名 = 唯一方法 parameterType 传入参数类型 resultType 返回值类型 resultMap 以键值对的类型返回结果 参数传值:#{xxx} parameterType 如果不是实体类,对应的参数名可以自定义。如 #{id} 也可以是 #{xxxx} 如果是实体类,对应的参数名必须是实体类属性名。为了避免错误,尽量全部都用属性名。 扩展知识: resultType 的值是 com.itdragon.pojo.Person 全类名,但为了方便,可以考虑使用别名 resultMap 为了避免类似 lastName 和 last_name 冲突,导致查询的 last_name 会是 null 问题,可以设置键值关系 --> <select id="getPersonById" parameterType="int" resultType="com.itdragon.pojo.Person"> select * from person where id=#{id} </select> <!-- 解决字段名与实体类属性名不相同的冲突问题第一种办法(不推荐) --> <select id="getPersonByIdOne" parameterType="int" resultType="com.itdragon.pojo.Person"> select id, email, last_name lastName from person where id=#{id} </select> <select id="getPersonByIdTwo" parameterType="int" resultMap="getPersonMap"> select * from person where id=#{id} </select> <!-- 使用 resultMap 设置冲突字段名和实体类属性名对应关系,(推荐) --> <resultMap type="Person" id="getPersonMap"> <result property="lastName" column="last_name" /> </resultMap> <!-- parameterType 中直接使用了 Person 是因为在 SqlMapConfig.xml 文件中设置了别名 --> <insert id="createPerson" parameterType="Person"> insert into person(email, last_name) values(#{email}, #{lastName}) </insert> <delete id="deletePersonById" parameterType="int"> delete from person where id=#{id} </delete> <update id="updatePersonById" parameterType="Person"> update person set email=#{email}, last_name=#{lastName} where id=#{id} </update> <select id="getAllperson" resultType="Person"> select * from person </select> </mapper>
测试方法:
package com.itdragon.test; import java.io.InputStream; import java.util.HashMap; import java.util.List; import java.util.Map; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; import org.junit.Test; import com.itdragon.pojo.Classroom; import com.itdragon.pojo.Person; public class MyBatisTest { public SqlSession getSqlSession() { String resource = "SqlMapConfig.xml"; InputStream is = MyBatisTest.class.getClassLoader().getResourceAsStream(resource); SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(is); SqlSession session = factory.openSession(true); // false 默认手动提交, true 自动提交 return session; } // crud 操作 @Test public void getPersonById() { String statement = "com.itdragon.mapper.PersonMapper.getPersonById"; Person person = getSqlSession().selectOne(statement, 2); System.out.println(person); statement = "com.itdragon.mapper.PersonMapper.getPersonByIdOne"; person = getSqlSession().selectOne(statement, 2); System.out.println(person); statement = "com.itdragon.mapper.PersonMapper.getPersonByIdTwo"; person = getSqlSession().selectOne(statement, 2); System.out.println(person); } @Test public void getAllperson() { String statement = "com.itdragon.mapper.PersonMapper.getAllperson"; List<Person> persons = getSqlSession().selectList(statement); System.out.println(persons); } @Test public void createPerson() { String statement = "com.itdragon.mapper.PersonMapper.createPerson"; int result = getSqlSession().insert(statement, new Person(3, "itdragon@qq.com", "ITDragon")); System.out.println(result); } @Test public void updatePersonById() { String statement = "com.itdragon.mapper.PersonMapper.updatePersonById"; int result = getSqlSession().update(statement, new Person(4, "itdragon@qq.com", "ITDragon博客")); System.out.println(result); } @Test public void deletePersonById() { String statement = "com.itdragon.mapper.PersonMapper.deletePersonById"; int result = getSqlSession().delete(statement, 4); System.out.println(result); } }
4 级联查询
为了满足一对一和一对多的级联操作,新增三个实体类,分别是 Classroom(教室),Teacher(老师),Student(学生)
Classroom 和 Teacher 是一对一的关系,Classroom 和 Student 是一对多的关系
package com.itdragon.pojo; import java.io.Serializable; import java.util.List; // 学习 表的关联关系所用字段,一个教室关联一个老师(一对一),一个教室关联一群学生(一对多) public class Classroom implements Serializable { private Integer id; private String room; private Teacher teacher; private List<Student> students; public Classroom() { } public Classroom(Integer id, String room, Teacher teacher, List<Student> students) { this.id = id; this.room = room; this.teacher = teacher; this.students = students; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getRoom() { return room; } public void setRoom(String room) { this.room = room; } public Teacher getTeacher() { return teacher; } public void setTeacher(Teacher teacher) { this.teacher = teacher; } public List<Student> getStudents() { return students; } public void setStudents(List<Student> students) { this.students = students; } @Override public String toString() { return "Classroom [id=" + id + ", room=" + room + ", teacher=" + teacher + ", students=" + students + "]"; } }
package com.itdragon.pojo; import java.io.Serializable; public class Teacher implements Serializable{ private Integer id; private String subject; public Teacher() { } public Teacher(Integer id, String subject) { this.id = id; this.subject = subject; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getSubject() { return subject; } public void setSubject(String subject) { this.subject = subject; } @Override public String toString() { return "Teacher [id=" + id + ", subject=" + subject + "]"; } }
package com.itdragon.pojo; import java.io.Serializable; public class Student implements Serializable { private Integer id; private String name; public Student() { } public Student(Integer id, String name) { this.id = id; this.name = name; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Override public String toString() { return "Student [id=" + id + ", name=" + name + "]"; } }
ClassroomMapper.xml
<?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"> <mapper namespace="com.itdragon.mapper.ClassroomMapper"> <!-- 关联表查询 --> <!-- 基础知识: association:用于一对一的关联查询 property:对象的属性名 javaType:对象的类型 column:对应数据表中外键 select:使用另外一个查询的封装结果 collection:用于一对多的关联查询 ofType:指定集合对象的类型 --> <!-- 需求:通过 id 查询 classroom, 并打印 teacher 信息 嵌套查询:通过执行另外一个SQL映射语句来返回预期的复杂类型 第一步:先查询 classroom SELECT * FROM classroom WHERE id=?; 第二步:再查询 teacher SELECT * FROM teacher WHERE id=classroom.id //classroom 是第一步的查询结果 说明:嵌套查询的方法,虽然好理解,当时不建议 --> <select id="getClassroomById" parameterType="int" resultMap="getClassroomMap"> SELECT * FROM classroom WHERE id=#{id} </select> <select id="getTeacherById" parameterType="int" resultType="Teacher"> SELECT * FROM teacher WHERE id=#{id} </select> <resultMap type="Classroom" id="getClassroomMap"> <association property="teacher" column="teacher_id" select="getTeacherById"> <!-- 如果 teacher 存在属性字段和字段冲突,需要在这里设置 --> </association> </resultMap> <!-- 需求:通过 id 查询 classroom, 并打印 teacher 信息 嵌套结果:使用嵌套结果映射来处理重复的联合结果的子集,封装联表查询的数据(去除重复的数据) select * from classroom, teacher where classroom.teacher_id=teacher.id and classroom.id=? --> <select id="getClassroom2ById" parameterType="int" resultMap="getClassroom2Map"> SELECT * FROM classroom c, teacher WHERE c.teacher_id = teacher.id AND c.id = #{id} </select> <resultMap type="Classroom" id="getClassroom2Map"> <id property="id" column="id"/> <result property="room" column="room"/> <association property="teacher" javaType="Teacher"> <id property="id" column="id"/> <result property="subject" column="subject"/> </association> </resultMap> <!-- 需求:通过 id 查询 classroom, 并打印 teacher 和 student 信息 嵌套查询:通过执行另外一个SQL映射语句来返回预期的复杂类型 第一步:先查询 classroom SELECT * FROM classroom WHERE id=?; 第二步:再查询 teacher SELECT * FROM teacher WHERE id=classroom.id //classroom 是第一步的查询结果 第三步:再查询 student SELECT * FROM student WHERE id=classroom.id //classroom 是第一步的查询结果 --> <select id="getClassroom3ById" resultMap="getClassroom3Map"> SELECT * FROM classroom WHERE id=#{id} </select> <!-- getTeacherById 上面有了,就不重复写了 --> <select id="getStudentById" parameterType="int" resultType="Student"> SELECT * FROM student WHERE class_id=#{id} </select> <resultMap type="Classroom" id="getClassroom3Map"> <association property="teacher" column="teacher_id" select="getTeacherById"></association> <collection property="students" column="student_id" select="getStudentById"></collection> </resultMap> <!-- 需求:通过 id 查询 classroom, 并打印 teacher 和 student 信息 嵌套结果:使用嵌套结果映射来处理重复的联合结果的子集,封装联表查询的数据(去除重复的数据) SELECT * FROM classroom c, teacher t,student s WHERE c.teacher_id=t.id AND c.id=s.class_id AND c.id=? --> <select id="getClassroom4ById" parameterType="int" resultMap="getClassroom4Map"> SELECT * FROM classroom c, teacher t, student s WHERE c.teacher_id=t.id AND c.student_id=s.class_id AND c.id=#{id} </select> <resultMap type="Classroom" id="getClassroom4Map"> <id property="id" column="id"/> <result property="room" column="room"/> <association property="teacher" javaType="Teacher"> <id property="id" column="id"/> <result property="subject" column="subject"/> </association> <collection property="students" ofType="Student"> <!-- 存在问题 如果两表联查,主表和明细表的主键都是id的话,明细表的多条只能查询出来第一条。 <id property="id" column="s_id"/> 解决方法:https://www.cnblogs.com/junge/p/5145881.html --> <result property="name" column="name"/> </collection> </resultMap> </mapper>
测试方法:
// 关联表的查询 @Test public void getClassroomById() { String statement = "com.itdragon.mapper.ClassroomMapper.getClassroomById"; Classroom classroom = getSqlSession().selectOne(statement, 1); System.out.println(classroom); statement = "com.itdragon.mapper.ClassroomMapper.getClassroom2ById"; classroom = getSqlSession().selectOne(statement, 1); System.out.println(classroom); statement = "com.itdragon.mapper.ClassroomMapper.getClassroom3ById"; classroom = getSqlSession().selectOne(statement, 1); System.out.println(classroom); statement = "com.itdragon.mapper.ClassroomMapper.getClassroom4ById"; classroom = getSqlSession().selectOne(statement, 1); System.out.println(classroom); }
5 动态SQL语句
这里通过模糊查询 Email 来了解动态SQL语句,在 PersonMapper.xml 中添加如下代码
<!-- 动态SQL与模糊查询 --> <!-- 需求:通过模糊查询邮箱和指定id范围查询数据 动态SQL: if:判断语句 <if test=''></if> where:去掉多余的 and 和 or <where><if test=''>AND xxx</if></where> set:去掉多余的 "," <set><if test=''>xxx , </if></set> trim: 代替 where , set if + where == <trim prefix="WHERE" prefixOverrides="AND |OR "></trim> if + set == <trim prefix="SET" suffixOverrides=","></trim> choose: (when, otherwise) 类似java的switch case default <choose><when test="">xxx</when><otherwise>xxx</otherwise></choose> foreach:类似java的加强for循环 <foreach collection="array" item="xxx" open="(" separator="," close=")"></foreach> 说明:mybatis 提供了自动生成的逆向工程的工具,这里只需要了解即可,虽然是很重要的知识点 学习博客:http://limingnihao.iteye.com/blog/782190 --> <select id="getPersonLikeKey" parameterType="Person" resultMap="getPersonMap"> select * from person where <if test='email != "%null%"'> email like #{email} and </if> id > #{id} </select>
测试方法:
// 调用存储过程 @Test public void getPersonCountGtId(){ String statement = "com.itdragon.mapper.PersonMapper.getPersonCountGtId"; Map<String, Integer> parameterMap = new HashMap<String, Integer>(); parameterMap.put("personId", 1); parameterMap.put("personCount", -1); getSqlSession().selectOne(statement, parameterMap); Integer result = parameterMap.get("personCount"); System.out.println(result); }
6 存储过程
引用百度百科:存储过程(Stored Procedure)是在大型数据库系统中,一组为了完成特定功能的SQL 语句集,存储在数据库中,经过第一次编译后再次调用不需要再次编译,用户通过指定存储过程的名字并给出参数(如果该存储过程带有参数)来执行它。存储过程是数据库中的一个重要对象。
这里通过获取大于Person id 数量的逻辑来了解Mybatis 是如何调用存储过程的。首先在Mysql 命令行中执行一下代码
#创建存储过程 传入Id的值,返回id大于该值的数量 DELIMITER $ #在 jpa 数据库中,创建一个名为get_person_count的方法,传入参数是person_id,返回参数是person_count CREATE PROCEDURE jpa.get_person_count(IN person_id INT, OUT person_count INT) BEGIN SELECT COUNT(*) FROM jpa.person WHERE person.id > person_id INTO person_count; END $ #调用存储过程 DELIMITER ; SET @person_count = 0; CALL jpa.get_person_count(1, @person_count); SELECT @person_count;
打印结果如下,则说明创建成功了
还是在 PersonMapper.xml 文件中添加如下代码
<!-- 调用存储过程 --> <!-- 通过id,获取大于该id的数量 CALL jpa.get_person_count(1, @person_count); 注意:需关闭二级缓存 Caching stored procedures with OUT params is not supported. Please configure useCache=false in ... --> <select id="getPersonCountGtId" parameterMap="getPersonCountMap" statementType="CALLABLE"> CALL jpa.get_person_count(?,?) </select> <parameterMap type="java.util.Map" id="getPersonCountMap"> <parameter property="personId" mode="IN" jdbcType="INTEGER"/> <parameter property="personCount" mode="OUT" jdbcType="INTEGER"/> </parameterMap>
测试方法:
// 调用存储过程 @Test public void getPersonCountGtId(){ String statement = "com.itdragon.mapper.PersonMapper.getPersonCountGtId"; Map<String, Integer> parameterMap = new HashMap<String, Integer>(); parameterMap.put("personId", 1); parameterMap.put("personCount", -1); getSqlSession().selectOne(statement, parameterMap); Integer result = parameterMap.get("personCount"); System.out.println(result); }
7 一二级缓存
一级缓存:基于PerpetualCache 的 HashMap本地缓存,其存储作用域为 Session,当 Session flush 或 close 之后,该Session中的所有 Cache 就将清空。
① 若Session 被关闭了,缓存清空
② 若数据执行了 创建,更新,删除操作,缓存清空
③ 如果不是同一个Session,缓存失效
二级缓存:与一级缓存其机制相同,不同在于其存储作用域为 Mapper(Namespace),并且可自定义存储源,如 Ehcache。
① 默认是关闭的
② 是一个映射文件级的缓存,
③ 开启二级缓存 <cache/>
还是在 PersonMapper.xml 文件中添加如下代码
<!-- 开启二级缓存 --> <!-- eviction="FIFO" 回收策略为先进先出 flushInterval="60000" 自动刷新时间60s size="512" 最多缓存512个引用对象 readOnly="true" 只读 --> <cache eviction="FIFO" flushInterval="60000" size="1024" readOnly="true"/>
打印结果如下
log4j:WARN No appenders could be found for logger (org.apache.ibatis.logging.LogFactory). log4j:WARN Please initialize the log4j system properly. log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info. [Person [id=2, email=cyy@qq.com, lastName=cyy]] 1 0 Classroom [id=1, room=JavaEE, teacher=Teacher [id=1, subject=Java], students=null] Classroom [id=1, room=JavaEE, teacher=Teacher [id=1, subject=Java], students=null] Classroom [id=1, room=JavaEE, teacher=Teacher [id=1, subject=Java], students=[Student [id=1, name=ITDragon], Student [id=2, name=Marry]]] Classroom [id=1, room=JavaEE, teacher=Teacher [id=1, subject=Java], students=[Student [id=null, name=ITDragon], Student [id=null, name=Marry]]] [Person [id=1, email=lxl@qq.com, lastName=null], Person [id=2, email=cyy@qq.com, lastName=null], Person [id=3, email=itdrgon@qq.com, lastName=null]] Person [id=2, email=cyy@qq.com, lastName=null] Person [id=2, email=cyy@qq.com, lastName=cyy] Person [id=2, email=cyy@qq.com, lastName=cyy] 2 1
源码地址:https://github.com/ITDragonBlog/daydayup/tree/master/mybatis/mybatis-basic
到这里,Mybatis 的入门知识就讲完了。如果大家觉得不错,可以关注我!后续还有很多不错的内容提供。
出处:http://www.cnblogs.com/itdragon/
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