Gson Utilities

Collection of utility classes to be used with google gson. These utilities are licensed under MIT license.

Using gson-utilities

To use this library, simply add this to your maven dependencies:

<dependency>
  <groupId>com.github.enerccio</groupId>
  <artifactId>gson-utilities</artifactId>
  <version>1.1.0</version>
</dependency>

Manual install

Clone the repository and run mvn package.

List of utilities

JsonBuilder

This utility builder provides a way to create JSON strings/values structurally but still using google gson as backing serializer.

Examples

Standard JSON builder

This is standard Java builder implementation that uses methods to create values.

String value = new JsonBuilder()
				.object()
					.property("texts").array()
						.string("Welcome to the hotel")
						.string("User %s!")
					.end()
					.property("singleton").bool(true)
					.property("configuration").object()
						.property("ip").string("127.0.0.1")
						.property("port").number(1234)
						.property("user").string("johnWick")
						.property("password").string("doggo")
						.property("isAdmin").bool(true)
						.property("maxResponseTimeSeconds").number(1.5)
					.end()
				.end()
				.toJson();

value will contain:

{
  "texts": [
    "Welcome to the hotel",
    "User %s!"
  ],
  "singleton": true,
  "configuration": {
    "ip": "127.0.0.1",
    "port": 1234,
    "user": "johnWick",
    "password": "doggo",
    "isAdmin": true,
    "maxResponseTimeSeconds": 1.5
  }
}

Functional JSON builder

You can use functional interface builders for objects/arrays in JsonBuilder.

Java <1.8

String value = new JsonBuilder()
			.setGson(gson)
			.object(new IObjectBuilder() {
				
				public void build(IObjectFacade root) {
					root.putArray("texts", new IArrayBuilder() {
						
						public void build(IArrayFacade texts) {
							texts.add("Welcome to the hotel");
							texts.add("User %s!");
						}
					});
					root.put("singleton", true);
					root.putObject("configuration", new IObjectBuilder() {
						
						public void build(IObjectFacade configuration) {
							configuration.put("ip", "127.0.0.1");
							configuration.put("port", 1234);
							configuration.put("user", "johnWick");
							configuration.put("password", "doggo");
							configuration.put("isAdmin", true);
							configuration.put("maxResponseTimeSeconds", 1.5);
						}
					});
				}
			})
			.toJson();

Java >=1.8

String value = new JsonBuilder()
			.object(root -> {
					root.putArray("texts", texts -> {
						texts.add("Welcome to the hotel");
						texts.add("User %s!");
					});
					root.put("singleton", true);
					root.putObject("configuration", configuration -> {
						configuration.put("ip", "127.0.0.1");
						configuration.put("port", 1234);
						configuration.put("user", "johnWick");
						configuration.put("password", "doggo");
						configuration.put("isAdmin", true);
						configuration.put("maxResponseTimeSeconds", 1.5);
					});
				})
			.toJson();

In both cases the value will be:

{
  "texts": [
    "Welcome to the hotel",
    "User %s!"
  ],
  "singleton": true,
  "configuration": {
    "ip": "127.0.0.1",
    "port": 1234,
    "user": "johnWick",
    "password": "doggo",
    "isAdmin": true,
    "maxResponseTimeSeconds": 1.5
  }
}

JSON Tree Visitors

These visitors allows to visit each element of JSON in the JSON string.

JsonTreeVisitor

This in memory visitor that deserializes JSON into JsonElements and then visits them. Supports also visiting already created JsonElement.

Examples

IJsonVisitor visitor = new JsonTreeVisitor();
visitor.setListener(new IJsonVisitorListener() {
	
	public void onElementStart(IJsonElementEntry entry) {
		// this is checked when element is about to be entered
	}
	
	public void onElementEnd(IJsonElementExit exit) {
		// This is checked when element is fully available
	}
});
visitor.visit(jsonString);

JsonStreamVisitor

Visits the JSON string stream like, ie JSON is not first deserialized then visited but it is being visited as it is being deserialized.

Optionally can return deserialized JsonElement.

Examples

IJsonVisitor visitor = new JsonStreamVisitor();
visitor.setListener(new IJsonVisitorListener() {
	
	public void onElementStart(IJsonElementEntry entry) {
		// this is checked when element is about to be entered
	}
	
	public void onElementEnd(IJsonElementExit exit) {
		// This is checked when element is fully available
	}
});
visitor.visit(jsonString);

For more available properties or visitors, see api doc.

Json Tree Matcher

When using visitors, both IJsonElementEntry and IJsonElementExit provide method getTree() which returns current nesting of properties and array indexes all up to current element. You can use JsonPatternMatcher to match against a pattern. For pattern syntax, see JsonPatternMatcher.

Json Helper

Collection of utilities related to work with JSON.

getFirst

Retrieves first JsonElement that matches the pattern provided (see Json Tree Matcher) and optionally predicate.

Examples

{ 
	"a":
	{ 
		"b" : 
		{
			"c": 
			{ 
				"d" : "x"
			}
		}
	}
}

JsonElement e = JsonHelper.getFirst(value, "a.b.c.d");
// e will contain JsonPrimitive with string value "x"

{ 
	"a":
	{ 
		"b" : 
		{
			"c": 
			{ 
				"d" : 4
			},
			"e":
			{
				"d" : "x"
			}
		}
	}
}

JsonElement e = JsonHelper.getFirst(value, "a.**.d", e -> {
	return e.isJsonPrimitive() && e.getAsJsonPrimitive().isString();
});
// e will contain JsonPrimitive with string value "x"

getAll

Same as with getFirst but retrieves list of all matching elements that optionally have to pass predicate.