mybatis学习 (二) SqlSessionFactory单例创建

男娘i 2022-05-28 23:21 228阅读 0赞

SqlSessionFactory是创建SqlSession的工厂，但是创建过程中需要反复加载全局配置文件，这一点是十分耗时的，我们希望SqlSessionFactory对于一个数据库而言只有一个实例。单例模式的好处是可以重复的使用这个唯一的对象

## 创建方式 ##

对构造函数进行私有化  
对类加锁， 防止多线程环境造成对象不唯一

代码如下， openSqlSession返回一个SqlSession

public class SqlSessionFactoryUtil { 
        private static SqlSessionFactory sqlSessionFactory;
        private static final Class CLASS_LOCK = SqlSessionFactoryUtil.class;
    
        /** * 私有化构造 */
        private SqlSessionFactoryUtil(){
        }
        /* * 单实例对象 */
        public static SqlSessionFactory initSqlSessionFactory(){
            String resource = "mybatis-config.xml";
            InputStream inputStream = null;
            try {
                inputStream = Resources.getResourceAsStream(resource);
            }catch (IOException e){
                e.printStackTrace();
            }
            synchronized (CLASS_LOCK){
                if(sqlSessionFactory == null){
                    sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
                }
            }
            return sqlSessionFactory;
        }
    
        public static SqlSession openSqlSession(){
            if (sqlSessionFactory == null){
                initSqlSessionFactory();
            }
            return sqlSessionFactory.openSession();
        }
    
    }

### pojo类 ###

public class Student {
    
        private Integer stuId;
        private String stuName;
        private Integer stuAge;
        private String stuMajor;
    
        public Integer getStuId() {
            return stuId;
        }
    
        public void setStuId(Integer stuId) {
            this.stuId = stuId;
        }
    
        public String getStuName() {
            return stuName;
        }
    
        public void setStuName(String stuName) {
            this.stuName = stuName;
        }
    
        public Integer getStuAge() {
            return stuAge;
        }
    
        public void setStuAge(Integer stuAge) {
            this.stuAge = stuAge;
        }
    
        public String getStuMajor() {
            return stuMajor;
        }
    
        public void setStuMajor(String stuMajor) {
            this.stuMajor = stuMajor;
        }
    
        @Override
        public String toString() {
            return "Student{" +
                    "stuId=" + stuId +
                    ", stuName='" + stuName + '\'' +
                    ", stuAge=" + stuAge +
                    ", stuMajor='" + stuMajor + '\'' +
                    '}';
        }
    }

### 创建接口和对应的Mapper.xml ###

public interface StudentMapper {
        public Student getStudent(Integer stuid);
        public Integer deleteStudent(Integer stuid);
        public Integer insertStudent(Student sut);
    
    }

StudentMapper.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.cyh.mapper.StudentMapper">
            <select id="getStudent" parameterType="java.lang.Integer" resultType="com.cyh.pojo.Student">
                select * from student where stuId = #{stuId}
            </select>
    
            <insert id="insertStudent" parameterType="com.cyh.pojo.Student">
                insert into student(stuName, stuAge, stuMajor) values(#{stuName},#{stuAge},#{stuMajor})
            </insert>
    
            <delete id="deleteStudent" parameterType="java.lang.Integer">
                delete FROM student WHERE stuid = #{stuid}
            </delete>
    
        </mapper>

### 测试 ###

测试方法通过SqlSessionFactoryUtil创建sqlSession， 在得到指定的Mapper进行操作

@Test
        public void test() throws IOException {
            SqlSession sqlSession = null;
            try {
               sqlSession = SqlSessionFactoryUtil.openSqlSession();
               StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);
               Student stu = new Student();
               stu.setStuName("王五");
               stu.setStuAge(12);
               stu.setStuMajor("软件");
    
               studentMapper.insertStudent(stu);
               studentMapper.deleteStudent(1);
    
               sqlSession.commit();
            } catch (Exception e){
                e.printStackTrace();
            }finally {
                if (sqlSession != null){
                    sqlSession.close();
                }
            }
        }

### 添加log4j ###

在maven中添加依赖

在resources目录下新建log4j.properties内容如下

log4j.rootLogger=DEBUG, Console
    #Console 
    log4j.appender.Console=org.apache.log4j.ConsoleAppender  
    log4j.appender.Console.layout=org.apache.log4j.PatternLayout  
    log4j.appender.Console.layout.ConversionPattern=%d [%t] %-5p [%c] - %m%n  
    
    log4j.logger.java.sql.ResultSet=INFO  
    log4j.logger.org.apache=INFO  
    log4j.logger.java.sql.Connection=DEBUG  
    log4j.logger.java.sql.Statement=DEBUG  
    log4j.logger.java.sql.PreparedStatement=DEBUG

执行测试类方法控制台打印如下：

2018-03-13 09:35:48,595 [main] DEBUG [com.cyh.mapper.StudentMapper.insertStudent] - ooo Using Connection [com.mysql.jdbc.JDBC4Connection@5de164e4]
      2018-03-13 09:35:48,597 [main] DEBUG [com.cyh.mapper.StudentMapper.insertStudent] - ==>  Preparing: insert into student(stuName, stuAge, stuMajor) values(?,?,?) 
      2018-03-13 09:35:48,637 [main] DEBUG [com.cyh.mapper.StudentMapper.insertStudent] - ==> Parameters: 王五(String), 12(Integer), 软件(String)
      2018-03-13 09:35:48,642 [main] DEBUG [com.cyh.mapper.StudentMapper.deleteStudent] - ooo Using Connection [com.mysql.jdbc.JDBC4Connection@5de164e4]
      2018-03-13 09:35:48,642 [main] DEBUG [com.cyh.mapper.StudentMapper.deleteStudent] - ==>  Preparing: delete FROM student WHERE stuid = ? 
      2018-03-13 09:35:48,642 [main] DEBUG [com.cyh.mapper.StudentMapper.deleteStudent] - ==> Parameters: 1(Integer)