A fully pluggable JSON streaming library abstraction allows you to take advantage of the native platform’s built-in JSON library support (for example the JSON library that is built into Android Honeycomb). The streaming library enables you to write optimized code for efficient memory usage that minimizes parsing and serialization time.
A big advantage of this JSON library is that the choice of low-level streaming library is fully
pluggable. There are three built-in choices, all of which extend JsonFactory. You
can easily plug in your own implementation.
JacksonFactory: Based on the popular Jackson library, which is
considered the fastest in terms of parsing/serialization speed. Our JSON library provides
JsonFactory implementations based on Jackson 2.GsonFactory: Based on the Google GSON library, which is a lighter-weight
option (small size) that is also fairly fast, though not as fast as Jackson.AndroidJsonFactory (@Beta): Based on the JSON library built into
Android Honeycomb (SDK 3.0) and higher, and that is identical to the Google GSON library.User-defined JSON data models allow you to define Plain Old Java Objects (POJOs) and define how the library parses and serializes them to and from JSON. The code snippets below are part of a more complete example, YouTube sample, which demonstrates these concepts.
The following JSON snippet shows the relevant fields of a typical YouTube video search:
{
"kind": "youtube#searchListResponse",
"pageInfo": {
"totalResults": 1000000,
"resultsPerPage": 5
},
"items": [
{
"kind": "youtube#searchResult",
"id": {
"kind": "youtube#video",
"videoId": "e6Tudp5lqt8"
},
"snippet": {
"publishedAt": "2020-06-25T23:18:43Z",
"channelId": "UCKwGZZMrhNYKzucCtTPY2Nw",
"title": "Video 1 Title",
"description": "Video 1 Description",
"thumbnails": {
"default": {
"url": "https://i.ytimg.com/vi/e6Tudp5lqt8/default.jpg",
"width": 120,
"height": 90
},
"medium": {
"url": "https://i.ytimg.com/vi/e6Tudp5lqt8/mqdefault.jpg",
"width": 320,
"height": 180
},
"high": {
"url": "https://i.ytimg.com/vi/e6Tudp5lqt8/hqdefault.jpg",
"width": 480,
"height": 360
}
}
}
},
{
"kind": "youtube#searchResult",
"id": {
"kind": "youtube#video",
"videoId": "o-NtLpiMpw0"
},
"snippet": {
"publishedAt": "2020-06-25T17:28:52Z",
"channelId": "UClljAz6ZKy0XeViKsohdjqA",
"title": "Video Title 2",
"description": "Video 2 Description",
"thumbnails": {
"default": {
"url": "https://i.ytimg.com/vi/o-NtLpiMpw0/default.jpg",
"width": 120,
"height": 90
},
"medium": {
"url": "https://i.ytimg.com/vi/o-NtLpiMpw0/mqdefault.jpg",
"width": 320,
"height": 180
},
"high": {
"url": "https://i.ytimg.com/vi/o-NtLpiMpw0/hqdefault.jpg",
"width": 480,
"height": 360
}
}
}
},
{
"kind": "youtube#searchResult",
"id": {
"kind": "youtube#video",
"videoId": "TPAahzXZFZo"
},
"snippet": {
"publishedAt": "2020-06-26T15:45:00Z",
"channelId": "UCR4Yfr8HAZJd9X24dwuAt1Q",
"title": "Video 3 Title",
"description": "Video 3 Description",
"thumbnails": {
"default": {
"url": "https://i.ytimg.com/vi/TPAahzXZFZo/default.jpg",
"width": 120,
"height": 90
},
"medium": {
"url": "https://i.ytimg.com/vi/TPAahzXZFZo/mqdefault.jpg",
"width": 320,
"height": 180
},
"high": {
"url": "https://i.ytimg.com/vi/TPAahzXZFZo/hqdefault.jpg",
"width": 480,
"height": 360
}
}
}
},
{
"kind": "youtube#searchResult",
"id": {
"kind": "youtube#video",
"videoId": "gBL-AelsdFk"
},
"snippet": {
"publishedAt": "2020-06-24T15:24:06Z",
"channelId": "UCFHZHhZaH7Rc_FOMIzUziJA",
"title": "Video 4 Title",
"description": "Video 4 Description",
"thumbnails": {
"default": {
"url": "https://i.ytimg.com/vi/gBL-AelsdFk/default.jpg",
"width": 120,
"height": 90
},
"medium": {
"url": "https://i.ytimg.com/vi/gBL-AelsdFk/mqdefault.jpg",
"width": 320,
"height": 180
},
"high": {
"url": "https://i.ytimg.com/vi/gBL-AelsdFk/hqdefault.jpg",
"width": 480,
"height": 360
}
}
}
},
{
"kind": "youtube#searchResult",
"id": {
"kind": "youtube#video",
"videoId": "9ofe8axKjH0"
},
"snippet": {
"publishedAt": "2020-06-26T11:59:32Z",
"channelId": "UCtNpbO2MtsVY4qW23WfnxGg",
"title": "Video 5 Title",
"description": "Video 5 Description",
"thumbnails": {
"default": {
"url": "https://i.ytimg.com/vi/9ofe8axKjH0/default.jpg",
"width": 120,
"height": 90
},
"medium": {
"url": "https://i.ytimg.com/vi/9ofe8axKjH0/mqdefault.jpg",
"width": 320,
"height": 180
},
"high": {
"url": "https://i.ytimg.com/vi/9ofe8axKjH0/hqdefault.jpg",
"width": 480,
"height": 360
}
}
}
}
]
}
Here’s one possible way to design the Java data classes to represent this:
public static class ListResponse {
@Key("items")
private List<SearchResult> searchResults;
@Key
private PageInfo pageInfo;
public List<SearchResult> getSearchResults() {
return searchResults;
}
public PageInfo getPageInfo() {
return pageInfo;
}
}
public static class PageInfo {
@Key
private long totalResults;
@Key
private long resultsPerPage;
public long getTotalResults() {
return totalResults;
}
public long getResultsPerPage() {
return resultsPerPage;
}
}
public static class SearchResult {
@Key
private String kind;
@Key("id")
private VideoId videoId;
@Key
private Snippet snippet;
public String getKind() {
return kind;
}
public VideoId getId() {
return videoId;
}
public Snippet getSnippet() {
return snippet;
}
}
public static class VideoId {
@Key
private String kind;
@Key
private String videoId;
public String getKind() {
return kind;
}
public String getVideoId() {
return videoId;
}
}
public static class Snippet {
@Key
private String publishedAt;
@Key
private String channelId;
@Key
private String title;
@Key
private String description;
public String getPublishedAt() {
return publishedAt;
}
public String getChannelId() {
return channelId;
}
public String getTitle() {
return title;
}
public String getDescription() {
return description;
}
public Map<String, Thumbnail> getThumbnails() {
return thumbnails;
}
}
public static class Thumbnail {
@Key
private String url;
@Key
private long width;
@Key
private long height;
public String getUrl() {
return url;
}
public long getWidth() {
return width;
}
public long getHeight() {
return height;
}
}
A fully supported HTTP JSON parser makes it easy to parse HTTP responses to objects of these user defined classes:
public static ListResponse parseJson(HttpResponse httpResponse) throws IOException {
ListResponse listResponse = httpResponse.parseAs(ListResponse.class);
if (listResponse.getSearchResults().isEmpty()) {
System.out.println("No results found.");
} else {
for (SearchResult searchResult : listResponse.getSearchResults()) {
System.out.println();
System.out.println("-----------------------------------------------");
System.out.println("Kind: " + searchResult.getKind());
System.out.println("Video ID: " + searchResult.getId().getVideoId());
System.out.println("Title: " + searchResult.getSnippet().getTitle());
System.out.println("Description: " + searchResult.getSnippet().getDescription());
}
}
return listResponse;
}
Use the @Key annotation to indicate fields that need to be parsed from or
serialized to JSON. By default, the @Key annotation uses the Java field name as the JSON key. To
override this, specify the value of the @Key annotation.
Fields that don’t have the @Key annotation are considered internal data and are not parsed from or
serialized to JSON.
Visibility of the fields does not matter, nor does the existence of the getter or setter methods. So
for example, the following alternative representation for VideoId would work in the example
given above:
public static class VideoId {
@Key
public String kind;
@Key
public String videoId;
}
Normally only the fields you declare are parsed when a JSON response is parsed. The actual Google+ activity feed response contains a lot of content that we are not using in our example. The JSON parser skips that other content when parsing the response from Google+.
To retain the other content, declare your class to extend GenericJson. Notice that
GenericJson implements Map, so we can use the get and put methods to set JSON
content. See Youtube sample for an example of how it was
used in the Snippet class above.
The JSON library supports any implementation of Map, which works similarly to GenericJson. The
downside, of course, is that you lose the static type information for the fields.
One advantage of this JSON library is its ability to support JSON nulls and distinguish them from undeclared JSON keys. Although JSON nulls are relatively rare, when they do occur they often cause confusion.
Google+ doesn’t use JSON null values, so the following example uses fictitious JSON data to illustrate what can happen:
{
"items": [
{
"id": "1",
"value": "some value"
},
{
"id": "2",
"value": null
}
{
"id": "3"
}
]
}
We might represent each item as follows:
public class Item {
@Key
public String id;
@Key
public String value;
}
For items 2 and 3, what should be in the value field? The problem is that there is no obvious way in
Java to distinguish between a JSON key that is undeclared and a JSON key whose value is JSON null.
This JSON library solves the problem by using Java null for the common case of an undeclared JSON
key, and a special “magic” instance of String (Data.NULL_STRING) to identify it as
a JSON null rather than a normal value.
The following example shows how you might take advantage of this functionality:
private static void show(List<Item> items) {
for (Item item : items) {
System.out.println("ID: " + item.id);
if (item.value == null) {
System.out.println("No Value");
} else if (Data.isNull(item.value)) {
System.out.print("Null Value");
} else {
System.out.println("Value: '" + item.value + "'");
}
}
}