java - 用数据库值填充数组列表

Question

/*
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 * and open the template in the editor.
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package XawalaManager;

import java.sql.*; // DB handling package
import java.util.*;
import javax.swing.table.*;
import javax.swing.table.AbstractTableModel;
import java.awt.*;
import javax.swing.*;
import javax.swing.event.TableModelEvent;

/**
 *
 * @author Abdi Aden
 */
public class DBHandler extends AbstractTableModel {


    private static Connection connection;

    private static Statement stmt;
    Vector columnHeaders;
    Vector tableData;
    static int id;
   public static int autokey = -1;
    static String [] contactList;
    static  ArrayList senders =  new ArrayList();

    public DBHandler() {
        Vector rowData;
        try {
            Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
            // Assumes Messages.mdb is in the same folder as MessageData.class
            String sourceURL = "jdbc:odbc:Driver={Microsoft Access Driver (*.mdb)};DBQ=olympic.mdb;";
            connection = DriverManager.getConnection(sourceURL, "admin", "");
            stmt = connection.createStatement();           
            String sql = "Select * FROM senderTable";
            Statement stmt = connection.createStatement();
            ResultSet rs = stmt.executeQuery(sql);
            ResultSetMetaData md = rs.getMetaData();

            int count = md.getColumnCount();
            columnHeaders = new Vector(count);
           tableData = new Vector();
            for (int i = 1; i <= count; i++) {
                columnHeaders.addElement(md.getColumnName(i));
            }
            while (rs.next()) {
                rowData = new Vector(count);
                for (int i = 1; i <= count; i++) {
                    rowData.addElement(rs.getObject(i));
                }
               tableData.addElement(rowData);
            }


        } catch (Exception e) {
            System.out.println("There is an connection error:  " +e );
        }
    }

    public int getColumnCount() {
        return columnHeaders.size();
    }

    public int getRowCount() {
        return tableData.size();
    }

    public Object getValueAt(int row, int column) {
        Vector rowData = (Vector) (tableData.elementAt(row));
        return rowData.elementAt(column);
    }



    public boolean isCellEditable(int row, int column) {
        return false;
    }

    public String getColumnName(int column) {
        return (String) (columnHeaders.elementAt(column));
    }






    public static ArrayList getSend(){

        try{
            ResultSet res = stmt.executeQuery("SELECT * FROM senderTable");
            //ArrayList senders =  new ArrayList();
            while (res.next()){
                String send = res.getString(2);
                senders.add(send);

            }
        }catch (Exception e ){
            System.out.println("getSend "+e);
            return null;
        }
        return senders;
    }

    // close the database

    public static void close() {
        try {
            connection.close();
        } catch (Exception e) {
            // this shouldn't happen
            System.out.println("close"+e);
        }
    }
}

这是我的完整代码，我的表模型单词很好地填满了我的表，但数组未满，并给了我一个堆栈跟踪:

getSend java.lang.NullPointerException
Exception in thread "main" java.lang.NullPointerException
        at XawalaManager.mainView.<init>(mainView.java:86)
        at XawalaManager.XawalaManager.<init>(XawalaManager.java:40)
        at XawalaManager.XawalaManager.main(XawalaManager.java:108)
Java Result: 1

像这样

Answer 1

注释掉这一行:

//ArrayList senders =  new ArrayList();

<小时/>

将类型更改为 List 并使用泛型

List<String> senders =  new ArrayList<String>();

<小时/>

添加以下行:(DBUrl 是您的数据库地址)

Connection conn = null;
Statement  stmt = null;
conn = DriverManager.getConnection("DBUrl");
stmt = con.createStatement();

<小时/>

这是您修改后的代码:

public static ArrayList getSend(){

  Connection conn = null;
  Statement  stmt = null;
  ResultSet res = null;
  List<String> senders =  new ArrayList<String>();

  try{
    conn = DriverManager.getConnection("DBUrl");
    stmt = con.createStatement();
    res = stmt.executeQuery("SELECT * FROM senderTable");

    while (res.next()){
        String send = res.getString(2);
        senders.add(send);

    }
  }catch (Exception e ){
    System.out.println("getSend "+e);
    return null;
  }
 return senders;
}

如果您需要更多帮助，只需发布​​异常的堆栈跟踪即可。

编辑:我的本地电脑上没有数据库驱动程序和环境，但以下代码应该可以工作。

import java.sql.*;
import java.util.*;
import javax.swing.table.AbstractTableModel;

public class DBHandler extends AbstractTableModel {

    private static Connection connection;
    private static Statement stmt;
    List<String> columnHeaders;
    List<List<String>> tableData;
    static int id;
    public static int autokey = -1;
    static String[] contactList;
    static ArrayList<String> senders = new ArrayList<String>();

    public DBHandler() {
        List rowData = null;
        try {
            Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
            String sourceURL = "jdbc:odbc:Driver={Microsoft Access Driver (*.mdb)};DBQ=olympic.mdb;";
            connection = DriverManager.getConnection(sourceURL, "admin", "");
            stmt = connection.createStatement();
            String sql = "Select * FROM senderTable";
            ResultSet rs = stmt.executeQuery(sql);
            ResultSetMetaData md = rs.getMetaData();

            int count = md.getColumnCount();
            columnHeaders = new ArrayList<String>();
            tableData = new ArrayList<List<String>>();
            for (int i = 1; i <= count; i++) {
                columnHeaders.add(md.getColumnName(i));
            }
            while (rs.next()) {
                rowData = new ArrayList<String>();
                for (int i = 1; i <= count; i++) {
                    rowData.add(rs.getObject(i));
                }
                tableData.add(rowData);
            }


        } catch (Exception e) {
            System.out.println("There is an connection error:  " + e);
        }
    }

    public int getColumnCount() {
        return columnHeaders.size();
    }

    public int getRowCount() {
        return tableData.size();
    }

    public Object getValueAt(int row, int column) {
        ArrayList rowData = (ArrayList) (tableData.get(row));
        return rowData.get(column);
    }

    @Override
    public boolean isCellEditable(int row, int column) {
        return false;
    }

    @Override
    public String getColumnName(int column) {
        return (String) (columnHeaders.get(column));
    }

    public static ArrayList getSend() {

        try {
            ResultSet res = stmt.executeQuery("SELECT * FROM senderTable");
            while (res.next()) {
                String send = res.getString(2);
                senders.add(send);
            }
        } catch (Exception e) {
            System.out.println("getSend " + e);
            return null;
        }
        return senders;
    }

    public static void close() {
        try {
            connection.close();
        } catch (Exception e) {
            System.out.println("close" + e);
        }
    }
}