title: why set port to 80 failed in undertow server? (java)
body: <p>When I "mvn exec:java" the java program, I have problems to set port to 80, but 8080 can be successful.</p>
  
  <pre><code> Undertow server = Undertow.builder()
                      .addHttpListener(80, "localhost")
                      .setHandler(path)
                      .build();
              server.start();
  </code></pre>
  
  <p>when I set it as 80, i got exceptions like</p>
  
  <pre><code>java.lang.reflect.InvocationTargetException
      at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
      at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
      at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
      at java.lang.reflect.Method.invoke(Method.java:498)
      at org.codehaus.mojo.exec.ExecJavaMojo$1.run(ExecJavaMojo.java:297)
      at java.lang.Thread.run(Thread.java:745)
  Caused by: java.lang.RuntimeException: java.net.SocketException: Permission denied
          at io.undertow.Undertow.start(Undertow.java:141)
          at cc.cmu.edu.Q1.Q1Controller.main(Q1Controller.java:46)
          ... 6 more
  Caused by: java.net.SocketException: Permission denied
          at sun.nio.ch.Net.bind0(Native Method)
          at sun.nio.ch.Net.bind(Net.java:433)
          at sun.nio.ch.Net.bind(Net.java:425)
          at sun.nio.ch.ServerSocketChannelImpl.bind(ServerSocketChannelImpl.java:223)
          at sun.nio.ch.ServerSocketAdaptor.bind(ServerSocketAdaptor.java:74)
          at sun.nio.ch.ServerSocketAdaptor.bind(ServerSocketAdaptor.java:67)
          at org.xnio.nio.NioXnioWorker.createTcpConnectionServer(NioXnioWorker.java:175)
          at org.xnio.XnioWorker.createStreamConnectionServer(XnioWorker.java:242)
          at io.undertow.Undertow.start(Undertow.java:120)
          ... 7 more
  </code></pre>