java - 在Java中添加艺术家(人)时出错

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 7 年前。

我正在用 Java 创建一个软件，它应该能够注册艺术家、专辑和轨道。

一切都连接到 MySQL DB ，该软件只需要艺术家姓名，我向您展示我创建的方法。抱歉，很多名字都是西类牙语，但是这个是给我的学校的，我不能使用太多英语单词。我想你能理解

这是类(class)Conexión这使得连接到数据库:

public class Conexion {

Connection conexion=null;

/*Conectamos a la Base de Datos*/

public Conexion(){
    try{
        Class.forName("com.mysql.jdbc.Driver"); 
        conexion=DriverManager.getConnection("jdbc:mysql://localhost/chinook", "root", "");
    }catch(Exception excepcion){
        excepcion.printStackTrace();
    }
}

/*Devolvemos la conexion*/

public Connection getConnection(){
    return conexion;
}

/*Cerramos la conexión a la Base de Datos*/

public void desconectar(){
    try{
        conexion.close();
    }catch(Exception excepcion){
        excepcion.printStackTrace();
    }
 }

}

这是类(class)Coordinador ，这个类用于实现不同类之间的并集(遵循模型MVC)，我把添加艺术家的部分粘贴给你，其他的只是与 View 相关:

public void addArtista(ArtistaVO artistaVO){
    miLogica.validarRegistroArtista(artistaVO);
}

类(class)ArtistaVO我在其中创建艺术家的获取和设置:

public class ArtistaVO {

  private int idArtista;
  private String nombreArtista;

  public int getIdArtista(){
     return idArtista;
  }

  public void setIdArtista(int idArtista){
     this.idArtista=idArtista;
  }

  public String getNombreArtista(){
      return nombreArtista;
  }

  public void setNombreArtista(String nombreArtista){
     this.nombreArtista=nombreArtista;
  }
}

艺术家注册方法:

 public void addArtista(ArtistaVO artistaVO){

    Conexion conexion=new Conexion();

    try{
        //Insertamos los datos del Artista
        PreparedStatement  sqlAddArtist=conexion.getConnection().prepareStatement("INSERT into artist values(?,?)");
        ResultSet resultado=sqlAddArtist.executeQuery();
        while(resultado.next()){
            sqlAddArtist.setString(1, artistaVO.getNombreArtista());
            sqlAddArtist.setInt(2, getMaxId()+1);
        }
        JOptionPane.showMessageDialog(null, "Se ha añadido exitosamente","Información",JOptionPane.INFORMATION_MESSAGE);
        sqlAddArtist.close();
        conexion.desconectar();

    }catch(SQLException excepcion){
        System.out.println(excepcion.getMessage());
        JOptionPane.showMessageDialog(null,"No se registro", "Error", JOptionPane.ERROR_MESSAGE);
    }
}

该方法用于创建Artist ID:

  public int getMaxId(){
    int id=0;
    Conexion conexion=new Conexion();

    try{
        Statement sqlMaxId=conexion.getConnection().createStatement();
        ResultSet resultado=sqlMaxId.executeQuery("SELECT max(ArtistId) from artist");

        if(resultado.next()){
            id=resultado.getInt(0);
        }

        conexion.desconectar();
        sqlMaxId.close();
    }catch(SQLException excepcion){
        System.out.println(excepcion.getMessage());
    }

    return id;
}

这属于点击按钮后注册艺术家的窗口:

  public void actionPerformed(ActionEvent evento) {

    if(evento.getSource()==botonAñadir){

        try{
            ArtistaVO artistaVO=new ArtistaVO();
            artistaVO.setNombreArtista(campoTextoArtista.getText());

            miCoordinador.addArtista(artistaVO);
        }catch(Exception excepcion){
            JOptionPane.showMessageDialog(null, "Error al añadir Artista", "Error", JOptionPane.ERROR_MESSAGE);
        }
    }

}

我得到的错误是 Error al añadir Artista (添加艺术家时出错)，我不知道失败在哪里。

这是我得到的异常:

java.lang.NullPointerException
at controlador.Coordinador.addArtista(Coordinador.java:108)
at vista.VistaArtistasAdd.actionPerformed(VistaArtistasAdd.java:70)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

这是方法validarRegistroArtista :

 public void validarRegistroArtista(ArtistaVO artistaVO){
    ArtistaDAO artistaDAO;

    if(artistaVO.getIdArtista()>=0){
        artistaDAO=new ArtistaDAO();
        artistaDAO.addArtista(artistaVO);
    }else{
        JOptionPane.showMessageDialog(null, "Debe de introducirse algún numero de ID", "Advertencia", JOptionPane.WARNING_MESSAGE);
    }
}

Answer 1

您在绑定(bind)值之前执行数据库查询

PreparedStatement  sqlAddArtist=conexion.getConnection().prepareStatement("INSERT into artist values(?,?)");
        ResultSet resultado=sqlAddArtist.executeQuery();
        while(resultado.next()){
            sqlAddArtist.setString(1, artistaVO.getNombreArtista());
            sqlAddArtist.setInt(2, getMaxId()+1);
        }

这应该看起来像这样:

PreparedStatement  sqlAddArtist=conexion.getConnection().prepareStatement("INSERT into artist values(?,?)");
sqlAddArtist.setString(1, artistaVO.getNombreArtista());
sqlAddArtist.setInt(2, getMaxId()+1);
sqlAddArtist.execute();