从数据库导出csv文件

从HeidiSQL 导数据出来成.csv文件

SELECT * FROM csv INTO OUTFILE 'C:\\feiniu\\note\\csv\\demo.csv' fields terminated by ','

CSV是什么

跟Excel表差不多

csv与excel对比：

• csv只能用于存储纯文本内容，excel不仅支持纯文本内容还支持二进制数据
• csv可以看做是excel的轻量级简单版实现，excel比csv更加强大
• csv文件可以被excel软件直接打开，csv文件一般用于表格数据的传输

纯文本形式存储表格数据，分隔字符有：逗号、分号 空格等

每行一条记录

关于操作csv文件

1. 读取CSV 文件转Java对象
2. CSV转Excel
3. CSV转对象后存数据库
4. 下载（导出）CSV文件

依赖：opencsv、easyexcel

导出Java对象转CSV导出文件

maven: OpenCSV

   <dependency>
            <groupId>com.opencsv</groupId>
            <artifactId>opencsv</artifactId>
            <version>5.6</version>
   </dependency>

controller

@RestController
@Slf4j
@RequestMapping("/file")
public class FileController extends BaseController{


    @Autowired
    private FileService fileService;

    @PostMapping("/downloadUserListCsv")
    public void downloadUserListCsv(HttpServletResponse response) {
        fileService.downUserListCsv(DownloadPublicUtil.UserListCsvHeader, response);
    }
}

service

@Service
public class FileServiceImpl implements FileService {
    @Override
    public void downUserListCsv(String[] head, HttpServletResponse response) {

        List<User> userList = List.of(
                User.builder().userId("1").userName("张三").sex("男").build(),
                User.builder().userId("2").userName("李四").sex("男").build(),
                User.builder().userId("3").userName("王五").sex("男").build()
        );

        ExportCsvUtils.exportCsv(head,userList,User.class,"user-list-1",response);
    }
}

utils

ExportCsvUtils

public class ExportCsvUtils {

    private ExportCsvUtils(){

    }

    public static <T> void exportCsv(String[] headers, List<T> list, Class c, String fileName, HttpServletResponse response){
        OutputStream outputStream = null;
        CSVWriter csvWriter = null;

        try {
            DownloadPublicUtil.setResponse(response, FileTypeEnum.CSV,
                    fileName, DownloadCharsetEnum.WINDOWS_1252);
            outputStream = response.getOutputStream();
//          prevent from turning Chinese into garbled code
            outputStream.write(0xEF);
            outputStream.write(0xBB);
            outputStream.write(0xBF);
       //     outputStream = response.getOutputStream();

            csvWriter = new CSVWriter(new OutputStreamWriter(outputStream, StandardCharsets.UTF_8));
            //写入标题行
            csvWriter.writeNext(headers);

            Map<String, String> map = new HashMap<>();
            Field[] declaredFields = c.getDeclaredFields();

            // each row
            for (T t : list) {
                for (Field declaredField : declaredFields){
                    declaredField.setAccessible(true);
                    Object o = null;

                    try {
                        o = declaredField.get(t);
                        if (o instanceof String){
                            // userId -> UserId
                            String fieldName = declaredField.getName();
                            String firstChar = fieldName.substring(0, 1).toUpperCase();
                            fieldName = firstChar + fieldName.substring(1);
                            map.put(fieldName,(String) o);
                        }
                    } catch (IllegalAccessException e) {
                        throw new RuntimeException(e);
                    }
                }
                ArrayList<String> values = new ArrayList<>();

                for(String header : headers){
                    //User Id -> UserId
                    header = header.replace(" ","");
                    String value = map.get(header);
                    values.add(value);
                }
                //  写入数据行
                csvWriter.writeNext(values.toArray(new String[0]));
                csvWriter.flush();
            }

        } catch (IOException e) {
            throw new RuntimeException(e);
        }finally {
                try {
                    if (csvWriter != null) {
                        csvWriter.close();
                    }
                    if (outputStream != null) {
                        outputStream.close();
                    }
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
        }
    }

DownloadPublicUtil

public class DownloadPublicUtil {

    public static String[] UserListCsvHeader =  {"User Id","User Name","Sex"};

    private DownloadPublicUtil(){

    }

    public static void setResponse(HttpServletResponse response, FileTypeEnum fileTypeEnum, String fileName, DownloadCharsetEnum charsets) {
        fileName = URLEncoder.encode(fileName, StandardCharsets.UTF_8).replaceAll("\\+", "%20");
        response.reset();
        response.setCharacterEncoding(charsets.getVal());
        if (fileTypeEnum.equals(FileTypeEnum.CSV)) {
            response.setContentType("text/" + fileTypeEnum + ";charset=" + charsets.getVal());
        } else {
            response.setContentType("application/" + fileTypeEnum + ";charset=" + charsets.getVal());
        }
        response.setHeader("Content-Disposition", "attachment; filename=" + fileName + fileTypeEnum.getSuffix());
    }
}

enum

@Getter
@AllArgsConstructor
public enum DownloadCharsetEnum {

    UTF_8("utf-8"),
    WINDOWS_1252("windows-1252");

    private final String val;
}

@Getter
public enum FileTypeEnum {
    EXCEL(".xlsx"),
    PDF(".pdf"),
    CSV(".csv");

    private final String suffix;

    FileTypeEnum(String suffix) {
        this.suffix = suffix;
    }
}

没设置response