NUHMAN.com

📌 Problem

You need to connect to and manage multiple SFTP servers in Java using the JSch library, where each server uses private key authentication (with or without a passphrase). You also want to perform file operations on each server during the same program execution.

🚀 Solution Overview

We'll use the JSch (Java Secure Channel) library to:

1. Load the appropriate private key.
2. Establish SFTP sessions per server.
3. Perform SFTP file operations.
4. Cleanly disconnect after use.

📦 Step 1: Add the JSch Dependency

If you're using Maven, add this to your pom.xml:

xml

<dependency>
    <groupId>com.jcraft</groupId>
    <artifactId>jsch</artifactId>
    <version>0.1.55</version>
</dependency>

🧑‍💻 Step 2: Java Code to Handle Multiple SFTP Servers

java

import com.jcraft.jsch.ChannelSftp;
import com.jcraft.jsch.JSch;
import com.jcraft.jsch.Session;
import java.util.Properties;

public class SFTPManager {

    // ✅ Connect to a single SFTP server using a private key
    public static ChannelSftp connectToSFTP(String username, String host, int port, String privateKeyPath, String passphrase) throws Exception {
        JSch jsch = new JSch();
        jsch.addIdentity(privateKeyPath, passphrase); // null if no passphrase

        Session session = jsch.getSession(username, host, port);

        // 🔒 Bypass host key confirmation for simplicity
        Properties config = new Properties();
        config.put("StrictHostKeyChecking", "no");
        session.setConfig(config);

        session.connect();

        // 📡 Open and return SFTP channel
        ChannelSftp channel = (ChannelSftp) session.openChannel("sftp");
        channel.connect();
        return channel;
    }

    public static void main(String[] args) {
        try {
            // 📜 Define details for multiple SFTP servers
            String[][] sftpServers = {
                {"username1", "host1.example.com", "22", "/path/to/privateKey1", "passphrase1"},
                {"username2", "host2.example.com", "22", "/path/to/privateKey2", "passphrase2"}
            };

            // 🔁 Loop through each server and perform operations
            for (String[] server : sftpServers) {
                String username = server[0];
                String host = server[1];
                int port = Integer.parseInt(server[2]);
                String privateKeyPath = server[3];
                String passphrase = server[4];

                ChannelSftp sftp = connectToSFTP(username, host, port, privateKeyPath, passphrase);

                System.out.println("✅ Connected to " + host);

                // 📂 Perform your file operations here
                // Example: sftp.put("/local/file.txt", "/remote/dir/file.txt");

                // ❌ Disconnect cleanly
                sftp.disconnect();
                sftp.getSession().disconnect();
                System.out.println("🔌 Disconnected from " + host);
            }

        } catch (Exception e) {
            System.err.println("❗ Error connecting to SFTP server: " + e.getMessage());
            e.printStackTrace();
        }
    }
}

🧪 Example Output

css

✅ Connected to host1.example.com
🔌 Disconnected from host1.example.com
✅ Connected to host2.example.com
🔌 Disconnected from host2.example.com

🔍 Key Concepts

ConceptPurposejsch.addIdentity(path, passphrase)Loads the private key for authenticationsession.setConfig(...)Skips manual key verification (not for production without security checks)channelSftp.put(...)Upload file (can also use get, ls, cd, etc.)loop through server configsScales the solution to manage many servers

🛡️ Security Notes

• ✅ Use proper key permissions (chmod 600 for PEM files).
• 🔐 Avoid setting "StrictHostKeyChecking" to "no" in production—use known_hosts.
• 🧾 Consider logging errors and successes per host.

🔁 Possible Enhancements

• Store server configs in a JSON or .properties file.
• Wrap SFTP operations into a utility/service class.
• Add retry logic and timeout handling.
• Use connection pooling for frequent use.