4天贯通JDBC技术七、实现DAO及其实现类CustomerDAO的代码
【DAO.java】
//DAO：database access object
class ReflectionUtils{
//获取clazz对象对应的运行时类的父类的泛型
public static Class getSuperGeneric(Class clazz){
Type type = clazz.getGenericSuperclass();
ParameterizedType p = (ParameterizedType)type;
Type[] ts = p.getActualTypeArguments();
return (Class)ts[0];
}
}
public class DAO<T> {
private Class<T> clazz = null;
//this.getClass()在这个问题中，就是CustomerDAO
public DAO(){
clazz = ReflectionUtils.getSuperGeneric(this.getClass());
}
//获取数据库的标准的特定含义的值
public <E> E getValue(Connection conn,String sql,Object...args){
PreparedStatement ps = null;
ResultSet rs = null;
try{
ps = conn.prepareStatement(sql);
for(int i = 0;i < args.length;i++){
ps.setObject(i + 1, args[i]);
}
rs = ps.executeQuery();
if(rs.next()){
return (E)rs.getObject(1);
}
}catch(Exception e){
e.printStackTrace();
}finally{
JDBCUtils.close(rs, ps, null);
}
return null;
}
//返回多个对象，以集合的形式返回
public List<T> getForList(Connection conn,String sql,Object ...args){
PreparedStatement ps = null;
ResultSet rs = null;
List<T> list = new ArrayList<>();
try{
//1.预编译sql语句，获取PreparedStatement对象
ps = conn.prepareStatement(sql);
//2.填充占位符
for(int i = 0;i < args.length;i++){
ps.setObject(i + 1, args[i]);
}
//3.返回一个结果集
rs = ps.executeQuery();
ResultSetMetaData rsmd = rs.getMetaData();
int columnCount = rsmd.getColumnCount();
while(rs.next()){
T t = clazz.newInstance();
//给t对象的相应属性赋值
for(int i = 0;i < columnCount;i++){
Object columnVal = rs.getObject(i + 1);
String columnLabel = rsmd.getColumnLabel(i + 1);
PropertyUtils.setProperty(t, columnLabel, columnVal);
}
list.add(t);
}
}catch(Exception e){
e.printStackTrace();
}finally{
JDBCUtils.close(rs, ps, null);
}
//System.out.println(clazz);
return list;
}
//返回一个对象
public T get(Connection conn,String sql,Object ...args){
PreparedStatement ps = null;
ResultSet rs = null;
try{
//1.预编译sql语句，获取PreparedStatement对象
ps = conn.prepareStatement(sql);
//2.填充占位符
for(int i = 0;i < args.length;i++){
ps.setObject(i + 1, args[i]);
}
//3.返回一个结果集
rs = ps.executeQuery();
ResultSetMetaData rsmd = rs.getMetaData();
int columnCount = rsmd.getColumnCount();
if(rs.next()){
T t = clazz.newInstance();
//给t对象的相应属性赋值
for(int i = 0;i < columnCount;i++){
Object columnVal = rs.getObject(i + 1);
String columnLabel = rsmd.getColumnLabel(i + 1);
PropertyUtils.setProperty(t, columnLabel, columnVal);
}
return t;
}
}catch(Exception e){
e.printStackTrace();
}finally{
JDBCUtils.close(rs, ps, null);
}
//System.out.println(clazz);
return null;
}
//通用的增删改的操作
public void update(Connection conn,String sql,Object ... args){
PreparedStatement ps = null;
try{
ps = conn.prepareStatement(sql);
for(int i = 0;i < args.length;i++){
ps.setObject(i + 1, args[i]);
}
ps.executeUpdate();
}catch(Exception e){
e.printStackTrace();
}finally{
JDBCUtils.close(null, ps, null);
}
}
}
【CustomerDAO.java】
//CustomerDAO类是用来操作Customer类的
public class CustomerDAO extends DAO<Customer>{
// @Test
// public void testGeneric(){
// Class clazz = CustomerDAO.class;
// Type type = clazz.getGenericSuperclass();
// ParameterizedType p = (ParameterizedType)type;
// Type[] ts = p.getActualTypeArguments();
// System.out.println(ts[0]);
// }
/**
* 获取对应的表中的记录的个数
*/
public long getCount(Connection conn){
String sql = "select count(*) from customers";
return (long)getValue(conn, sql);
}
/**
* 返回customers表中的所有数据
* @param conn
* @return
*/
public List<Customer> getAll(Connection conn){
String sql = "select id,name,email,birth from customers";
return getForList(conn, sql);
}
/**
* 根据指定的id返回相应的对象
* @param conn
* @param customerId
*/
public Customer getInstance(Connection conn,int customerId){
String sql = "select id,name,email,birth from customers where id = ?";
return get(conn, sql, customerId);
}
/**
* 删除指定customerId的数据表中的记录
* @param conn
* @param customerId
*/
public void delete(Connection conn,int customerId){
String sql = "delete from customers where id = ?";
update(conn, sql, customerId);
}
/**
* 向数据表中修改指定id的信息为Customer对象的信息
* @param conn
* @param cust
*/
public void update(Connection conn,Customer cust){
String sql = "update customers set name = ?,email = ?,birth = ? where id = ?";
update(conn, sql, cust.getName(),cust.getEmail(),cust.getBirth(),cust.getId());
}
/**
* 向数据表中插入一条数据
* @param conn 数据库的连接
* @param cust 要插入的Customer对象
*/
public void insert(Connection conn,Customer cust){
String sql = "insert into customers(name,email,birth)values(?,?,?)";
update(conn, sql, cust.getName(),cust.getEmail(),cust.getBirth());
}
}
【TestCustomerDAO.java】
public class TestCustomerDAO {
CustomerDAO customerDAO = new CustomerDAO();
@Test
public void testGetCount(){
Connection conn = null;
try{
conn = JDBCUtils.getConnection();
long count = customerDAO.getCount(conn);
System.out.println(count);
}catch(Exception e){
e.printStackTrace();
}finally{
JDBCUtils.close(null, null, conn);
}
}
@Test
public void testGetAll(){
Connection conn = null;
try{
conn = JDBCUtils.getConnection();
List<Customer> list = customerDAO.getAll(conn);
//System.out.println(list);
Iterator<Customer> iterator = list.iterator();
while(iterator.hasNext()){
System.out.println(iterator.next());
}
}catch(Exception e){
e.printStackTrace();
}finally{
JDBCUtils.close(null, null, conn);
}
}
@Test
public void testQuery(){
Connection conn = null;
try{
conn = JDBCUtils.getConnection();
Customer cust = customerDAO.getInstance(conn, 13);
System.out.println(cust);
}catch(Exception e){
e.printStackTrace();
}finally{
JDBCUtils.close(null, null, conn);
}
}
@Test
public void testDelete(){
Connection conn = null;
try{
conn = JDBCUtils.getConnection();
customerDAO.delete(conn, 10);
}catch(Exception e){
e.printStackTrace();
}finally{
JDBCUtils.close(null, null, conn);
}
}
@Test
public void testUpdate(){
Connection conn = null;
try{
conn = JDBCUtils.getConnection();
Customer cust = new Customer(10, "张卫健", "zwj@gmail.com",new Date(new java.util.Date().getTime()));
customerDAO.update(conn, cust);
}catch(Exception e){
e.printStackTrace();
}finally{
JDBCUtils.close(null, null, conn);
}
}
@Test
public void testInsert(){
Connection conn = null;
try{
conn = JDBCUtils.getConnection();
Customer cust = new Customer(10, "张卫健", "zwj@gmail.com",new Date(new java.util.Date().getTime()));
customerDAO.insert(conn, cust);
}catch(Exception e){
e.printStackTrace();
}finally{
JDBCUtils.close(null, null, conn);
}
}
}
