在循环中以 CSV 格式获取结果

Question

我想打印从 JDBC 连接获得的结果集，并希望它在 aloop 中打印每个结果集。所以我的代码如下：

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.PrintWriter;

import java.sql.*;
import java.util.*;

public class zone {

    List<model> listOfBlogs;

    public zone() {
        Connection conn = null;
        listOfBlogs = new ArrayList<model>();

        // connect to the database

        conn = connectToDatabaseOrDie();

        // get the data
        populateListOfTopics(conn, listOfBlogs);

        //print the data
        printTopics(listOfBlogs);
    }

    public List<model> printTopics(List<model> listOfBlogs) {
        Iterator<model> it = listOfBlogs.iterator();
        while (it.hasNext()) {
            model blog = (model) it.next();
            System.out.println(blog.day + "  " + blog.hour + " " + blog.zone_id);
        }
        return listOfBlogs;
    }

    private void populateListOfTopics(Connection conn, List<model> listOfBlogs) {
        try {
            for (int j = 9; j < 10; j++) {
                for (int i = 10; i < 12; i++) {

                    String sql = "SELECT day,hour,zone_id FROM public.zone_block_table where day=? and hour=?";
                    PreparedStatement pstmt = conn.prepareStatement(sql);
                    pstmt.setInt(1, j);
                    pstmt.setInt(2, i);

                    ResultSet rs = pstmt.executeQuery();

                    while (rs.next()) {
                        model blog = new model();

                        blog.day = rs.getInt("day");
                        blog.hour = rs.getInt("hour");
                        blog.zone_id = rs.getInt("zone_id");

                        listOfBlogs.add(blog);
                    }
                    convertToCsv(rs, i, j);

                    rs.close();
                    pstmt.close();
                }
            }
        } catch (SQLException se) {
            System.err.println("Threw a SQLException creating the list of state.");
            System.err.println(se.getMessage());
        } catch (Exception e) {
            System.out.println("Err");
            e.printStackTrace();
        }
    }

    private Connection connectToDatabaseOrDie() {
        Connection conn = null;
        try {
            Class.forName("org.postgresql.Driver");
            String url = "jdbc:postgresql://localhost:5432/mvc_data_base";
            conn = DriverManager.getConnection(url, "postgres", "122333");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return conn;
    }

    public void convertToCsv(ResultSet rs, int k, int l) throws SQLException, FileNotFoundException {
        PrintWriter csvWriter = new PrintWriter(new File("state_" + k + "_" + l + ".csv"));
        ResultSetMetaData meta = rs.getMetaData();
        int numberOfColumns = meta.getColumnCount();
        String dataHeaders = "\"" + meta.getColumnName(1) + "\"";
        for (int i = 2; i < numberOfColumns + 1; i++) {
            dataHeaders += ",\"" + meta.getColumnName(i) + "\"";
        }
        csvWriter.println(dataHeaders);
        while (rs.next()) {
            String row = "\"" + rs.getString(1) + "\"";
            for (int i = 2; i < numberOfColumns + 1; i++) {
                row += ",\"" + rs.getString(i) + "\"";
            }
            csvWriter.println(row);
        }
        csvWriter.close();
    }
}

但结果集打印完美。但我找不到任何目的地生成的任何 csv 文件。感谢任何帮助。

Answer 1

有一种直接方法可以使用 opencsv 从结果集中创建 CSV 文件。试试看

CSVWriter writer = new CSVWriter(new FileWriter(csvtemp), ',' ,CSVWriter.NO_QUOTE_CHARACTER , CSVWriter.NO_ESCAPE_CHARACTER , "\r\n");

writer.writeAll(myResultSet, true);
writer.close();