Jetty's default configuration has a limitation on POST data （200000 bytes）that
prevents Hudson from reading the Update Center data (available
plugins). Jetty gets an error like java.lang.IllegalStateException: Form too large. To resolve this, add something like this to jetty.xml:

Jetty 6:

在jetty.xml中设置该参数

<Call class="java.lang.System" name="setProperty">

      <Arg>org.mortbay.jetty.Request.maxFormContentSize</Arg>

      <Arg>-1</Arg>

    </Call>

Jetty 7:

<Call class="java.lang.System" name="setProperty">
  <Arg>org.eclipse.jetty.server.Request.maxFormContentSize</Arg>
  <Arg>-1</Arg>
</Call>