Java+Swing: 从数据库中查询数据并显示在表格中整理11-编程知识

分析：要想从数据库中查询数据并分页展示到表格中，我觉得应该按照这个思路：首先就是发起请求，此时需要向数据库中传递三个参数：当前页码（pageNum）、每一页的数量（pageSize）、搜索的关键词（searchKey）、控制从第几页开始（startPageNum）

然后就是接受返回的结果：数据（data）、 总数据条数（totalCount）

1. 首先在MainView中定义两个变量，给出初始值

    // 分页：定义两个变量private int pageNum = 1;  // 当前是第几页private int pageSize = 10; // 一页显示多少条数据

2. 创建请求的类对象

package com.resquest;import lombok.Data;/*** @Author：xiexu* @Date：2023/12/12 12:59*/
@Data
public class StudentRequest {private int pageNum;private int pageSize;private String searchKey;   //  搜索关键字private int startPageNum;  // 控制从第几页开始public int getStartPageNum() {return (pageNum - 1) * pageSize;}public void setStartPageNum(int startPageNum) {this.startPageNum = startPageNum;}
}

3. 创建接受返回结果的类对象

package com.response;import lombok.Data;import java.util.Vector;/*** @Author：xiexu* @Date：2023/12/12 13:07*/
@Data
public class TableDTO {private Vector<Vector<Object>> data;private int totalCount;
}

4. 定义接口

返回的结果是TableDTO类型

public interface StudentService {TableDTO queryStudent(StudentRequest studentRequest);
}

5. 实现接口

package com.service.Impl;import com.response.TableDTO;
import com.resquest.StudentRequest;
import com.service.StudentService;
import com.utils.DBUtil;import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Vector;/*** @Author：xiexu* @Date：2023/12/11 10:40*/
public class StudentServiceImpl implements StudentService {@Overridepublic TableDTO queryStudent(StudentRequest studentRequest){StringBuilder sql = new StringBuilder();sql.append("select * from detail ");if (studentRequest.getSearchKey() != null && !"".equals(studentRequest.getSearchKey().trim())) {sql.append(" where name like '%"+ studentRequest.getSearchKey() + "%'");}sql.append("order by id desc limit ").append(studentRequest.getStartPageNum()).append(",").append(studentRequest.getPageSize());// 执行Connection connection = null;PreparedStatement preparedStatement = null;ResultSet resultSet = null;TableDTO tableDTO = new TableDTO(); // 返回的数据try {connection = DBUtil.getConnection();preparedStatement = connection.prepareStatement(sql.toString());resultSet = preparedStatement.executeQuery();  // 执行查询返回结果集// 查询记录Vector<Vector<Object>> queryDatas = fillTableData(resultSet);tableDTO.setData(queryDatas);sql.setLength(0);sql.append("select count(*) from detail ");if (studentRequest.getSearchKey() != null && !"".equals(studentRequest.getSearchKey().trim())) {sql.append(" where name like '%"+ studentRequest.getSearchKey() + "%'");}preparedStatement = connection.prepareStatement(sql.toString());resultSet = preparedStatement.executeQuery();while (resultSet.next()) {int count = resultSet.getInt(1);tableDTO.setTotalCount(count);}return tableDTO;}catch (Exception e) {e.printStackTrace();} finally {DBUtil.closeRS(resultSet);DBUtil.closePS(preparedStatement);DBUtil.closeConnection(connection);}return null;}private static Vector<Vector<Object>> fillTableData(ResultSet resultSet) throws SQLException {Vector<Vector<Object>> data = new Vector<>();while (resultSet.next()) {// 遍历查询的每一条记录Vector<Object> oneRecord = new Vector<>();int id = resultSet.getInt("id");String name = resultSet.getString("name");String no = resultSet.getString("no");String homeTown = resultSet.getString("homeTown");int chinese = resultSet.getInt("chinese");int math = resultSet.getInt("math");int english = resultSet.getInt("english");int total = resultSet.getInt("total");oneRecord.addElement(id);oneRecord.addElement(name);oneRecord.addElement(no);oneRecord.addElement(homeTown);oneRecord.addElement(chinese);oneRecord.addElement(math);oneRecord.addElement(english);oneRecord.addElement(total);data.addElement(oneRecord);}return data;}
}

上述代码详细解释：

1. 下方代码主要是编写sql语句的，使用StringBuilder()动态构建字符串。首先判断searchKey是否为空或是否为空字符串，false的话，就直接下方的sql语句，如果为true的话，需要按照name进行模糊查询，然后再拼接下方的sql语句

        StringBuilder sql = new StringBuilder();sql.append("select * from detail ");if (studentRequest.getSearchKey() != null && !"".equals(studentRequest.getSearchKey().trim())) {sql.append(" where name like '%"+ studentRequest.getSearchKey() + "%'");}sql.append("order by id desc limit ").append(studentRequest.getStartPageNum()).append(",").append(studentRequest.getPageSize());

2. 查询数据，并注入到tableDTO中

// 查询记录Vector<Vector<Object>> queryDatas = fillTableData(resultSet);tableDTO.setData(queryDatas);

fillTableData函数：

private static Vector<Vector<Object>> fillTableData(ResultSet resultSet) throws SQLException {Vector<Vector<Object>> data = new Vector<>();while (resultSet.next()) {// 遍历查询的每一条记录Vector<Object> oneRecord = new Vector<>();int id = resultSet.getInt("id");String name = resultSet.getString("name");String no = resultSet.getString("no");String homeTown = resultSet.getString("homeTown");int chinese = resultSet.getInt("chinese");int math = resultSet.getInt("math");int english = resultSet.getInt("english");int total = resultSet.getInt("total");oneRecord.addElement(id);oneRecord.addElement(name);oneRecord.addElement(no);oneRecord.addElement(homeTown);oneRecord.addElement(chinese);oneRecord.addElement(math);oneRecord.addElement(english);oneRecord.addElement(total);data.addElement(oneRecord);}return data;}

3. 查询数据数量

            sql.setLength(0);  // 首先将之前的sql语句置为空sql.append("select count(*) from detail ");if (studentRequest.getSearchKey() != null && !"".equals(studentRequest.getSearchKey().trim())) {sql.append(" where name like '%"+ studentRequest.getSearchKey() + "%'");}preparedStatement = connection.prepareStatement(sql.toString());resultSet = preparedStatement.executeQuery();while (resultSet.next()) {int count = resultSet.getInt(1);tableDTO.setTotalCount(count);}

4. MainView中使用

        StudentServiceImpl studentService = new StudentServiceImpl();StudentRequest studentRequest = new StudentRequest();studentRequest.setPageNum(pageNum);studentRequest.setPageSize(pageSize);studentRequest.setSearchKey(searchTxt.getText().trim());TableDTO tableDTO = studentService.queryStudent(studentRequest);Vector<Vector<Object>> data = tableDTO.getData();int totalCount = tableDTO.getTotalCount();