字段和属性的意思，static的作用，static string path;这句代码中static的所用

在面向对象编程中，一个类包含了类名和数据（字段）以及方法（属性），其中字段是指一个类中的变量，属性是指与变量相关联的方法。字段用于存储对象的状态信息，而属性则用于控制对象状态的访问方式。

static是C++中的一个关键字，表示静态的、不变的，使用static修饰的成员变量和成员函数属于整个类，而不是属于类的某个对象。当static修饰成员变量时，该变量被所有类的对象所共享，而不是每个对象都拥有一份独立的拷贝；当static修饰成员函数时，该函数可以直接通过类名调用，无需创建对象，因为它不需要访问任何特定对象的状态。

在代码中，static string path;表示在类中定义了一个静态的字符串变量path，该变量被所有类的对象所共享，可以通过类名直接访问。这样做的好处是可以在不创建对象的情况下访问和修改该变量，从而节省内存空间。

相关问题

<h1>上传/下载文件</h1> <form method="post" action="/file/upload" enctype="multipart/form-data"> <input type="file" name="file" id="fileInput"/> <input type="submit" value="上传" /> </form> <hr> <form method="post" action="/file/download" > <input type="text" name="fileName" placeholder="请输入文件名" /> <input type="submit" value="下载" id="downloadBtn" /> </form> public class SFTPUtil { private static final String host = "10.60.0.160"; private static final int port = 22; private static final String username = "root"; private static final String password = "Z20"; private static Session session = null; public static void connect() throws Exception { } public static void upload(MultipartFile file, String path, String fileName) throws Exception { } public static boolean download(HttpServletResponse response, String path, String fileName) throws Exception { } @Controller @RequestMapping("/file") public class FileController { private static final String UPLOAD_PATH = "/data/sftp/adtuser1/upload/winbidding/"; private static final String DOWNLOAD_PATH = "/data/sftp/adtuser1/upload/winbidding/"; @PostMapping("/upload") @ResponseBody public ModelAndView upload(@RequestParam("file") MultipartFile file) { } @PostMapping("/download") public ModelAndView download(@RequestParam("fileName") String fileName, HttpServletResponse response) throws Exception { } 数据库有host port username password UPLOAD_PATH DOWNLOAD_PATH csmc字段，把上边写死的改成数据库查询，前台页面增加csmc字段下拉框，根据csmc字段把查出来的配置数据完成上传下载功能，用的mysql数据库，把代码改好写出来

首先需要在数据库中创建一个表，用于存储SFTP连接的相关信息：

CREATE TABLE sftp_config (
  id INT PRIMARY KEY AUTO_INCREMENT,
  csmc VARCHAR(50),
  host VARCHAR(50),
  port INT,
  username VARCHAR(50),
  password VARCHAR(50),
  upload_path VARCHAR(255),
  download_path VARCHAR(255)
);

然后在Spring Boot项目中创建一个SFTPUtil类，用于实现SFTP上传和下载功能：

import com.jcraft.jsch.*;

import org.springframework.web.multipart.MultipartFile;

import java.io.*;
import java.util.Properties;

public class SFTPUtil {

    private String host;
    private int port;
    private String username;
    private String password;
    private String uploadPath;
    private String downloadPath;
    private Session session;

    public SFTPUtil(String host, int port, String username, String password, String uploadPath, String downloadPath) {
        this.host = host;
        this.port = port;
        this.username = username;
        this.password = password;
        this.uploadPath = uploadPath;
        this.downloadPath = downloadPath;
    }

    public void connect() throws Exception {
        JSch jsch = new JSch();
        session = jsch.getSession(username, host, port);
        session.setPassword(password);
        Properties config = new Properties();
        config.put("StrictHostKeyChecking", "no");
        session.setConfig(config);
        session.connect();
    }

    public void upload(MultipartFile file, String fileName) throws Exception {
        ChannelSftp channel = (ChannelSftp) session.openChannel("sftp");
        channel.connect();
        channel.cd(uploadPath);
        InputStream inputStream = file.getInputStream();
        channel.put(inputStream, fileName);
        inputStream.close();
        channel.disconnect();
    }

    public boolean download(HttpServletResponse response, String fileName) throws Exception {
        ChannelSftp channel = (ChannelSftp) session.openChannel("sftp");
        channel.connect();
        channel.cd(downloadPath);
        SftpATTRS attrs = channel.lstat(fileName);
        if (attrs == null) {
            channel.disconnect();
            return false;
        }
        response.setHeader("Content-Disposition", "attachment; filename=\"" + fileName + "\"");
        OutputStream outputStream = response.getOutputStream();
        channel.get(fileName, outputStream);
        outputStream.flush();
        outputStream.close();
        channel.disconnect();
        return true;
    }

}

然后在Spring Boot项目中创建一个FileController类，用于处理文件上传和下载请求：

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.multipart.MultipartFile;

import javax.servlet.http.HttpServletResponse;
import java.util.List;
import java.util.Map;

@Controller
@RequestMapping("/file")
public class FileController {

    @Autowired
    private JdbcTemplate jdbcTemplate;

    @PostMapping("/upload")
    @ResponseBody
    public String upload(@RequestParam("file") MultipartFile file, @RequestParam("csmc") String csmc) {
        try {
            // 从数据库中获取SFTP连接配置信息
            String sql = "SELECT * FROM sftp_config WHERE csmc = ?";
            Map<String, Object> map = jdbcTemplate.queryForMap(sql, csmc);
            String host = (String) map.get("host");
            int port = (int) map.get("port");
            String username = (String) map.get("username");
            String password = (String) map.get("password");
            String uploadPath = (String) map.get("upload_path");
            String fileName = file.getOriginalFilename();

            // 使用SFTP上传文件
            SFTPUtil sftpUtil = new SFTPUtil(host, port, username, password, uploadPath, null);
            sftpUtil.connect();
            sftpUtil.upload(file, fileName);

            return "上传成功";
        } catch (Exception e) {
            e.printStackTrace();
            return "上传失败";
        }
    }

    @PostMapping("/download")
    public void download(@RequestParam("fileName") String fileName, @RequestParam("csmc") String csmc, HttpServletResponse response) throws Exception {
        // 从数据库中获取SFTP连接配置信息
        String sql = "SELECT * FROM sftp_config WHERE csmc = ?";
        Map<String, Object> map = jdbcTemplate.queryForMap(sql, csmc);
        String host = (String) map.get("host");
        int port = (int) map.get("port");
        String username = (String) map.get("username");
        String password = (String) map.get("password");
        String downloadPath = (String) map.get("download_path");

        // 使用SFTP下载文件
        SFTPUtil sftpUtil = new SFTPUtil(host, port, username, password, null, downloadPath);
        sftpUtil.connect();
        boolean result = sftpUtil.download(response, fileName);
        if (!result) {
            response.getWriter().write("文件不存在");
        }
    }

    @GetMapping("/csmcList")
    @ResponseBody
    public List<String> getCsmcList() {
        // 从数据库中获取所有的csmc字段
        String sql = "SELECT DISTINCT csmc FROM sftp_config";
        List<String> csmcList = jdbcTemplate.queryForList(sql, String.class);
        return csmcList;
    }

}

最后，在HTML页面中加入下面的代码，即可实现文件上传和下载：

<h1>上传/下载文件</h1>
<form method="post" action="/file/upload" enctype="multipart/form-data">
    <input type="file" name="file" id="fileInput"/>
    <select name="csmc" id="csmcSelect"></select>
    <input type="submit" value="上传"/>
</form>
<hr>
<form method="post" action="/file/download">
    <input type="text" name="fileName" placeholder="请输入文件名"/>
    <select name="csmc" id="csmcSelect"></select>
    <input type="submit" value="下载" id="downloadBtn"/>
</form>
<script>
    // 获取csmc列表
    $.get("/file/csmcList", function (data) {
        var csmcSelect = $("#csmcSelect");
        for (var i = 0; i < data.length; i++) {
            var option = $("<option>").val(data[i]).text(data[i]);
            csmcSelect.append(option);
        }
    });
</script>

涉及到CredentialCache的代码是： internal class ErrorStationHandler { private static readonly string FILE_PATH = @"\\111.11.111.11\共享\error_station\error_stations.txt"; private static readonly string FILE_ZD = @"\111.11.111.11\共享\error_station\fileZD.txt"; private readonly Dictionary<string, int> stationErrorTypes = new Dictionary<string, int>(); private readonly StringBuilder sb = new StringBuilder(); private readonly CredentialCache _cache; public ErrorStationHandler(CredentialCache cache) { _cache = cache; stationErrorTypes = LoadDictionary(FILE_ZD); }

根据您提供的代码，`ErrorStationHandler` 类的构造函数接受一个 `CredentialCache` 类型的参数，并将其赋值给私有字段 `_cache`。在代码中，构造函数还调用了 `LoadDictionary` 方法来加载错误类型字典。

如果您想要使用 `ErrorStationHandler` 类的实例来调用 `WriteErrorStationsToTxt` 方法，您需要修改代码以创建 `ErrorStationHandler` 对象的实例，并将 `CredentialCache` 对象作为参数传递给构造函数。

以下是一个示例：

CredentialCache cache = new CredentialCache();
// 根据需要设置 cache 的属性

ErrorStationHandler errorStationHandler = new ErrorStationHandler(cache);
errorStationHandler.WriteErrorStationsToTxt(tyMonitors);

请确保在使用 `WriteErrorStationsToTxt` 方法之前创建了 `ErrorStationHandler` 对象，并将正确的 `CredentialCache` 对象传递给构造函数。

如果还有其他问题，请提供更多关于代码结构和上下文的信息，以便我可以提供更具体的帮助。