如何使用Java编程语言通过FTP来实现文件的上传、下载、查找和删除功能？

使用Java编程语言通过FTP来实现文件的上传、下载、查找和删除功能，通常会依赖于像Apache Commons Net这样的FTP库。这里是一个简要的示例：

### 1. **文件上传（PUT）：**

import org.apache.commons.net.ftp.FTPClient;

public void uploadFile(String server, String user, String pass, String filePath, String remotePath) throws IOException {
    FTPClient client = new FTPClient();
    client.connect(server);
    client.login(user, pass);
    client.changeWorkingDirectory(remotePath); // 如果需要先切换到目标目录

    FileInputStream fis = new FileInputStream(filePath);
    boolean result = client.storeFile(new File(remotePath).getName(), fis);
    if (result) {
        System.out.println("文件 " + filePath + " 上传成功");
    } else {
        System.out.println("文件上传失败");
    }
    client.logout();
    client.disconnect();
}

### 2. **文件下载（GET）：**

import org.apache.commons.net.ftp.FTPClient;

public void downloadFile(String server, String user, String pass, String remotePath, String localPath) throws IOException {
    FTPClient client = new FTPClient();
    client.connect(server);
    client.login(user, pass);
    client.changeWorkingDirectory("/"); // 如果需要先回到根目录

    InputStream fis = client.retrieveFileStream(remotePath);
    FileOutputStream fos = new FileOutputStream(localPath);
    byte[] buffer = new byte[1024];
    while (true) {
        int bytesRead = fis.read(buffer);
        if (bytesRead == -1) break; // 文件读取完成
        fos.write(buffer, 0, bytesRead);
    }
    fis.close();
    fos.close();

    System.out.println("文件 " + remotePath + " 下载到本地 " + localPath);
    client.logout();
    client.disconnect();
}

### 3. **文件查找（LIST）：**

import org.apache.commons.net.ftp.FTPClient;

public void listFiles(String server, String user, String pass) throws IOException {
    FTPClient client = new FTPClient();
    client.connect(server);
    client.login(user, pass);

    String[] files = client.listFiles("/");
    for (String fileName : files) {
        System.out.println(fileName);
    }
    client.logout();
    client.disconnect();
}

### 4. **文件删除（DELETE）：**

import org.apache.commons.net.ftp.FTPClient;

public void deleteFile(String server, String user, String pass, String remotePath) throws IOException {
    FTPClient client = new FTPClient();
    client.connect(server);
    client.login(user, pass);

    boolean success = client.deleteFile(remotePath);
    if (success) {
        System.out.println("文件 " + remotePath + " 删除成功");
    } else {
        System.out.println("文件删除失败");
    }
    client.logout();
    client.disconnect();
}

以上代码需注意异常处理，并根据实际需求进行适当调整。