Adding Custom Methods to fastjson JSONObject Using Groovy MetaClass

The article builds on a previous tutorial about Groovy dynamic method and property addition, and shows how to use fastjson to add a custom method to JSONObject for more efficient programming.

Requirement

fastjson's com.alibaba.fastjson.JSONObject does not provide a direct iteration method, so developers often need to write explicit loops or lambda expressions to print parts of a JSON response during API testing.

Sample JSON Data

def params = new JSONObject()
params.code= 1
params.msg= "FunTester"
def data = new JSONObject()
data.name = "张三"
data.age = 22
params.data = []
params.data << data
params.data << data.clone()
params.data << data.clone()

Printing the above JSON yields a formatted output showing the msg , code , and an array of data objects.

Direct Implementation of Output Method

The solution uses groovy.lang.MetaClass to inject a new method into JSONObject :

JSONObject.metaClass.fun = {
    def array = params.getJSONArray("data")
    array.each {
        sleep(1.0)
        output(Time.getNow(Time.DEFAULT_FORMAT.get()))
        output(it)
    }
}

params.fun()

Running this prints each element of the data array with timestamps, as shown in the console logs.

Flexible Implementation Using Closures

By employing groovy.lang.Closure , the same functionality can be expressed more concisely:

JSONObject.metaClass.fun2 = { f ->
    def array = params.getJSONArray("data")
    array.each {
        f(it)
    }
}

params.fun2({x -> output(x.get("name"))})
params.fun2({output(it.get("age"))})

The console output displays the names and ages of the objects in the JSON array.

Conclusion

Using Groovy's MetaClass and closures to extend fastjson.JSONObject provides a powerful way to add custom traversal and printing methods, reducing boilerplate code and improving readability in API testing scripts.