json格式如下：
{
"msg":"success",
"total":0,
"code":0,
"data":[
{
"productId":32,
"picDetail":"detail1.png",
"pic":"p1.png"
},
{
"productId":31,
"picDetail":"detail2.png",
"pic":"p2.png"
}
]
}

代码示例：
安装依赖：

 <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.78</version>
        </dependency>

public class JsonStudy {
    public static void main(String[] args) {
        String ajson = "{\"msg\":\"success\",\"total\":0,\"code\":0,\"data\":[{\"productId\":32,\"picDetail\":\"detail1.png\",\"pic\":\"p1.png\"},{\"productId\":31,\"picDetail\":\"detail2.png\",\"pic\":\"p2.png\"}]}";
        JSONObject jsonObject = (JSONObject) JSONObject.parse(ajson);
        System.out.println(jsonObject.toString());
        //获取 msg
        System.out.println(jsonObject.get("msg"));
        JSONArray jsonArray = jsonObject.getJSONArray("data");
        System.out.println(jsonArray.get(0).toString());
        String a = jsonArray.get(0).toString();
        JSONObject jsonObject1 = (JSONObject) JSONObject.parse(a);
        //获取productId
        System.out.println(jsonObject1.get("productId"));

    }

}