（四）关于Mybatis别名定义
代码托管在github上【https://github.com/Damaer/Mybatis-Learning】的mybatis-04
在前面的例子中（三）Mybatis使用工具类读取配置文件以及从属性读取DB信息，我们改进了两点：使用工具类获取sqlSession以及从属性中读取数据库信息，那么我们下面需要改进的是别名，也趁这个机会介绍一下别名的作用。
其实在我们实际开发中，大多数情况下，一个mapper.xml文件对应的是对一个对象的操作，当前的mapper如下：
<mapper namespace="mapper1">
<insert id="insertStudent" parameterType="bean.Student">
insert into student(name,age,score) values(#{name},#{age},#{score})
insert>
mapper>我们可以看出parameterType有时候会写很长很长，每写一个sql我们就要使用parameterType传值或者使用返回类型，意思就是这个parameterType太长了，有没有什么办法可以让我们就写类名就可以了，其实是有的！！！那就是别名，mybatis可以让我们起一个别名给它，别名定义是在mybatis.xml主配置文件中。注意别名标签应该定义在后面，在前面，顺序不能颠倒。
<typeAliases>
<typeAlias type="bean.Student" alias="Student"/>
typeAliases>我们在上面的别名中的意思是给bean包下Student这个类起了一个别名，名字叫Student，那么我们就可以使用了，很简单：
<mapper namespace="mapper1">
<insert id="insertStudent" parameterType="Student">
insert into student(name,age,score) values(#{name},#{age},#{score})
insert>
mapper>但是要是bean里面有很多类，我们是不是要写很多别名呢？其实不用，我们可以观察到
<typeAliases>
<package name="bean"/>
typeAliases>贴代码
在这里贴一下代码，代码结构如下：
bean包下的Student类：
package bean;
public class Student {
private Integer id;
private String name;
private int age;
private double score;
public Student(){
}
public Student(String name, int age, double score) {
super();
this.name = name;
this.age = age;
this.score = score;
}
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;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public double getScore() {
return score;
}
public void setScore(double score) {
this.score = score;
}
@Override
public String toString() {
return "Student [id=" + id + ", name=" + name + ", age=" + age
+ ", score=" + score + "]";
}
}
dao包下面的IStudentDao接口：
package dao;
import bean.Student;
public interface IStudentDao {
public void insertStu(Student student);
}
dao包下的实现类：
import bean.Student;
import org.apache.ibatis.session.SqlSession;
import utils.MyBatisUtils;
public class StudentDaoImpl implements IStudentDao {
private SqlSession sqlSession;
public void insertStu(Student student) {
//加载主配置文件
try {
sqlSession=MyBatisUtils.getSqlSession();
sqlSession.insert("mapper1.insertStudent",student);
sqlSession.commit();
} finally{
if(sqlSession!=null){
sqlSession.close();
}
}
}
}util包下面的工具类：
public class MyBatisUtils {
/* public SqlSession getSqlSession(){
InputStream is;
try {
is = Resources.getResourceAsStream("mybatis.xml");
return new SqlSessionFactoryBuilder().build(is).openSession();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}*/
static private SqlSessionFactory sqlSessionFactory;
static public SqlSession getSqlSession() {
InputStream is;
try {
is = Resources.getResourceAsStream("mybatis.xml");
if (sqlSessionFactory == null) {
sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);
}
return sqlSessionFactory.openSession();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
}resource资源目录下mapper目录下的mapper.xml(mapper1.xml也一样内容，只是里面namespace不一样)：
<mapper namespace="mapper1">
<insert id="insertStudent" parameterType="Student">
insert into student(name,age,score) values(#{name},#{age},#{score})
insert>
mapper>jdbc_mysql.properties文件（jdbc_oracle.properties是空文件）：
jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/test
jdbc.user=root
jdbc.password=123456log4j.properties
log4j.prpp
log4j.rootLogger=DEBUG, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=[service] %d - %c -%-4r [%t] %-5p %c %x - %m%n
log4j.logger.java.sql.Statement = debug
log4j.logger.java.sql.PreparedStatement = debug
log4j.logger.java.sql.ResultSet =debug主配置文件mybatis.xml:
<configuration>
<properties resource="jdbc_mysql.properties">
properties>
<typeAliases>
<package name="bean"/>
typeAliases>
<environments default="mysqlEM">
<environment id="mysqlEM">
<transactionManager type="JDBC">
transactionManager>
<dataSource type="POOLED">
<property name="driver" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.user}"/>
<property name="password" value="${jdbc.password}"/>
dataSource>
environment>
environments>
<mappers>
<mapper resource="mapper/mapper.xml"/>
<mapper resource="mapper/mapper1.xml"/>
mappers>
configuration>test.sql
#创建数据库
CREATE DATABASE `test` DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci;
#创建数据表
CREATE TABLE `student` ( `id` INT NOT NULL AUTO_INCREMENT , `name` VARCHAR(20) NOT NULL ,
`age` INT NOT NULL , `score` DOUBLE NOT NULL , PRIMARY KEY (`id`)) ENGINE = MyISAM;测试文件MyTest.java:
public class MyTest {
private IStudentDao dao;
@Before
public void Before(){
dao=new StudentDaoImpl();
}
@Test
public void testInsert(){
Student student=new Student("1ADAS",23,100);
dao.insertStu(student);
}
}Maven配置文件pom.xml:
<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>4.0.0modelVersion>
<groupId>com.testgroupId>
<artifactId>testartifactId>
<version>1.0-SNAPSHOTversion>
<dependencies>
<dependency>
<groupId>org.mybatisgroupId>
<artifactId>mybatisartifactId>
<version>3.3.0version>
dependency>
<dependency>
<groupId>mysqlgroupId>
<artifactId>mysql-connector-javaartifactId>
<version>5.1.29version>
dependency>
<dependency>
<groupId>junitgroupId>
<artifactId>junitartifactId>
<version>4.11version>
<scope>testscope>
dependency>
<dependency>
<groupId>log4jgroupId>
<artifactId>log4jartifactId>
<version>1.2.17version>
dependency>
<dependency>
<groupId>org.slf4jgroupId>
<artifactId>slf4j-apiartifactId>
<version>1.7.12version>
dependency>
<dependency>
<groupId>org.slf4jgroupId>
<artifactId>slf4j-log4j12artifactId>
<version>1.7.12version>
dependency>
dependencies>
project>至此，整个项目的代码结束。