public class JdbcTest {
public static void main(String[] args) {
Member condition = new Member();
condition.setName("Tom");
condition.setAge(19);
List<?> result = select(condition);
System.out.println(Arrays.toString(result.toArray()));
}
private static List<?> select(Object condition) {
List<Object> result = new ArrayList<>();
Class<?> entityClass = condition.getClass();
Connection con = null;
PreparedStatement pstm = null;
ResultSet rs = null;
try {
//1、加载驱动类
Class.forName("com.mysql.jdbc.Driver");
//2、建立连接
con = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/gp-vip-spring-db-demo?characterEncoding=UTF-8&rewriteBatchedStatements=true","root","123456");
//根据类名找属性名
Map<String,String> columnMapper = new HashMap<String,String>();
//根据属性名找字段名
Map<String,String> fieldMapper = new HashMap<String,String>();
Field[] fields = entityClass.getDeclaredFields();
for (Field field : fields) {
field.setAccessible(true);
String fieldName = field.getName();
if(field.isAnnotationPresent(Column.class)){
Column column = field.getAnnotation(Column.class);
String columnName = column.name();
columnMapper.put(columnName,fieldName);
fieldMapper.put(fieldName,columnName);
}else {
//默认就是字段名属性名一致
columnMapper.put(fieldName, fieldName);
fieldMapper.put(fieldName,fieldName);
}
}
//3、创建语句集
Table table = entityClass.getAnnotation(Table.class);
String sql = "select * from " + table.name();
StringBuffer where = new StringBuffer(" where 1=1 ");
for (Field field : fields) {
Object value =field.get(condition);
if(null != value){
if(String.class == field.getType()) {
where.append(" and " + fieldMapper.get(field.getName()) + " = '" + value + "'");
}else{
where.append(" and " + fieldMapper.get(field.getName()) + " = " + value + "");
}
//其他的，在这里就不一一列举，下半截我们手写ORM框架会完善
}
}
System.out.println(sql + where.toString());
pstm = con.prepareStatement(sql + where.toString());
//4、执行语句集
rs = pstm.executeQuery();
//元数据？
//保存了处理真正数值以外的所有的附加信息
int columnCounts = rs.getMetaData().getColumnCount();
while (rs.next()){
Object instance = entityClass.newInstance();
for (int i = 1; i <= columnCounts; i++) {
//实体类 属性名，对应数据库表的字段名
//可以通过反射机制拿到实体类的说有的字段
//从rs中取得当前这个游标下的类名
String columnName = rs.getMetaData().getColumnName(i);
//有可能是私有的
Field field = entityClass.getDeclaredField(columnMapper.get(columnName));
field.setAccessible(true);
field.set(instance,rs.getObject(columnName));
}
result.add(instance);
}
//5、获取结果集
}catch (Exception e){
e.printStackTrace();
}
//6、关闭结果集、关闭语句集、关闭连接
finally {
try {
rs.close();
pstm.close();
con.close();
}catch (Exception e){
e.printStackTrace();
}
}
return result;
}
}public class OrmTest {
private SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMddHHmmdd");
@Autowired private MemberDao memberDao;
@Autowired private OrderDao orderDao;
//ORM（对象关系映射 Object Relation Mapping）
//Hibernate/Spring JDBC/MyBatis/JPA 一对多、多对多、一对一
//Hibernate 全自动档 不需要写一句SQL语句
//MyBatis 半自动（手自一体） 支持简单的映射，复杂关系，需要自己写SQL
//Spring JDBC 全手动挡，所有的SQL都要自己写，它帮我们设计了一套标准 模板模式
//为什么有了MyBatis我还要自己的手写ORM框架呢？
//1、用MyBatis，我可控性无法保证
//2、我有不敢用Hibernate，高级玩家玩的，
//3、没有时间自己从0到1写一个ORM框架
//4、站在巨人的肩膀上再升级，做二次开发
//约定优于配置
//1、先制定顶层接口,参数返回值全部统一
// List<?> Page<?> select(QueryRule queryRule)
// Int delete(T entity) entity中的ID不能为空，如果ID为空，其他条件不能为空，都为空不予执行
// ReturnId insert(T entity) 只要entity不等于null
// Int update(T entity) entity中的ID不能为空，如果ID为空，其他条件不能为空，都为空不予执行
//基于JDBC封装了一套
//基于Redis封装了一套
//基于MongoDB
//基于ElasticSearch
//基于Hive
//基于HBase
//QueryRule
@Test
public void testSelectAllForMember(){
try {
List<Member> result = memberDao.selectAll();
System.out.println(Arrays.toString(result.toArray()));
} catch (Exception e) {
e.printStackTrace();
}
}
@Test
@Ignore
public void testInsertMember(){
try {
for (int age = 25; age < 35; age++) {
Member member = new Member();
member.setAge(age);
member.setName("Tom");
member.setAddr("Hunan Changsha");
memberDao.insert(member);
}
}catch (Exception e){
e.printStackTrace();
}
}
@Test
// @Ignore
public void testInsertOrder(){
try {
Order order = new Order();
order.setMemberId(1L);
order.setDetail("历史订单");
Date date = sdf.parse("20180201123456");
order.setCreateTime(date.getTime());
orderDao.insertOne(order);
}catch (Exception e){
e.printStackTrace();
}
}
}