Parsing a complex Json Object using GSON in Java

Question

I have a very long JSON to parse with Gson, but for brevity I have trimmed it to this example:

{  "volumes": [   {    "status": "available",     "managed": true,     "name": "va_85621143-1133-412f-83b4-57a01a552638_",     "support": {     "status": "supported"    },     "storage_pool": "pfm9253_pfm9254_new",     "id": "afb8e294-6188-4907-9f6f-963c7623cecb",     "size": 9   },    {    "status": "in-use",     "managed": false,     "name": "bt_newd20",     "support": {     "status": "not_supported",      "reasons": [      "This volume is not a candidate for management because it is already attached to a virtual machine.  To manage this volume with PowerVC, select the virtual machine to which the volume is attached for management. The attached volume will be automatically included for management."     ]    },     "storage_pool": "KVM",     "mapped_wwpns": [     "2101001B32BD4280",      "2100001B329D4280",      "2101001B32BD637E",      "2100001B329D637E"    ],     "id": "c7838c79-17ca-3cbc-98e5-3567fde902d8",     "size": 0   },    {    "status": "available",     "managed": true,     "name": "vdisk138",     "support": {     "status": "supported"    },     "storage_pool": "Chassis2_IBMi",     "id": "b6d00783-9f8c-40b8-ad78-956b0299478c",     "size": 100     }  ] } 

From SO and few other places, I have found that I need to define a top level container like one below but I do not know how to complete its definition

static class VolumeContainer {          //I don't know what do in here. This is the first problem  } 

and then a class for each Volume

static class Volume {    private String status;    private boolean managed;    private String name;     //This is the second problem.The "support" variable should not be a string.    //It is in {}. Just for information, I won't use it.    //private String support;     private String storagePool;    private List<String> mapped_wwpns;    private String id;    private String size;  } 

I am trying to parse it and this is what I coded so far:

JsonParser parser = new JsonParser(); JsonObject obj = parser.parse(response).getAsJsonObject();  Gson gson = new Gson(); 

The JSON string is stored in a variable named response

VolumeContainer vc = gson.fromJson(response,VolumeContainer.class); 

My final requirement is a HashTable of id and associated name.

Answer 1

First problem: your VolumeContainer needs to be:

public class VolumeContainer {    public List<Volume> volumes; } 

it does not need to be static.

Second problem: your Volume class should be like this:

public class Volume {   private String status;    private Boolean managed;    private String name;    private Support support;    private String storage_pool;    private String id;    private int size;   private List<String> mapped_wwpns;    public String getId(){return id;}   public String getName(){return name;} } 

I defined a class named Support like this:

public class Support {    private String status;    private List<String> reasons; } 

Third problem: parsing, If response string contains your example data, simply parse like this:

Gson g = new Gson(); VolumeContainer vc = g.fromJson(response, VolumeContainer.class); 

Fourth problem: get the map. Finally to get your HashMap, just do like this:

HashMap<String, String> hm = new HashMap<String,String>(); for(Volume v: vc.volumes){   hm.put(v.getId(), v.getName());   }