Use ServiceLoader to define the default SSH session factory.

Use ServiceLoader and define
org.eclipse.jgit.transport.DefaultSshSessionFactory in
META-INF/services/org.eclipse.jgit.transport.SshSessionFactory so that
the legacy behavior is still the same.

Bug: 553625
Change-Id: Id1a65506140d921ed76d83699e3817f0d2ca08ed
Signed-off-by: Emmanuel Hugonnet <ehugonne@redhat.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/resources/META-INF/services/org.eclipse.jgit.transport.SshSessionFactory

@@ -0,0 +1 @@
+org.eclipse.jgit.transport.DefaultSshSessionFactory

org.eclipse.jgit/src/org/eclipse/jgit/transport/DefaultSshSessionFactory.java

@@ -24,8 +24,10 @@ import com.jcraft.jsch.Session;
  * <p>
  * If user interactivity is required by SSH (e.g. to obtain a password), the
  * connection will immediately fail.
+ *
+ * @since 5.7
  */
-class DefaultSshSessionFactory extends JschConfigSessionFactory {
+public class DefaultSshSessionFactory extends JschConfigSessionFactory {
 	/** {@inheritDoc} */
 	@Override
 	protected void configure(OpenSshConfig.Host hc, Session session) {

org.eclipse.jgit/src/org/eclipse/jgit/transport/SshSessionFactory.java

@@ -13,6 +13,8 @@ package org.eclipse.jgit.transport;
 
 import java.security.AccessController;
 import java.security.PrivilegedAction;
+import java.util.Iterator;
+import java.util.ServiceLoader;
 
 import org.eclipse.jgit.errors.TransportException;
 import org.eclipse.jgit.lib.Constants;
@@ -31,8 +33,16 @@ import org.eclipse.jgit.util.SystemReader;
  * SshSessionFactory for the duration of the period they are using the Session.
  */
 public abstract class SshSessionFactory {
-	private static SshSessionFactory INSTANCE = new DefaultSshSessionFactory();
+	private static SshSessionFactory INSTANCE = loadSshSessionFactory();
 
+	private static SshSessionFactory loadSshSessionFactory() {
+		ServiceLoader<SshSessionFactory> loader = ServiceLoader.load(SshSessionFactory.class);
+		Iterator<SshSessionFactory> iter = loader.iterator();
+		if(iter.hasNext()) {
+			return iter.next();
+		}
+		return null;
+	}
 	/**
 	 * Get the currently configured JVM-wide factory.
 	 * <p>