一种多传输协议，相当于加密版的FTP。当你在FTP服务器上收发文件的时候，你面临两个风险。第一个风险是在上载文件的时候为文件加密。第二个风险是，这些文件在你等待接收方下载的时候将停留在FTP服务器上，这时你如何保证这些文件的安全。你的第二个选择(创建一个支持SSL的FTP服务器)能够让你的主机使用一个FTPS连接上载这些文件。这包括使用一个在FTP协议下面的SSL层加密控制和数据通道。一种替代FTPS的协议是安全文件传输协议(SFTP)。这个协议使用SSH文件传输协议加密从客户机到服务器的FTP连接。
FTPS是在安全套接层使用标准的FTP协议和指令的一种增强型FTP协议，为FTP协议和数据通道增加了SSL安全功能。FTPS也称作“FTP-SSL”和“FTP-over-SSL”。SSL是一个在客户机和具有SSL功能的服务器之间的安全连接中对数据进行加密和解密的协议。

当使用FTPS与服务器连接时，有两种方法：显式和隐式。
简单来说：
显示又叫FTPES, FTPS客户端跟FTPS服务器必须显式使用一种同样的加密方法。如果客户端不要求加密，服务器也允许非加密通讯。
隐式 就是客户端直接通过TSL/SSL加密与服务器联系，如果服务器无响应，则停止通讯。

FTP4J 支持 FTPS/FTPES secured connection，其中使用FTPES还是原来的21端口，使用FTPS使用的是990端口，使用SFTP的是22端口，以下说的不包含SFTP内容。

可以查看Serv-U域详细信息查看服务邦定的端口，默认情况下是以下内容：

如果我们使用flashfxp进行连接，则使用不同连接方式时要进行选择，普通FTP连接使用21端口，不用选择：

我们通过21端口进行显示FTPS连接：

Java代码

1. package test;
2. import it.sauronsoftware.ftp4j.FTPClient;
3. import java.security.SecureRandom;
4. import java.security.cert.X509Certificate;
5. import javax.net.ssl.SSLContext;
6. import javax.net.ssl.SSLSocketFactory;
7. import javax.net.ssl.TrustManager;
8. import javax.net.ssl.X509TrustManager;
9. /**
10. * 通过21端口进行显示FTPS连接
11. * @说明
12. * @author cuisuqiang
13. * @version 1.0
14. * @since
15. */
16. public class Ftp4jTest {
17. public static void main(String[] args) {
18. try {
19. TrustManager[] trustManager = new TrustManager[] { new X509TrustManager() {
20. public X509Certificate[] getAcceptedIssuers() {
21. return null;
22. }
23. public void checkClientTrusted(X509Certificate[] certs,
24. String authType) {
25. }
26. public void checkServerTrusted(X509Certificate[] certs,
27. String authType) {
28. }
29. } };
30. SSLContext sslContext = null;
31. sslContext = SSLContext.getInstance("SSL");
32. sslContext.init(null, trustManager, new SecureRandom());
33. SSLSocketFactory sslSocketFactory = sslContext.getSocketFactory();
34. FTPClient client = new FTPClient();
35. client.setSSLSocketFactory(sslSocketFactory);
36. client.setSecurity(FTPClient.SECURITY_FTPES);
37. client.connect("192.168.1.122", 21);
38. client.login("123", "123123");
39. System.out.println(client.toString());
40. System.out.println(client.currentDirectory());
41. } catch (Exception e) {
42. e.printStackTrace();
43. }
44. }
45. }

package test;
import it.sauronsoftware.ftp4j.FTPClient;
import java.security.SecureRandom;
import java.security.cert.X509Certificate;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSocketFactory;
import javax.net.ssl.TrustManager;
import javax.net.ssl.X509TrustManager;
/*** 通过21端口进行显示FTPS连接* @说明 * @author cuisuqiang* @version 1.0* @since*/
public class Ftp4jTest {public static void main(String[] args) {try {TrustManager[] trustManager = new TrustManager[] { new X509TrustManager() {public X509Certificate[] getAcceptedIssuers() {return null;}public void checkClientTrusted(X509Certificate[] certs,String authType) {}public void checkServerTrusted(X509Certificate[] certs,String authType) {}} };SSLContext sslContext = null;sslContext = SSLContext.getInstance("SSL");sslContext.init(null, trustManager, new SecureRandom());SSLSocketFactory sslSocketFactory = sslContext.getSocketFactory();FTPClient client = new FTPClient();client.setSSLSocketFactory(sslSocketFactory);client.setSecurity(FTPClient.SECURITY_FTPES); client.connect("192.168.1.122", 21);client.login("123", "123123");System.out.println(client.toString());System.out.println(client.currentDirectory());} catch (Exception e) {e.printStackTrace();}}
}

代码会打印连接信息和当前目录

使用990端口进行隐式FTPS连接：

Java代码

1. package test;
2. import it.sauronsoftware.ftp4j.FTPClient;
3. import java.security.SecureRandom;
4. import java.security.cert.X509Certificate;
5. import javax.net.ssl.SSLContext;
6. import javax.net.ssl.SSLSocketFactory;
7. import javax.net.ssl.TrustManager;
8. import javax.net.ssl.X509TrustManager;
9. /**
10. * 进行隐式FTPS连接
11. * @说明
12. * @author cuisuqiang
13. * @version 1.0
14. * @since
15. */
16. public class Ftp4jTest {
17. public static void main(String[] args) {
18. try {
19. TrustManager[] trustManager = new TrustManager[] { new X509TrustManager() {
20. public X509Certificate[] getAcceptedIssuers() {
21. return null;
22. }
23. public void checkClientTrusted(X509Certificate[] certs,
24. String authType) {
25. }
26. public void checkServerTrusted(X509Certificate[] certs,
27. String authType) {
28. }
29. } };
30. SSLContext sslContext = null;
31. sslContext = SSLContext.getInstance("SSL");
32. sslContext.init(null, trustManager, new SecureRandom());
33. SSLSocketFactory sslSocketFactory = sslContext.getSocketFactory();
34. FTPClient client = new FTPClient();
35. client.setSSLSocketFactory(sslSocketFactory);
36. client.setSecurity(FTPClient.SECURITY_FTPS);
37. client.connect("192.168.1.122", 990);
38. client.login("123", "123123");
39. System.out.println(client.toString());
40. System.out.println(client.currentDirectory());
41. } catch (Exception e) {
42. e.printStackTrace();
43. }
44. }
45. }

package test;
import it.sauronsoftware.ftp4j.FTPClient;
import java.security.SecureRandom;
import java.security.cert.X509Certificate;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSocketFactory;
import javax.net.ssl.TrustManager;
import javax.net.ssl.X509TrustManager;
/*** 进行隐式FTPS连接* @说明 * @author cuisuqiang* @version 1.0* @since*/
public class Ftp4jTest {public static void main(String[] args) {try {TrustManager[] trustManager = new TrustManager[] { new X509TrustManager() {public X509Certificate[] getAcceptedIssuers() {return null;}public void checkClientTrusted(X509Certificate[] certs,String authType) {}public void checkServerTrusted(X509Certificate[] certs,String authType) {}} };SSLContext sslContext = null;sslContext = SSLContext.getInstance("SSL");sslContext.init(null, trustManager, new SecureRandom());SSLSocketFactory sslSocketFactory = sslContext.getSocketFactory();FTPClient client = new FTPClient();client.setSSLSocketFactory(sslSocketFactory);client.setSecurity(FTPClient.SECURITY_FTPS);client.connect("192.168.1.122", 990);client.login("123", "123123");System.out.println(client.toString());System.out.println(client.currentDirectory());} catch (Exception e) {e.printStackTrace();}}
}

打印内容相同

进行显示还是隐式连接的最大不同是指定了连接方式：

这个情况官方也给出了详细的说明：

The ftp4j library supports both FTPS (FTP over implicit TLS/SSL) and FTPES (FTP over explicit TLS/SSL).
The setSecurity() method can be used to turn on the feature:
client.setSecurity(FTPClient.SECURITY_FTPS); // enables FTPS
client.setSecurity(FTPClient.SECURITY_FTPES); // enables FTPES
Both methods must be called before connecting the remote server.
If the security is set to SECURITY_FTPS, the default port used by the connect() method changes to 990

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