您可以这样做：

String jsonInputString = """
    [{"Name": "1", "Partner": "11" },
     {"Name": "2"},
     {"Name": "3", "Partner": "33" } ]
"""

// parse the JSON into a List of Map
def maps = new JsonSlurper().parseText(jsonInputString)

def resultingMaps = maps.collect { map ->
    if(!map.containsKey('Partner')) {
        // the numbers in the initial map are Strings but
        // the question shows this one as a number, so here
        // it is a number, could just as well be a String with
        // the 0 in it...
        map.Partner = 0
    }
    map
}

// resultingMaps will be [[Name:1, Partner:11], [Name:2, Partner:0], [Name:3, Partner:33]]

编辑：

我刚接触Groovy，不确定如何继续，尝试了几个使用“WithDefault”的东西，但没有成功

withDefault可能不是您想要的，因为除非请求该密钥，否则它不会将0放入Map。你可以通过运行这个..。

def resultingMaps = maps.collect { map ->
    map.withDefault { key ->
        if(key == 'Partner') {
            return 0
        }
    }
}

// this will makes sure every Map has a "Partner" entry...
resultingMaps*.get('Partner')

// resultingMaps will be [[Name:1, Partner:11], [Name:2, Partner:0], [Name:3, Partner:33]]