How to add jenkins node via Java program - jenkins

Question

I must manage Jenkins node via a Java program. I found this example but when I launch it do nothing, no error e no result on Jenkins interface:
#Test
public void test() {
//fail("Not yet implemented");
//Main.main(new String[]{"-version"});
//Main.main(new String[]{"-s", "http://localhost:8080", "-auth", "admin:password", "list-plugins"});
//Main.main(new String[]{"-ssh"});
StringBuilder str = new StringBuilder("<slave>");
str.append(" <name>nodo-test</name>");
str.append(" <description>test</description>");
str.append(" <remoteFS>/home/build/jenkins-node</remoteFS>");
str.append(" <numExecutors>1</numExecutors>");
str.append(" <mode>NORMAL</mode>");
str.append(" <retentionStrategy class=\"hudson.slaves.RetentionStrategy$Always\"/>");
str.append(" <launcher class=\"hudson.plugins.sshslaves.SSHLauncher\" plugin=\"ssh-slaves#1.5\">");
str.append(" <host>nodo-test</host>");
str.append(" <port>22</port>");
str.append(" <credentialsId>xxxxxx</credentialsId>");
str.append(" </launcher>");
str.append(" <label>build</label>");
str.append(" <nodeProperties/>");
str.append(" <userId>Marco</userId>");
str.append("</slave>");
//Main.main(new String[]{"-s", "http://localhost:8080", "-auth", "admin:password", "create-node", str.toString()});
Process process;
try {
process = Runtime.getRuntime().exec("java -jar ./jenkins-cli.jar -s http://localhost:8080/jenkins create-node nodo-test");
OutputStream stdin = process.getOutputStream();
InputStream stdout = process.getInputStream();
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(stdin));
writer.write(str.toString());
writer.flush();
writer.close();
System.out.println("End runtime");
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("End");
}
What is wrong ? Is there a method to do the same thing without use jenkins-cli ?
Thanks for your support.
UPDATE:
the code, in effect, show error on "flush": "Pipe is being closed".
FYI I'm trying to add a node to a Jenkins server running in a docker image "localhost:8080".