tessl/maven-com-google-code-gson--gson
Java library for converting Java objects to JSON and vice-versa.
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Pending
json-tree-model.mddocs/
JSON Tree Model
Gson provides a tree-based API for building and manipulating JSON structures programmatically. This is useful when you need to modify JSON before serialization or after deserialization.
JsonElement Hierarchy
public abstract class JsonElement {
public abstract JsonElement deepCopy();
// Type checking methods
public boolean isJsonArray();
public boolean isJsonObject();
public boolean isJsonPrimitive();
public boolean isJsonNull();
// Conversion methods
public JsonObject getAsJsonObject();
public JsonArray getAsJsonArray();
public JsonPrimitive getAsJsonPrimitive();
public JsonNull getAsJsonNull();
// Primitive value extraction
public boolean getAsBoolean();
public Number getAsNumber();
public String getAsString();
public double getAsDouble();
public float getAsFloat();
public long getAsLong();
public int getAsInt();
public byte getAsByte();
public char getAsCharacter();
}JsonObject
Represents JSON objects with key-value pairs.
public final class JsonObject extends JsonElement {
public JsonObject();
public JsonObject deepCopy();
// Adding elements
public void add(String property, JsonElement value);
public void addProperty(String property, String value);
public void addProperty(String property, Number value);
public void addProperty(String property, Boolean value);
public void addProperty(String property, Character value);
// Accessing elements
public JsonElement get(String memberName);
public JsonPrimitive getAsJsonPrimitive(String memberName);
public JsonArray getAsJsonArray(String memberName);
public JsonObject getAsJsonObject(String memberName);
// Management
public JsonElement remove(String property);
public boolean has(String memberName);
public Set<Map.Entry<String, JsonElement>> entrySet();
public Set<String> keySet();
public int size();
public boolean isEmpty();
}Usage:
// Create JSON object programmatically
JsonObject person = new JsonObject();
person.addProperty("name", "Alice");
person.addProperty("age", 30);
person.addProperty("active", true);
// Convert to string
Gson gson = new Gson();
String json = gson.toJson(person);
// Result: {"name":"Alice","age":30,"active":true}
// Access properties
String name = person.get("name").getAsString();
int age = person.get("age").getAsInt();
boolean active = person.get("active").getAsBoolean();
// Check if property exists
if (person.has("email")) {
String email = person.get("email").getAsString();
}JsonArray
Represents JSON arrays.
public final class JsonArray extends JsonElement {
public JsonArray();
public JsonArray(int capacity);
public JsonArray deepCopy();
// Adding elements
public void add(JsonElement element);
public void add(Boolean bool);
public void add(Character character);
public void add(Number number);
public void add(String string);
// Accessing elements
public JsonElement get(int index);
// Management
public JsonElement remove(int index);
public boolean remove(JsonElement element);
public boolean contains(JsonElement element);
public int size();
public boolean isEmpty();
// Iteration
public Iterator<JsonElement> iterator();
}Usage:
// Create JSON array
JsonArray numbers = new JsonArray();
numbers.add(1);
numbers.add(2);
numbers.add(3);
// Convert to string
String json = gson.toJson(numbers);
// Result: [1,2,3]
// Access elements
for (int i = 0; i < numbers.size(); i++) {
int value = numbers.get(i).getAsInt();
System.out.println(value);
}
// Using iterator
for (JsonElement element : numbers) {
int value = element.getAsInt();
System.out.println(value);
}JsonPrimitive
Represents JSON primitive values (strings, numbers, booleans).
public final class JsonPrimitive extends JsonElement {
public JsonPrimitive(Boolean bool);
public JsonPrimitive(Number number);
public JsonPrimitive(String string);
public JsonPrimitive(Character c);
public JsonPrimitive deepCopy();
public boolean isBoolean();
public boolean isNumber();
public boolean isString();
}Usage:
JsonPrimitive stringValue = new JsonPrimitive("Hello");
JsonPrimitive numberValue = new JsonPrimitive(42);
JsonPrimitive boolValue = new JsonPrimitive(true);
// Check types
if (stringValue.isString()) {
String str = stringValue.getAsString();
}
if (numberValue.isNumber()) {
int num = numberValue.getAsInt();
double dbl = numberValue.getAsDouble();
}JsonNull
Represents JSON null values.
public final class JsonNull extends JsonElement {
public static final JsonNull INSTANCE;
public JsonNull deepCopy();
}Usage:
JsonObject obj = new JsonObject();
obj.add("nullValue", JsonNull.INSTANCE);Tree Conversion
Convert between objects and JSON trees:
// Object to tree
public JsonElement toJsonTree(Object src);
public JsonElement toJsonTree(Object src, Type typeOfSrc);
// Tree to object
public <T> T fromJson(JsonElement json, Class<T> classOfT) throws JsonSyntaxException;
public <T> T fromJson(JsonElement json, Type typeOfT) throws JsonSyntaxException;
public <T> T fromJson(JsonElement json, TypeToken<T> typeOfT) throws JsonSyntaxException;Usage:
// Object to tree
Person person = new Person("Bob", 25);
JsonElement tree = gson.toJsonTree(person);
// Modify the tree
JsonObject obj = tree.getAsJsonObject();
obj.addProperty("email", "bob@example.com");
// Tree back to object
Person modifiedPerson = gson.fromJson(obj, Person.class);
// Tree to JSON string
String json = gson.toJson(tree);JsonParser
Utility for parsing JSON strings into JsonElement trees.
public final class JsonParser {
public static JsonElement parseString(String json) throws JsonSyntaxException;
public static JsonElement parseReader(Reader reader) throws JsonIOException, JsonSyntaxException;
public static JsonElement parseReader(JsonReader reader) throws JsonIOException, JsonSyntaxException;
}Usage:
String json = "{\"name\":\"Alice\",\"age\":30}";
JsonElement element = JsonParser.parseString(json);
if (element.isJsonObject()) {
JsonObject obj = element.getAsJsonObject();
String name = obj.get("name").getAsString();
}JsonStreamParser
Streaming parser for processing multiple JSON values from a single reader.
public final class JsonStreamParser implements Iterator<JsonElement> {
public JsonStreamParser(Reader reader);
public JsonStreamParser(String json);
public boolean hasNext();
public JsonElement next() throws JsonParseException;
}Usage:
String multipleJson = "{\"name\":\"Alice\"} {\"name\":\"Bob\"} [1,2,3]";
JsonStreamParser parser = new JsonStreamParser(multipleJson);
while (parser.hasNext()) {
JsonElement element = parser.next();
System.out.println(element);
}Complex Tree Manipulation
Building nested structures:
JsonObject address = new JsonObject();
address.addProperty("street", "123 Main St");
address.addProperty("city", "Springfield");
JsonObject person = new JsonObject();
person.addProperty("name", "John");
person.add("address", address);
JsonArray hobbies = new JsonArray();
hobbies.add("reading");
hobbies.add("swimming");
person.add("hobbies", hobbies);Traversing complex structures:
JsonObject root = JsonParser.parseString(complexJson).getAsJsonObject();
for (Map.Entry<String, JsonElement> entry : root.entrySet()) {
String key = entry.getKey();
JsonElement value = entry.getValue();
if (value.isJsonObject()) {
JsonObject nested = value.getAsJsonObject();
// Process nested object
} else if (value.isJsonArray()) {
JsonArray array = value.getAsJsonArray();
for (JsonElement item : array) {
// Process array item
}
}
}Install with Tessl CLI
npx tessl i tessl/maven-com-google-code-gson--gson