踩坑ResultSet.wasNull()
必须先读取该列，然后使用 ResultSet.wasNull 方法检查该次读取是否返回 JDBC NULL。不然结果返回值不会是对应类型，而是null
1.新建项目（java）JDBCDome
2.新建包（lib）
导入两个JAR
（1）连接数据库
（2）测试的JAR@Test
3.新建一个包jdbc.pojo
User实体类
public class User{
private Long id;
private String userName;
private String passWord;
// set,get方法
}4.新建一个包jdbc.connection
数据库链接类Connection
public class Connection{
//数据驱动
private String driver="com.mysql.jdbc.Driver";
//链接本机数据库
private String url="jdbc:mysql://localhost:3306/数据库";
private String userName="数据库名";
private String passWord="数据库密码";
private Connection connection=null;
public Connection getConnection(){
try {
Class.forName(driver);
connection= DriverManager.getConnection(url,userName,passWord);
} catch (ClassNotFoundException e) {
e.printStackTrace();
System.out.println("数据库加载错误");
} catch (SQLException e) {
e.printStackTrace();
System.out.println("数据库加载错误");
}
return connection;
}
}数据资源类jdbcDataSource类
public class jdbcDataSource{
//增删改查
JdbcConnectin jdbcConnectin=new JdbcConnectin();
Connection connection=jdbcConnectin.getConnection();
PreparedStatement ps=null;//执行sql语句
//数据插入方法
public void insertUser(User user){
String insertUserSql="insert into db_user (user_name,password) values(?,?)";
try {
ps=connection.prepareStatement(insertUserSql);
ps.setString(1, user.getUserName());//=?(1)
ps.setString(2, user.getPassWord());
ps.executeUpdate();//刷新数据库
} catch (SQLException e) {
e.printStackTrace();
System.out.println("插入用户错误");
}finally {
try {
ps.close();
} catch (SQLException e) {
e.printStackTrace();
System.out.println("预编译语句编译错误");
}
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
System.out.println("关闭数据连接错误");
}
}
}
/**
* 根据id删除用户
*
* @param id
*/
public void deleteUser(Integer id) {
String deleteUserSql = "delete from user where id=?";
try {
ps = connection.prepareStatement(deleteUserSql);
ps.setInt(1, id);
ps.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
System.out.println("数据插入失败");
} finally {
if (ps != null) {
try {
ps.close();
} catch (SQLException e) {
e.printStackTrace();
System.out.println("资源关闭异常");
}
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
System.out.println("数据库连接关闭异常");
}
}
}
}
/**
* 更新用户信息
*
* @param user
*/
public void updateUser(User user) {
String updateUserSql = "update user set user_name=?,pass_word=?where id=?";
try {
ps = connection.prepareStatement(updateUserSql);
ps.setString(1, user.getUserName());
ps.setString(2, user.getPassWord());
ps.setInt(3, user.getId());
ps.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
System.out.println("数据插入失败");
} finally {
if (ps != null) {
try {
ps.close();
} catch (SQLException e) {
e.printStackTrace();
System.out.println("资源关闭异常");
}
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
System.out.println("数据库连接关闭异常");
}
}
}
}
public List<User> findAllUser() {
List<User> users = new ArrayList<User>();
String selectAllUserSql = "SELECT *from user";
try {
ps = connection.prepareStatement(selectAllUserSql);
ResultSet rs = ps.executeQuery();
while (rs.next()) {
User user = new User();
user.setId(rs.getInt(1));
user.setUserName(rs.getString(2));
user.setPassWord(rs.getString(3));
users.add(user);
}
} catch (SQLException e) {
e.printStackTrace();
System.out.println("数据插入失败");
} finally {
if (ps != null) {
try {
ps.close();
} catch (SQLException e) {
e.printStackTrace();
System.out.println("资源关闭异常");
}
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
System.out.println("数据库连接关闭异常");
}
}
}
return users;
}
}
4.进行程序测试
建包jdbc.test
Test类
public class Test{
//加载数据源
JdbcDataSource jdbcDataSource=new JdbcDataSource();
@Test//测试方法执行入口
public void findAllUser(){
List<User> users=new ArrayList<>();
users=jdbcDataSource.findAllUser();
for(User u:users){
System.out.println(u.getId());
}
}
@Test
public void updateUser(){
User user=new User();
user.setId(3);
user.setUserName("xiaohuang");
user.setPassWord("1212");
jdbcDataSource.updateUser(user);
}
@Test
public void deleteUser(){
int userId=2;
jdbcDataSource.deleteUser(userId);
}
@Test
public void insert(){
User user =new User();
user.setUserName("xiaoming");
user.setPassWord("123");
jdbcDataSource.insertUser(user);
User user =new User("xiaohua","123");
jdbcDataSource.insertUser(user);
}
}5.一个数据流程结束
