第二章 MyBatis入门
1.Junit的使用
在maven中导入junit依赖：
junit
junit
4.11
test
注解的用法：
@Test:表示一个可以独立运行的单元测试方法；
@Before:在每个单元测试方法执行之前运行;
@After：在每个单元测试方法之后运行；
@BeforeClass:使用该注解的方法必须是静态方法，会在所有单元测试方法运行之前执行一次；
@AfterClass:必须是静态方法，会在所有单元测试方法之后运行一次。
2. MyBatis
2.1 ORM思想
ORM(对象关系映射 Object Relational Mapping)是通过描述对象和数据库之间映射的元数据，将程序中的对象自动持久化到关系数据库中。
通过自定义注解和反射实现简单的orm:
自定义注解：
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface ColumnInformation {
String colName();
String colType();
int colSize() default 20;
}import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface PrimaryKey {
boolean isAutoIncrement();
}import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface Table {
String tableName();
}给实体对象的添加注解：
student：
import com.wen.annotation.ColumnInformation;
import com.wen.annotation.PrimaryKey;
import com.wen.annotation.Table;
import java.util.Date;
@Table(tableName = "student")
public class Student {
@PrimaryKey(isAutoIncrement = true)
@ColumnInformation(colName = "s_id",colType = "int",colSize = 11)
private Integer s_id;
@ColumnInformation(colName = "s_name",colType = "varchar",colSize = 10)
private String s_name;
@ColumnInformation(colName = "s_birth",colType = "date")
private Date s_birth;
@ColumnInformation(colName = "s_sex",colType = "char",colSize = 1)
private String s_sex;
public Student() {
}
public Student(Integer s_id, String s_name, Date s_birth, String s_sex) {
this.s_id = s_id;
this.s_name = s_name;
this.s_birth = s_birth;
this.s_sex = s_sex;
}
public Student(String s_name, Date s_birth, String s_sex) {
this.s_name = s_name;
this.s_birth = s_birth;
this.s_sex = s_sex;
}
public Integer getS_id() {
return s_id;
}
public void setS_id(Integer s_id) {
this.s_id = s_id;
}
public String getS_name() {
return s_name;
}
public void setS_name(String s_name) {
this.s_name = s_name;
}
public Date getS_birth() {
return s_birth;
}
public void setS_birth(Date s_birth) {
this.s_birth = s_birth;
}
public String getS_sex() {
return s_sex;
}
public void setS_sex(String s_sex) {
this.s_sex = s_sex;
}
@Override
public String toString() {
return "Student{" +
"s_id=" + s_id +
", s_name='" + s_name + '\'' +
", s_birth=" + s_birth +
", s_sex='" + s_sex + '\'' +
'}';
}
}score：
import com.wen.annotation.ColumnInformation;
import com.wen.annotation.PrimaryKey;
import com.wen.annotation.Table;
@Table(tableName = "score")
public class Score {
@PrimaryKey(isAutoIncrement = true)
@ColumnInformation(colName = "s_id",colType = "int",colSize = 20)
private Integer s_id;
@ColumnInformation(colName = "c_id",colType = "int",colSize = 20)
private Integer c_id;
@ColumnInformation(colName = "s_score",colType = "decimal",colSize = 3)
private Double s_score;
public Score() {
}
public Score(Integer s_id, Integer c_id, Double s_score) {
this.s_id = s_id;
this.c_id = c_id;
this.s_score = s_score;
}
public Integer getS_id() {
return s_id;
}
public void setS_id(Integer s_id) {
this.s_id = s_id;
}
public Integer getC_id() {
return c_id;
}
public void setC_id(Integer c_id) {
this.c_id = c_id;
}
public Double getS_score() {
return s_score;
}
public void setS_score(Double s_score) {
this.s_score = s_score;
}
@Override
public String toString() {
return "Score{" +
"s_id=" + s_id +
", c_id=" + c_id +
", s_score=" + s_score +
'}';
}
}orm实现：
inteeface:
import java.util.List;
import java.util.Map;
public interface IGenericDao {
/**
* 查询全部数据
* @param t
* @return
*/
List> listAll(T t);
/**
* 插入数据
* @param t
* @return
*/
int insert(T t);
/**
* 修改数据
* @param t
* @return
*/
int update(T t);
/**
* 删除数据
* @param t
* @return
*/
int delete(T t);
}
impl:
import com.wen.annotation.ColumnInformation;
import com.wen.annotation.PrimaryKey;
import com.wen.annotation.Table;
import com.wen.orm.dao.IGenericDao;
import com.wen.orm.util.BaseDao;
import java.beans.IntrospectionException;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.List;
import java.util.Map;
public class GenericDaoImpl implements IGenericDao {
private String getSql(Class t,String sign) {
StringBuilder sql = new StringBuilder();
if(t.isAnnotationPresent(Table.class)){
Table table = (Table) t.getAnnotation(Table.class);
Field[] declaredFields = t.getDeclaredFields();
StringBuilder colSql = new StringBuilder();
int count = 0;
String colNameByPrimaryKey ="";
switch (sign){
case "selectAll":
sql.append("select ");
for (Field f:declaredFields) {
ColumnInformation annotation = f.getAnnotation(ColumnInformation.class);
colSql.append(annotation.colName()+",");
}
sql.append(colSql.substring(0,colSql.length()-1)).append(" from ").append(table.tableName());
break;
case "insert":
sql.append("insert into ");
sql.append(table.tableName());
sql.append("(");
for (Field f:declaredFields) {
if(f.isAnnotationPresent(PrimaryKey.class)){
continue;
}
ColumnInformation annotation = f.getAnnotation(ColumnInformation.class);
colSql.append(annotation.colName()+",");
count++;
}
sql.append(colSql.substring(0,colSql.length()-1));
sql.append(") value (?");
for (int i = 0; i < count-1; i++) {
sql.append(",?");
}
sql.append(")");
break;
case "update":
sql.append("update ");
sql.append(table.tableName());
sql.append(" set ");
for (Field f:declaredFields) {
ColumnInformation annotation = f.getAnnotation(ColumnInformation.class);
if(f.isAnnotationPresent(PrimaryKey.class)){
colNameByPrimaryKey = annotation.colName();
continue;
}
colSql.append(annotation.colName()+"= ?,");
}
sql.append(colSql.substring(0,colSql.length()-1));
sql.append(" where "+colNameByPrimaryKey+"= ?");
break;
case "delete":
sql.append("delete from ");
sql.append(table.tableName());
for (Field f:declaredFields) {
ColumnInformation annotation = f.getAnnotation(ColumnInformation.class);
if(f.isAnnotationPresent(PrimaryKey.class)){
colNameByPrimaryKey = annotation.colName();
break;
}
}
sql.append(" where "+colNameByPrimaryKey+"= ?");
break;
default:
break;
}
}
return sql.toString();
}
@Override
public List> listAll(T t) {
String sql = getSql(t.getClass(),"selectAll");
System.out.println(sql);
return BaseDao.executeQuery(sql,null);
}
@Override
public int insert(T t) {
Class aClass = t.getClass();
String sql = getSql(aClass,"insert");
System.out.println(sql);
Field[] declaredFields = aClass.getDeclaredFields();
Object[] params = new Object[declaredFields.length];
int i = 0;
for (Field field:declaredFields) {
if(field.isAnnotationPresent(PrimaryKey.class)){
continue;
}
try {
PropertyDescriptor propertyDescriptor = new PropertyDescriptor(field.getName(), aClass);
Method readMethod = propertyDescriptor.getReadMethod();
params[i++] = readMethod.invoke(t);
} catch (IntrospectionException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
}
System.out.println(i);
Object[] newParams = new Object[i];
System.arraycopy(params,0,newParams,0,i);
for (Object o :newParams) {
System.out.println(o);
}
return BaseDao.executeUpdate(sql,newParams);
}
@Override
public int update(T t) {
Class aClass = t.getClass();
String sql = getSql(aClass,"update");
System.out.println(sql);
Field[] declaredFields = aClass.getDeclaredFields();
Object oByPrimaryKey = "";
Object[] params = new Object[declaredFields.length];
int i = 0;
for (Field f:declaredFields) {
try {
PropertyDescriptor propertyDescriptor = new PropertyDescriptor(f.getName(), aClass);
if(f.isAnnotationPresent(PrimaryKey.class)){
oByPrimaryKey = propertyDescriptor.getReadMethod().invoke(t);
}else {
params[i++] = propertyDescriptor.getReadMethod().invoke(t);
}
} catch (IntrospectionException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
}
params[i] = oByPrimaryKey;
for (Object o: params) {
System.out.println(o);
}
return BaseDao.executeUpdate(sql,params);
}
@Override
public int delete(T t) {
Class aClass = t.getClass();
String sql = getSql(aClass,"delete");
System.out.println(sql);
Field[] declaredFields = aClass.getDeclaredFields();
Object[] params = null;
for (Field f:declaredFields) {
if(f.isAnnotationPresent(PrimaryKey.class)){
try {
params = new Object[]{new PropertyDescriptor(f.getName(),aClass).getReadMethod().invoke(t)};
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
} catch (IntrospectionException e) {
e.printStackTrace();
}
}
}
System.out.println(params[0]);
return BaseDao.executeUpdate(sql,params);
}
} 测试：
import com.wen.entity.Score;
import com.wen.entity.Student;
import com.wen.orm.dao.IGenericDao;
import com.wen.orm.dao.impl.GenericDaoImpl;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.List;
import java.util.Map;
public class Test {
public static void main(String[] args) throws ParseException {
IGenericDao genericDao = new GenericDaoImpl();
Student student = new Student();
Score score = new Score(8,3,98.0);
student.setS_id(15);
student.setS_name("小温");
student.setS_birth(new SimpleDateFormat("yyyy-MM-dd").parse("2008-1-1"));
student.setS_sex("男");
//genericDao.insert(student);
//genericDao.insert(score);
//genericDao.update(student);
genericDao.delete(student);
//genericDao.delete(score);
System.out.println("======================");
List> list = genericDao.listAll(student);
for (Map map:list) {
System.out.println(map);
}
}
}
2.2 MyBatis简介
一个基于Java的持久层/数据访问层框架。
2.3 结构
①接口层：给应用程序提供一系列的数据接口；
②接口层传递参数：sql命令，在数据处理曾进行处理，返回对应的结果映射；
③基础支撑层：提供最基础的底层的操作：连接管理(连接池),事务管理(增、删、该)，配置加载(读取配置信息)，缓存(一级缓存，二级缓存)
2.4 环境搭建
整体结构：
Mybatis官网：mybatis – MyBatis 3 | 入门
①建立maven项目，导入需要的jar包；
pom.xml：
org.mybatis
mybatis
3.5.7
mysql
mysql-connector-java
8.0.11
junit
junit
4.11
test
②创建配置数据库连接信息的properties文件；
db.properties：
jdbc.driver = com.mysql.cj.jdbc.Driver
jdbc.url = jdbc:mysql://127.0.0.1:3306/***?useSSL=false&characterEncoding=utf-8&serverTimezone=Asia/Shanghai
jdbc.userName =
jdbc.password = ③配置数据库连接属性和mybati日志；
Mybatis.xml:
配置文件的属性是有序的，顺序不对会直接报错；
④在mapper包下创建对应实体的mapper接口(GoodsMapper.java)
import com.entity.Goods;
import com.entity.PageInfo;
import java.util.List;
import java.util.Map;
public interface GoodsMapper {
/**
* 两表查询，包含商品种类
* @return
*/
List⑤在mapper包下创建对应实体的mapper文件(GoodsMapper.xml)
采用mapper接口开发的方式时，要注意：
①配置文件和其对应的接口，除了文件类型不同，其他的完全相同；
②resources中创建多级目录要用“/”来分割，不能用“.”；
③xml文件中对应的查询语句的"id"要与对应接口的方法名完全一致;
④返回的结果的类型或参数的类型，如果是自己创建的类型需要写完整，或者在MyBatis.xml中配置好别名；
⑤在sql语句中有多个参数时，名称要与传入的一致。
insert into tb_goods(goods_name,price,produce_date,address,category_id)
values
(#{goods.goodsName}, #{goods.price}, #{goods.produceDate}, #{goods.address}, #{goods.categoryId})
delete from tb_goods where goods_id = #{id}
truncate tb_goods;
⑥ 使用mybatis完成crud
import com.dao.IGoodsDao;
import com.entity.Goods;
import com.entity.PageInfo;
import com.mapper.GoodsMapper;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import java.util.Map;
public class GoodsDaoImpl implements IGoodsDao {
/**
* 创建一个SqlSession的工厂用于创建sqlSession对象
*/
private static SqlSessionFactory sessionFactory;
static{
try {
InputStream resourceAsStream = Resources.getResourceAsStream("Mybatis.xml");
sessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
} catch (IOException e) {
e.printStackTrace();
}
}
@Override
public List⑦mybatis的事务
mybatis默认情况下是手动事务，在进行增删改操作之后要提交事务：
①提交：sqlSession.commit();
②设置自动事务:
在MyBatis.xml中，修改transactionManager配置为：
创建sqlSession时，openSession()设置为true,默认为false：
sessionFactory.openSession(true)。