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为了方便使用sql的数据#xff0c;在查询后mysql会把数据封装到java里面的resultset对象#xff0c;然后我们需要把resultset里的数据再封装到我们自己创建的对象中#xff0c;比如Student对象#xff1a;
public class Student {int number;String n…java查询结果的处理
为了方便使用sql的数据在查询后mysql会把数据封装到java里面的resultset对象然后我们需要把resultset里的数据再封装到我们自己创建的对象中比如Student对象
public class Student {int number;String name;String gender;Date birthday;String phone;double height;Timestamp reg_time;public void setNumber(int number) {this.number number;}public void setName(String name) {this.name name;}public void setGender(String gender) {this.gender gender;}public void setBirthday(Date birthday) {this.birthday birthday;}public void setPhone(String phone) {this.phone phone;}public void setHeight(double height) {this.height height;}public void setReg_time(Timestamp reg_time) {this.reg_time reg_time;}public int getNumber() {return number;}public String getName() {return name;}public String getGender() {return gender;}public Date getBirthday() {return birthday;}public String getPhone() {return phone;}public double getHeight() {return height;}public Timestamp getReg_time() {return reg_time;}Overridepublic String toString() {return Student{ number number , name name , gender gender , birthday birthday , phone phone , height height , reg_time reg_time };}
}把数据从resultset转到student中要使用rs的get的一系列函数可以有getintgetstring等等它的参数是对应的sql的列
public static Student findStudentByNumber(int number) throws SQLException {DriverManager.registerDriver(new Driver());String urljdbc:mysql://127.0.0.1:3306/schooldb?serverTimezoneAsia/Shanghai;String userroot; //账户String psdroot; //密码//建立与数据库的连接Connection connectionDriverManager.getConnection(url,user,psd);PreparedStatement psconnection.prepareStatement(select number,name,gender,birthday,height,phone,reg_time from student where number?);ps.setObject(1,number);//换行查询后mysql将数据封装到一个resultset对象中ResultSet rsps.executeQuery();////将resultset中的数据重新包装到我没自己的对象Student中使用起来更方便Student studentnew Student();while(rs.next()){ //查看resultset集合中下一组数据存在与否存在则返回true循环继续student.setNumber(rs.getInt(number));student.setName(rs.getString(name));student.setGender(rs.getString(gender));student.setBirthday(rs.getDate(birthday));student.setHeight(rs.getDouble(height));student.setPhone(rs.getString(phone));student.setReg_time(rs.getTimestamp(reg_time));}return student;}上面只是放在一个student中然而会有很多的student所以要创建一个student数组返回的时候返回student数组。
ArrayList students new ArrayList();while (rs.next()) { //查看resultset集合中下一组数据存在与否存在则返回true循环继续Student student new Student(); //放在循环里可以保证每次set的是不同的studentstudent.setNumber(rs.getInt(number));student.setName(rs.getString(name));student.setGender(rs.getString(gender));student.setBirthday(rs.getDate(birthday));student.setHeight(rs.getDouble(height));student.setPhone(rs.getString(phone));student.setReg_time(rs.getTimestamp(reg_time));students.add(student);}students放在循环外面student类放在循环里面每次在循环里新创建一个student对象然后添加进students里。
如果要检查sql中是否存在某个数据需要设置一个返回值boolean的方法返回的时候返回resultset.next()这个方法把resultset指向第一组数据再次调用会指向第二组数据以此类推然后返回当前组数据是否存在
private static boolean checkNum(int number) throws SQLException {DriverManager.registerDriver(new Driver());String urljdbc:mysql://127.0.0.1:3306/schooldb?serverTimezoneAsia/Shanghai;String userroot; //账户String psdroot; //密码//建立与数据库的连接Connection connectionDriverManager.getConnection(url,user,psd);PreparedStatement psconnection.prepareStatement(select number from student where number ?);ps.setObject(1,number);ResultSet resultSetps.executeQuery();return resultSet.next();}也可以改变查询方法比如查询number出现的次数count(*) as c大于等于1说明number存在于这个表中为0的话说明不存在返回值返回rs.getint(“c”)
private static int checkNum(int number) throws SQLException {DriverManager.registerDriver(new Driver());String urljdbc:mysql://127.0.0.1:3306/schooldb?serverTimezoneAsia/Shanghai;String userroot; //账户String psdroot; //密码//建立与数据库的连接Connection connectionDriverManager.getConnection(url,user,psd);PreparedStatement psconnection.prepareStatement(select count(*) c from student where number ?);ps.setObject(1,number);ResultSet resultSetps.executeQuery();resultSet.next();return resultSet.getInt(c);}但是next方法是必须要加上的必须要将指针指向rs的第一组数据
