public static ResultSet queryData(String sql) throws SQLException{ Connection connection = JDBC(); PreparedStatement ps = connection.prepareStatement(sql); ResultSet rs = ps.executeQuery(); return rs; }检查代码并修改

在代码中，虽然正确地获取了数据库连接，但没有关闭连接和释放资源，建议在finally块中关闭连接和释放资源。同时，建议使用try-with-resources语句自动关闭资源，代码修改如下：

public static ResultSet queryData(String sql) throws SQLException {
    try (Connection connection = JDBC();
         PreparedStatement ps = connection.prepareStatement(sql);
         ResultSet rs = ps.executeQuery()) {
        return rs;
    }
}

这样，当try语句块结束时，会自动关闭ResultSet、PreparedStatement和Connection对象，无需手动调用close()方法。

相关问题

package project; import java.sql.*; public class useOpea { public int query(String sql,Object[] objects) throws SQLException { int n=0; Connection conn=DriverManager.getConnection("jdbc:mysql://192.168.24.224:3306/dorm","root","123456"); PreparedStatement pstm=conn.prepareStatement(sql,1004,1007); if(objects!=null && objects.length>0){ for(int i=0;i<objects.length;i++ ) { pstm.setObject(i+1,objects[i]); } } ResultSet rs=pstm.executeQuery(); rs.last(); n=rs.getRow(); rs.close(); pstm.close(); conn.close(); return n; } public Object[][] queryToArray(String sql,Object[]pars) throws SQLException{ Connection conn=DriverManager.getConnection("jdbc:mysql://192.168.24.224:3306/dorm","root","123456"); PreparedStatement pstm=conn.prepareStatement(sql,1004,1007); if(pars!=null && pars.length>0){ for(int i=0;i<pars.length;i++ ) { pstm.setObject(i+1,pars[i]); } } ResultSet rs=pstm.executeQuery(); rs.last(); int n=rs.getRow(); ResultSetMetaData resultSetMetaData=rs.getMetaData(); int m=resultSetMetaData.getColumnCount(); Object[][]data=new Object[n][m]; rs.beforeFirst(); int i=0; while(rs.next()) { for(int j=0;j<m;j++) { data[i][j]=rs.getObject(j+1); i++; } } return data; } public static void main(String[]args) throws SQLException { useOpea userOpertion = new useOpea(); Object[][] data= userOpertion.queryToArray("select * from student", args); for(int i=0;i<data.length;i++) { for(int j=0;j<data[i].length;j++) { System.out.println(data[i][j]+" "); } } } }有什么错误

这段程序有一些潜在的问题，具体如下：

1. 在queryToArray方法中，如果查询结果集为空，即ResultSet.getRow()返回0，那么应该直接返回null，否则在后面的代码中会出现数组下标越界异常。

2. 在queryToArray方法中，内部循环的索引i应该累加在内层循环的末尾，否则会导致数据填充不完整。

3. 在main方法中，调用queryToArray方法时传入的参数args应该为null，否则会导致SQL语句解析错误。

4. 在main方法中，输出结果时应该使用print而不是println，否则会导致每个元素都换行输出。

综上所述，以下是修改后的程序代码：

package project;
import java.sql.*;

public class useOpea {
    public int query(String sql, Object[] objects) throws SQLException {
        int n = 0;
        Connection conn = DriverManager.getConnection("jdbc:mysql://192.168.24.224:3306/dorm", "root", "123456");
        PreparedStatement pstm = conn.prepareStatement(sql, 1004, 1007);
        if (objects != null && objects.length > 0) {
            for (int i = 0; i < objects.length; i++) {
                pstm.setObject(i + 1, objects[i]);
            }
        }
        ResultSet rs = pstm.executeQuery();
        rs.last();
        n = rs.getRow();
        rs.close();
        pstm.close();
        conn.close();
        return n;
    }

    public Object[][] queryToArray(String sql, Object[] pars) throws SQLException {
        Connection conn = DriverManager.getConnection("jdbc:mysql://192.168.24.224:3306/dorm", "root", "123456");
        PreparedStatement pstm = conn.prepareStatement(sql, 1004, 1007);
        if (pars != null && pars.length > 0) {
            for (int i = 0; i < pars.length; i++) {
                pstm.setObject(i + 1, pars[i]);
            }
        }
        ResultSet rs = pstm.executeQuery();
        rs.last();
        int n = rs.getRow();
        if (n == 0) {
            return null;
        }
        ResultSetMetaData resultSetMetaData = rs.getMetaData();
        int m = resultSetMetaData.getColumnCount();
        Object[][] data = new Object[n][m];
        rs.beforeFirst();
        int i = 0;
        while (rs.next()) {
            for (int j = 0; j < m; j++) {
                data[i][j] = rs.getObject(j + 1);
            }
            i++;
        }
        return data;
    }

    public static void main(String[] args) throws SQLException {
        useOpea userOpertion = new useOpea();
        Object[][] data = userOpertion.queryToArray("select * from student", null);
        if (data != null) {
            for (int i = 0; i < data.length; i++) {
                for (int j = 0; j < data[i].length; j++) {
                    System.out.print(data[i][j] + " ");
                }
                System.out.println();
            }
        }
    }
}

jdbc增删查改代码

以下是一个简单的JDBC增删查改的示例代码：

1. 建立数据库连接：

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class DatabaseConnection {
    private static final String URL = "jdbc:mysql://localhost:3306/mydatabase";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "password";

    public static Connection getConnection() throws SQLException {
        return DriverManager.getConnection(URL, USERNAME, PASSWORD);
    }
}

2. 添加数据：

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;

public class InsertData {
    public static void main(String[] args) {
        String sql = "INSERT INTO users (name, age) VALUES (?, ?)";
        try (Connection conn = DatabaseConnection.getConnection();
             PreparedStatement stmt = conn.prepareStatement(sql)) {
            stmt.setString(1, "John");
            stmt.setInt(2, 25);
            stmt.executeUpdate();
            System.out.println("Data inserted successfully.");
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

3. 删除数据：

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;

public class DeleteData {
    public static void main(String[] args) {
        String sql = "DELETE FROM users WHERE id = ?";
        try (Connection conn = DatabaseConnection.getConnection();
             PreparedStatement stmt = conn.prepareStatement(sql)) {
            stmt.setInt(1, 1);
            stmt.executeUpdate();
            System.out.println("Data deleted successfully.");
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

4. 修改数据：

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;

public class UpdateData {
    public static void main(String[] args) {
        String sql = "UPDATE users SET age = ? WHERE id = ?";
        try (Connection conn = DatabaseConnection.getConnection();
             PreparedStatement stmt = conn.prepareStatement(sql)) {
            stmt.setInt(1, 30);
            stmt.setInt(2, 1);
            stmt.executeUpdate();
            System.out.println("Data updated successfully.");
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

5. 查询数据：

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class QueryData {
    public static void main(String[] args) {
        String sql = "SELECT * FROM users";
        try (Connection conn = DatabaseConnection.getConnection();
             PreparedStatement stmt = conn.prepareStatement(sql);
             ResultSet rs = stmt.executeQuery()) {
            while (rs.next()) {
                int id = rs.getInt("id");
                String name = rs.getString("name");
                int age = rs.getInt("age");
                System.out.println("ID: " + id + ", Name: " + name + ", Age: " + age);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}