Grails扩展HttpServletResponse元类

我需要在不创建子类的情况下向response.setHeader（）方法添加一些功能。我对它使用元类，如下所示：

//grails bootstrap
  def overrideHttpResponse(){

    def old_impl = javax.servlet.http.HttpServletResponseWrapper.metaClass.&setHeader
    println "Get set HEaders"
    println net.bull.javamelody.CounterServletResponseWrapper.metaClass.methods.findAll { it.name == "setHeader" }.join("\n")
    println old_impl
    //output
    //Get set HEaders
    //public void javax.servlet.http.HttpServletResponseWrapper.setHeader(java.lang.String,java.lang.String)
    // org.codehaus.groovy.runtime.MethodClosure@6f62b062

    javax.servlet.http.HttpServletResponseWrapper.metaClass.setHeader = {String name, String value ->
      if(name == "Content-disposition"){
        value = value.replace(", "," ").replace(","," ")
      }
      println "In here"
      old_impl.invoke(name,value)
    }
  }
  //controller code
      withFormat {
      html result
      json {
        def map = exportService.getPackageMap(packageInstance, result.titlesList)

        def json = map as JSON

          response.setHeader("Content-disposition", "attachment; filename=\"${filename}.json\"")
          response.contentType = "application/json"
          println response.class
          //class net.bull.javamelody.CounterServletResponseWrapper
          render json
      }

println "Get set HEaders"
println response.class.metaClass.methods.findAll { it.name == "setHeader" }.join("\n")
def old_impl = javax.servlet.http.HttpServletResponseWrapper.metaClass.getMetaMethod("setHeader",[String,String] as Class[])
println old_impl
//Get set HEaders
//public void javax.servlet.http.HttpServletResponseWrapper.setHeader(java.lang.String,java.lang.String)
//public abstract void javax.servlet.http.HttpServletResponse.setHeader(java.lang.String,java.lang.String)

有什么建议可以解释为什么上述方法不起作用吗？我已经添加了打印输出作为注释，但是没有从元类中获取打印，内容配置值没有更改。我也试过这样：

//grails bootstrap
  def overrideHttpResponse(){

    def old_impl = javax.servlet.http.HttpServletResponseWrapper.metaClass.&setHeader
    println "Get set HEaders"
    println net.bull.javamelody.CounterServletResponseWrapper.metaClass.methods.findAll { it.name == "setHeader" }.join("\n")
    println old_impl
    //output
    //Get set HEaders
    //public void javax.servlet.http.HttpServletResponseWrapper.setHeader(java.lang.String,java.lang.String)
    // org.codehaus.groovy.runtime.MethodClosure@6f62b062

    javax.servlet.http.HttpServletResponseWrapper.metaClass.setHeader = {String name, String value ->
      if(name == "Content-disposition"){
        value = value.replace(", "," ").replace(","," ")
      }
      println "In here"
      old_impl.invoke(name,value)
    }
  }
  //controller code
      withFormat {
      html result
      json {
        def map = exportService.getPackageMap(packageInstance, result.titlesList)

        def json = map as JSON

          response.setHeader("Content-disposition", "attachment; filename=\"${filename}.json\"")
          response.contentType = "application/json"
          println response.class
          //class net.bull.javamelody.CounterServletResponseWrapper
          render json
      }

println "Get set HEaders"
println response.class.metaClass.methods.findAll { it.name == "setHeader" }.join("\n")
def old_impl = javax.servlet.http.HttpServletResponseWrapper.metaClass.getMetaMethod("setHeader",[String,String] as Class[])
println old_impl
//Get set HEaders
//public void javax.servlet.http.HttpServletResponseWrapper.setHeader(java.lang.String,java.lang.String)
//public abstract void javax.servlet.http.HttpServletResponse.setHeader(java.lang.String,java.lang.String)

此外，在我的控制器中，我再次尝试了此操作，返回的文件名没有任何更改：

   def old_impl = response.class.metaClass.getMetaMethod("setHeader",[String,String] as Class[])
   println old_impl
   //public abstract void javax.servlet.http.HttpServletResponse.setHeader(java.lang.String,java.lang.String)

    response.class.metaClass.setHeader = {String name, String value ->
      if(name == "Content-disposition"){
        value = value.replace(", "," ").replace(","," ")
      }
      println "In here"
      old_impl.invoke(name,value)
    }