Java - JSON分析器错误

Question

I am creating an application which it will send http request to a web server. The return will be in json . Here is how the json look like

[//I used a tool to make it beautiful and easy to read.
  {
    "item_name": "Adame",
    "item_type": "Special",
    "item": "Chestplate",
    "item_min_lvl": "50",
    "enchantment": {
      "health": "0.3",
      "dam": "24%",
      "life": "0.1",
      "xp": "24%",
      "loot": "22%"
    },
    "def": "73"
  },
  {
    "item_name": "Sticks'",
    "item_type": "Unique",
    "item": "Stick",
    "item_min_lvl": "4",
    "enchantment": {
      "health": "0.6",
      "mana": "1",
      "dam": "12%",
      "life": "0.3",
      "xp": "17%",
      "loot": "17%"
    },
    "min_dam": "39",
    "max_dam": "34"
  },
  {
    "item_name": "Sword'",
    "item_type": "Unique",
    "item": "Sword",
    "item_min_lvl": "8",
    "enchantment": [], //colonm 30 is [
    "min_dam": "9",
    "max_dam": "10"
  }
]

Are you can see, the data inside the array are different. I got this error, Expected BEGIN_OBJECT but was BEGIN_ARRAY at line 1 column 30 . This is my code:

MyJSON[] data = gson.from(jsonString, MyJSON[].class);

class MyJSON {
    String item_name;
    String item_type;
    String item;
    String item_min_lvl;
    Enchantment enchantment;
    String min_dam;
    String max_dam;

    @Override
    public String toString() {
        StringBuilder builder = new StringBuilder();

        builder.append("\nitem_name:").append(item_name);
        builder.append("\nitem_type:").append(item_type);
        builder.append("\nitem:").append(item);
        builder.append("\nitem_min_lvl:").append(item_min_lvl);

        builder.append("\n\nEnchantment Details:");
        builder.append("\nhealth:").append(enchantment.health);
        builder.append("\ndam:").append(enchantment.dam);
        builder.append("\nlife:").append(enchantment.life);
        builder.append("\nxp:").append(enchantment.xp);
        builder.append("\nloot:").append(enchantment.loot);
        return builder.toString();
    }
}

class Enchantment {
    String health;
    String dam;
    String life;
    String xp;
    String loot;
    String mana;
}

Can anyone help me to improve my code so my code an parse the json in different case. Thanks in advanced. (Ps that's not my web server so I can't do anything with the json)

Answer 1

Basically this line of JSON

"enchantment": [], //colonm 30 is [

doesn't match your POJO. You're expecting an Enchantment object, but the JSON is giving you an array. Fix your JSON to return an empty JSON object or nothing at all for the enchantment pair.

"enchantment": {}

Answer 2

You can create a custom list type in Gson's fromJson() method to map it to a list of POJOs

Type listType = new TypeToken<ArrayList<Enhancement>>() {}.getType();
List<Enhancement> enhancements = new Gson().fromJson(jsonString, listType);

You will get a List<Enhancement> .

Answer 3

This is a Valid JSON unless you have added comments just to show lines where is the issue?

Comments should not be part of JSON.

Here is the code that I have already shared you at you another post Java - Json deserialize data [] .

You have to use ArrayList<Map<String, Object>> because the entries in the JSON string are not symmetric. You can't convert it into POJO in this case.

StringBuilder builder = new StringBuilder();
BufferedReader reader = new BufferedReader(new FileReader(new File("resources/json2.txt")));
String line = null;
while ((line = reader.readLine()) != null) {
    builder.append(line);
}
reader.close();

Gson gson = new Gson();
Type listType = new TypeToken<ArrayList<Map<String, Object>>>() {
}.getType();
ArrayList<Map<String, Object>> list = gson.fromJson(builder.toString(), listType);

for (Map<String, Object> json : list) {
    for (String key : json.keySet()) {
        System.out.println(key + ":" + json.get(key));
    }
    System.out.println("===========");
}

output:

item_name:Adame
item_type:Special
item:Chestplate
item_min_lvl:50
enchantment:{health=0.3, dam=24%, life=0.1, xp=24%, loot=22%}
def:73
===========
item_name:Sticks'
item_type:Unique
item:Stick
item_min_lvl:4
enchantment:{health=0.6, mana=1, dam=12%, life=0.3, xp=17%, loot=17%}
min_dam:39
max_dam:34
===========
item_name:Sword'
item_type:Unique
item:Sword
item_min_lvl:8
enchantment:[]
min_dam:9
max_dam:10
===========

---

EDIT

enchantment return something like

enchantment:{health=0.6, mana=1, dam=12%, life=0.3, xp=17%, loot=17%}. 

How can I get for example health?

Type mapType = new TypeToken<Map<String, String>>() {
}.getType();
String string = "{health=0.6, mana=1, dam=12%, life=0.3, xp=17%, loot=17%}";
Map<String, String> map = new Gson().fromJson(string, mapType);
for (String key : map.keySet()) {
    System.out.println(key + ":" + map.get(key));
}

output:

health:0.6
mana:1
dam:12%
life:0.3
xp:17%
loot:17%