com.google.gson.JsonElement Maven / Gradle / Ivy
The newest version!
/*
* Copyright (C) 2008 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.gson;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.gson.internal.Streams;
import com.google.gson.stream.JsonWriter;
import java.io.IOException;
import java.io.Reader;
import java.io.StringWriter;
import java.math.BigDecimal;
import java.math.BigInteger;
/**
* A class representing an element of JSON. It could either be a {@link JsonObject}, a {@link
* JsonArray}, a {@link JsonPrimitive} or a {@link JsonNull}.
*
* This class provides multiple {@code getAs} methods which allow
*
*
* - obtaining the represented primitive value, for example {@link #getAsString()}
*
- casting to the {@code JsonElement} subclasses in a convenient way, for example {@link
* #getAsJsonObject()}
*
*
* Converting {@code JsonElement} from / to JSON
*
* There are two ways to parse JSON data as a {@link JsonElement}:
*
*
* - {@link JsonParser}, for example:
*
* JsonObject jsonObject = JsonParser.parseString("{}").getAsJsonObject();
*
* - {@link Gson#fromJson(Reader, Class) Gson.fromJson(..., JsonElement.class)}
* It is possible to directly specify a {@code JsonElement} subclass, for example:
*
* JsonObject jsonObject = gson.fromJson("{}", JsonObject.class);
*
*
*
* To convert a {@code JsonElement} to JSON either {@link #toString() JsonElement.toString()} or the
* method {@link Gson#toJson(JsonElement)} and its overloads can be used.
*
* It is also possible to obtain the {@link TypeAdapter} for {@code JsonElement} from a {@link
* Gson} instance and then use it for conversion from and to JSON:
*
*
{@code
* TypeAdapter adapter = gson.getAdapter(JsonElement.class);
*
* JsonElement value = adapter.fromJson("{}");
* String json = adapter.toJson(value);
* }
*
* {@code JsonElement} as JSON data
*
* {@code JsonElement} can also be treated as JSON data, allowing to deserialize from a {@code
* JsonElement} and serializing to a {@code JsonElement}. The {@link Gson} class offers these
* methods for this:
*
*
* - {@link Gson#fromJson(JsonElement, Class) Gson.fromJson(JsonElement, ...)}, for example:
*
* JsonObject jsonObject = ...;
* MyClass myObj = gson.fromJson(jsonObject, MyClass.class);
*
* - {@link Gson#toJsonTree(Object)}, for example:
*
* MyClass myObj = ...;
* JsonElement json = gson.toJsonTree(myObj);
*
*
*
* The {@link TypeAdapter} class provides corresponding methods as well:
*
*
* - {@link TypeAdapter#fromJsonTree(JsonElement)}
*
- {@link TypeAdapter#toJsonTree(Object)}
*
*
* @author Inderjeet Singh
* @author Joel Leitch
*/
public abstract class JsonElement {
/**
* @deprecated Creating custom {@code JsonElement} subclasses is highly discouraged and can lead
* to undefined behavior.
* This constructor is only kept for backward compatibility.
*/
@Deprecated
public JsonElement() {}
/**
* Returns a deep copy of this element. Immutable elements like primitives and nulls are not
* copied.
*
* @since 2.8.2
*/
public abstract JsonElement deepCopy();
/**
* Provides a check for verifying if this element is a JSON array or not.
*
* @return true if this element is of type {@link JsonArray}, false otherwise.
*/
public boolean isJsonArray() {
return this instanceof JsonArray;
}
/**
* Provides a check for verifying if this element is a JSON object or not.
*
* @return true if this element is of type {@link JsonObject}, false otherwise.
*/
public boolean isJsonObject() {
return this instanceof JsonObject;
}
/**
* Provides a check for verifying if this element is a primitive or not.
*
* @return true if this element is of type {@link JsonPrimitive}, false otherwise.
*/
public boolean isJsonPrimitive() {
return this instanceof JsonPrimitive;
}
/**
* Provides a check for verifying if this element represents a null value or not.
*
* @return true if this element is of type {@link JsonNull}, false otherwise.
* @since 1.2
*/
public boolean isJsonNull() {
return this instanceof JsonNull;
}
/**
* Convenience method to get this element as a {@link JsonObject}. If this element is of some
* other type, an {@link IllegalStateException} will result. Hence it is best to use this method
* after ensuring that this element is of the desired type by calling {@link #isJsonObject()}
* first.
*
* @return this element as a {@link JsonObject}.
* @throws IllegalStateException if this element is of another type.
*/
public JsonObject getAsJsonObject() {
if (isJsonObject()) {
return (JsonObject) this;
}
throw new IllegalStateException("Not a JSON Object: " + this);
}
/**
* Convenience method to get this element as a {@link JsonArray}. If this element is of some other
* type, an {@link IllegalStateException} will result. Hence it is best to use this method after
* ensuring that this element is of the desired type by calling {@link #isJsonArray()} first.
*
* @return this element as a {@link JsonArray}.
* @throws IllegalStateException if this element is of another type.
*/
public JsonArray getAsJsonArray() {
if (isJsonArray()) {
return (JsonArray) this;
}
throw new IllegalStateException("Not a JSON Array: " + this);
}
/**
* Convenience method to get this element as a {@link JsonPrimitive}. If this element is of some
* other type, an {@link IllegalStateException} will result. Hence it is best to use this method
* after ensuring that this element is of the desired type by calling {@link #isJsonPrimitive()}
* first.
*
* @return this element as a {@link JsonPrimitive}.
* @throws IllegalStateException if this element is of another type.
*/
public JsonPrimitive getAsJsonPrimitive() {
if (isJsonPrimitive()) {
return (JsonPrimitive) this;
}
throw new IllegalStateException("Not a JSON Primitive: " + this);
}
/**
* Convenience method to get this element as a {@link JsonNull}. If this element is of some other
* type, an {@link IllegalStateException} will result. Hence it is best to use this method after
* ensuring that this element is of the desired type by calling {@link #isJsonNull()} first.
*
* @return this element as a {@link JsonNull}.
* @throws IllegalStateException if this element is of another type.
* @since 1.2
*/
@CanIgnoreReturnValue // When this method is used only to verify that the value is JsonNull
public JsonNull getAsJsonNull() {
if (isJsonNull()) {
return (JsonNull) this;
}
throw new IllegalStateException("Not a JSON Null: " + this);
}
/**
* Convenience method to get this element as a boolean value.
*
* @return this element as a primitive boolean value.
* @throws UnsupportedOperationException if this element is not a {@link JsonPrimitive} or {@link
* JsonArray}.
* @throws IllegalStateException if this element is of the type {@link JsonArray} but contains
* more than a single element.
*/
public boolean getAsBoolean() {
throw new UnsupportedOperationException(getClass().getSimpleName());
}
/**
* Convenience method to get this element as a {@link Number}.
*
* @return this element as a {@link Number}.
* @throws UnsupportedOperationException if this element is not a {@link JsonPrimitive} or {@link
* JsonArray}, or cannot be converted to a number.
* @throws IllegalStateException if this element is of the type {@link JsonArray} but contains
* more than a single element.
*/
public Number getAsNumber() {
throw new UnsupportedOperationException(getClass().getSimpleName());
}
/**
* Convenience method to get this element as a string value.
*
* @return this element as a string value.
* @throws UnsupportedOperationException if this element is not a {@link JsonPrimitive} or {@link
* JsonArray}.
* @throws IllegalStateException if this element is of the type {@link JsonArray} but contains
* more than a single element.
*/
public String getAsString() {
throw new UnsupportedOperationException(getClass().getSimpleName());
}
/**
* Convenience method to get this element as a primitive double value.
*
* @return this element as a primitive double value.
* @throws UnsupportedOperationException if this element is not a {@link JsonPrimitive} or {@link
* JsonArray}.
* @throws NumberFormatException if the value contained is not a valid double.
* @throws IllegalStateException if this element is of the type {@link JsonArray} but contains
* more than a single element.
*/
public double getAsDouble() {
throw new UnsupportedOperationException(getClass().getSimpleName());
}
/**
* Convenience method to get this element as a primitive float value.
*
* @return this element as a primitive float value.
* @throws UnsupportedOperationException if this element is not a {@link JsonPrimitive} or {@link
* JsonArray}.
* @throws NumberFormatException if the value contained is not a valid float.
* @throws IllegalStateException if this element is of the type {@link JsonArray} but contains
* more than a single element.
*/
public float getAsFloat() {
throw new UnsupportedOperationException(getClass().getSimpleName());
}
/**
* Convenience method to get this element as a primitive long value.
*
* @return this element as a primitive long value.
* @throws UnsupportedOperationException if this element is not a {@link JsonPrimitive} or {@link
* JsonArray}.
* @throws NumberFormatException if the value contained is not a valid long.
* @throws IllegalStateException if this element is of the type {@link JsonArray} but contains
* more than a single element.
*/
public long getAsLong() {
throw new UnsupportedOperationException(getClass().getSimpleName());
}
/**
* Convenience method to get this element as a primitive integer value.
*
* @return this element as a primitive integer value.
* @throws UnsupportedOperationException if this element is not a {@link JsonPrimitive} or {@link
* JsonArray}.
* @throws NumberFormatException if the value contained is not a valid integer.
* @throws IllegalStateException if this element is of the type {@link JsonArray} but contains
* more than a single element.
*/
public int getAsInt() {
throw new UnsupportedOperationException(getClass().getSimpleName());
}
/**
* Convenience method to get this element as a primitive byte value.
*
* @return this element as a primitive byte value.
* @throws UnsupportedOperationException if this element is not a {@link JsonPrimitive} or {@link
* JsonArray}.
* @throws NumberFormatException if the value contained is not a valid byte.
* @throws IllegalStateException if this element is of the type {@link JsonArray} but contains
* more than a single element.
* @since 1.3
*/
public byte getAsByte() {
throw new UnsupportedOperationException(getClass().getSimpleName());
}
/**
* Convenience method to get the first character of the string value of this element.
*
* @return the first character of the string value.
* @throws UnsupportedOperationException if this element is not a {@link JsonPrimitive} or {@link
* JsonArray}, or if its string value is empty.
* @throws IllegalStateException if this element is of the type {@link JsonArray} but contains
* more than a single element.
* @since 1.3
* @deprecated This method is misleading, as it does not get this element as a char but rather as
* a string's first character.
*/
@Deprecated
public char getAsCharacter() {
throw new UnsupportedOperationException(getClass().getSimpleName());
}
/**
* Convenience method to get this element as a {@link BigDecimal}.
*
* @return this element as a {@link BigDecimal}.
* @throws UnsupportedOperationException if this element is not a {@link JsonPrimitive} or {@link
* JsonArray}.
* @throws NumberFormatException if this element is not a valid {@link BigDecimal}.
* @throws IllegalStateException if this element is of the type {@link JsonArray} but contains
* more than a single element.
* @since 1.2
*/
public BigDecimal getAsBigDecimal() {
throw new UnsupportedOperationException(getClass().getSimpleName());
}
/**
* Convenience method to get this element as a {@link BigInteger}.
*
* @return this element as a {@link BigInteger}.
* @throws UnsupportedOperationException if this element is not a {@link JsonPrimitive} or {@link
* JsonArray}.
* @throws NumberFormatException if this element is not a valid {@link BigInteger}.
* @throws IllegalStateException if this element is of the type {@link JsonArray} but contains
* more than a single element.
* @since 1.2
*/
public BigInteger getAsBigInteger() {
throw new UnsupportedOperationException(getClass().getSimpleName());
}
/**
* Convenience method to get this element as a primitive short value.
*
* @return this element as a primitive short value.
* @throws UnsupportedOperationException if this element is not a {@link JsonPrimitive} or {@link
* JsonArray}.
* @throws NumberFormatException if the value contained is not a valid short.
* @throws IllegalStateException if this element is of the type {@link JsonArray} but contains
* more than a single element.
*/
public short getAsShort() {
throw new UnsupportedOperationException(getClass().getSimpleName());
}
/**
* Converts this element to a JSON string.
*
* For example:
*
*
* JsonObject object = new JsonObject();
* object.add("a", JsonNull.INSTANCE);
* JsonArray array = new JsonArray();
* array.add(1);
* object.add("b", array);
*
* String json = object.toString();
* // json: {"a":null,"b":[1]}
*
*
* If this element or any nested elements contain {@link Double#NaN NaN} or {@link
* Double#isInfinite() Infinity} that value is written to JSON, even though the JSON specification
* does not permit these values.
*
* To customize formatting or to directly write to an {@link Appendable} instead of creating an
* intermediate {@code String} first, use {@link Gson#toJson(JsonElement, Appendable)
* Gson.toJson(JsonElement, ...)}.
*
*
To get the contained String value (without enclosing {@code "} and without escaping), use
* {@link #getAsString()} instead:
*
*
* JsonPrimitive jsonPrimitive = new JsonPrimitive("with \" quote");
* String json = jsonPrimitive.toString();
* // json: "with \" quote"
* String value = jsonPrimitive.getAsString();
* // value: with " quote
*
*/
@Override
public String toString() {
try {
StringWriter stringWriter = new StringWriter();
JsonWriter jsonWriter = new JsonWriter(stringWriter);
// Make writer lenient because toString() must not fail, even if for example JsonPrimitive
// contains NaN
jsonWriter.setStrictness(Strictness.LENIENT);
Streams.write(this, jsonWriter);
return stringWriter.toString();
} catch (IOException e) {
throw new AssertionError(e);
}
}
}