json串中怎么把值为null的属性过滤掉

json串中如何把值为null的属性过滤掉
例如:{"a":1,"b":2,"c":null,"d":[{"aa":[{"aaa":null,"bbb":222}],"bb":22,"cc":null}]}
需要返回:
{"a":1,"b":2,"d":[{"aa":[{"bbb":222}],"bb":22}]}
求大大们指点....

[解决办法]

        String s = ":{"a":1,"b":2,"c":null,"d":[{"aa":[{"aaa":null,"bbb":222}],"bb":22,"cc":null}]}";
        // 把形如："a":null, 把后面有个逗号的给替换掉，这个替换掉，如果最后一个，cc:null是无法替换掉的
        s = s.replaceAll(""[^"]+":null,", "");
        // 把形如：,"a":null 把前面有个逗号的给替换掉
        s = s.replaceAll(","[^"]+":null", "");
        System.out.println(s);

:{"a":1,"b":2,"d":[{"aa":[{"bbb":222}],"bb":22}]}