Java - Json deserialize data []

问题

I am new to stackoverflow.

I am creating an Java application which it will get data from a web server. The data is in json format. Example"

[
  {
    "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"
  }
]

I know how to deserialize json using Gson. As you can see, it's started with [. I never deserialize this case before. Also, the json data is not the same(e.g. enchantment). I also searched in Google but I can't find any similar case. Can anyone help me with the code? Thanks in advanced.

回答1:

Try with this code. You will get the answer of your question. It's an List with 2 items.

StringBuilder builder = new StringBuilder();
BufferedReader reader = new BufferedReader(new FileReader(new File("resources/json1.txt")));
String line = null;
while ((line = reader.readLine()) != null) {
    builder.append(line);
}
reader.close();

Gson gson = new Gson();
Type listType = new TypeToken<ArrayList<MyJSON>>() {
}.getType();
List<MyJSON> list = gson.fromJson(builder.toString(), listType);
// you can try this form as well
// MyJSON[] list = gson.fromJson(builder.toString(), MyJSON[].class);

for (MyJSON json : list) {
    System.out.println(json.toString());
}

...

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

    @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;
}

output:

item_name:Adame
item_type:Special
item:Chestplate
item_min_lvl:50

Enchantment Details:
health:0.3
dam:24%
life:0.1
xp:24%
loot:22%


item_name:Sticks'
item_type:Unique
item:Stick
item_min_lvl:4

Enchantment Details:
health:0.6
dam:12%
life:0.3
xp:17%
loot:17%

---

EDIT

The structure of each entry is not same hence you can't use POJO for this type of JSON.

Simply use ArrayList<Map<String, Object>> and access the value based on key from the map.

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
===========

回答2:

This is actually valid in Java and with GSON:

YourObject[] locs = gson.fromJson (someJsonString, YourObject[].class);

It'll parse and return an array of YourObject. Just create Java Classes that represent your JSON objects, and replace the placeholders as necessary.

EDIT: As Braj said before, you can create a fully formed POJO, including the other, (non-symmetrical) attributes (I'm borrowing the code from from Braj's answer here):

//... snip ...
class MyJSON
{
    String      item_name;
    String      item_type;
    String      item;
    String      item_min_lvl;
    Enchantment enchantment;

    // Heres the other attributes
    String      min_dam;
    String      max_dam;
}
//... snip ...

GSON will parse it and set the values to null if they aren't provided in the original JSON.

However, from the other question, it seems that the JSON (Java - JSON Parser Error) for enchantment is provided inconsistently, so this will cause issues. I would recommend sending JSON for enchantment as an array for consistency, then you could structure your POJO as:

 //... snip ...
class MyJSON
{
    String      item_name;
    String      item_type;
    String      item;
    String      item_min_lvl;
    Enchantment[]   enchantment;

    // Heres the other attributes
    String      min_dam;
    String      max_dam;
}
//... snip ...

来源：https://stackoverflow.com/questions/23710037/java-json-deserialize-data