使用Groovy MetaClass覆盖方法 [英] Using Groovy MetaClass to overwrite Methods

问题描述

我有一个使用服务来执行某些操作的POJO：

  public class PlainOldJavaObject {
 
私人IService服务; 
 
 public String publicMethod（String x）{
 return doCallService（x）; 
 
 $ b $ public String doCallService（String x）{
 if（service == null）{
 throw new RuntimeException（Service must not null）; 
} 
 return service.callX（x）; 
} 
 
 public interface IService {
 String callX（Object o）; 
 
 
 
 
 $ b我有一个Groovy测试用例：
  class GTest扩展GroovyTestCase {
 
 def testInjectedMockIFace（）{
 def pojo = new PlainOldJavaObject ：{callX：very groovy} as IService）
 assertvery groovy== pojo.publicMethod（arg）
} 
 
 def testMetaClass（）{
 def pojo = new PlainOldJavaObject（）
 pojo.metaClass.doCallService = {String s  - > 
no service
} 
 assertno service== pojo.publicMethod（arg）
} 
} 
  testInjectedMockIFace 按预期工作：POJO创建为动态实现 IService 。当调用 callX 时，它只会返回非常常见。这样，服务就被嘲笑了。然而，我不明白为什么第二个方法 testMetaClass 不能按预期工作，而是抛出一个NullPointerException当试图在服务对象上调用 callX 时。我认为我已经用这一行覆盖了 doCallService 方法： 
 
 
  pojo .metaClass.doCallService = {String s  - > 
  
我做错了什么？ 
 
 
谢谢！
解决方案
您的语法稍微偏离了一点。问题是pojo是一个Java对象，并没有metaClass。拦截使用ExpandoMetaClass调用PlainOldJavaObject的doCallService：
 
 
 
只需替换： 
 
 
  pojo.metaClass.doCallService = {String s  - > 
无服务
} 
  
与：
  PlainOldJavaObject.metaClass.doCallService = {String s  - > 
无服务
} 
  
 
I have a POJO that uses a service to do something:
public class PlainOldJavaObject {

    private IService service;

    public String publicMethod(String x) {
        return doCallService(x);
    }

    public String doCallService(String x) {
        if(service == null) {
            throw new RuntimeException("Service must not be null");
        }
        return service.callX(x);
    }

    public interface IService {
        String callX(Object o);
    }
}
And I have a Groovy test case:
class GTest extends GroovyTestCase {

    def testInjectedMockIFace() {
        def pojo = new PlainOldJavaObject( service: { callX: "very groovy" } as IService )
        assert "very groovy" == pojo.publicMethod("arg")
    }

    def testMetaClass() {
        def pojo = new PlainOldJavaObject()
        pojo.metaClass.doCallService = { String s ->
            "no service"
        }
        assert "no service" == pojo.publicMethod("arg")
    }
}
The first test method, testInjectedMockIFace works as expected: The POJO is created with a dynamic implementation of IService. When callX is invoked, it simply returns "very groovy". This way, the service is mocked out. 


However I don't understand why the second method, testMetaClass does not work as expected but instead throws a NullPointerException when trying to invoke callX on the service object. I thought I had overwritten the doCallService method with this line:
pojo.metaClass.doCallService = { String s ->
What am I doing wrong?

Thanks!
解决方案
Your syntax is a tiny bit off.  The problem is that pojo is a Java Object and does not have a metaClass.  To intercept calls to PlainOldJavaObject's doCallService using ExpandoMetaClass:

Just replace:
    pojo.metaClass.doCallService = { String s ->
        "no service"
    }
With:
    PlainOldJavaObject.metaClass.doCallService = { String s ->
        "no service"
    }


                        
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