在新的java版本1.7.0_21中重新编译java类后，使用BlazeDS调用Java函数时出错

Question

有人可以告诉我这个弹性堆栈跟踪的含义。我使用BlazeDS从flex调用java函数。该类都运行良好，但现在我已经使用java版本1.7.0_21重新编译了java类，它停止工作并抛出以下错误事件。 请告诉我出了什么问题。

(mx.rpc::Fault)#0
  errorID = 0
  faultCode = "Server.Processing"
  faultDetail = (null)
  faultString = "example/HelloWorld : Unsupported major.minor version 51.0 (unable to load class example.HelloWorld)"
  message = "faultCode:Server.Processing faultString:'example/HelloWorld : Unsupported major.minor version 51.0 (unable to load class example.HelloWorld)' faultDetail:'null'"
  name = "Error"
  rootCause = (Object)#1
    cause = (null)
    localizedMessage = "example/HelloWorld : Unsupported major.minor version 51.0 (unable to load class example.HelloWorld)"
    message = "example/HelloWorld : Unsupported major.minor version 51.0 (unable to load class example.HelloWorld)"

HelloWorld.java

package example;
    public class HelloWorld {

    public HelloWorld() {

    }

    public String getHelloWorld() {

    return "Hello Java World!";

    }

    public float addTwoNumbers(float a, float b)
    {
    return a+b;
    }

    }