Master FastJSON 2.0: Maven Setup, Core APIs, and Advanced JSONPath Techniques

FastJSON 2.0 Overview

FastJSON 2.0 is a major upgrade of the FastJSON project, delivering a high‑performance JSON library for the next decade. It supports both JSON and JSONB protocols with a unified API, treats JSONPath as a first‑class citizen, and runs on Java servers, Android clients, and big‑data scenarios.

1. Preparation

1.1 Maven Dependency

<dependency>
  <groupId>com.alibaba.fastjson2</groupId>
  <artifactId>fastjson2</artifactId>
  <version>2.0.1</version>
</dependency>

Repository: https://repo1.maven.org/maven2/com/alibaba/fastjson2/fastjson2/

1.2 Compatibility with FastJSON 1.x

If you are upgrading from 1.2.x, you can use the compatibility artifact (groupId com.alibaba, artifactId fastjson, version 2.0.1). Compatibility is not 100 % guaranteed; thorough testing is required.

<dependency>
  <groupId>com.alibaba</groupId>
  <artifactId>fastjson</artifactId>
  <version>2.0.1</version>
</dependency>

2. Core Classes and Methods

All classes are now under the package com.alibaba.fastjson2. The most frequently used classes are shown below.

package com.alibaba.fastjson2;

class JSON {
    // Parse a JSON string into a JSONObject
    static JSONObject parseObject(String str);
    // Parse a JSON string into a JSONArray
    static JSONArray parseArray(String str);
    // Parse UTF‑8 bytes into a Java object of the given type
    static <T> T parseObject(byte[] utf8Bytes, Class<T> objectClass);
    // Serialize a Java object to a JSON string
    static String toJSONString(Object object);
    // Serialize a Java object to UTF‑8 bytes
    static byte[] toJSONBytes(Object object);
}

class JSONB {
    // Parse JSONB bytes into a Java object
    static <T> T parseObject(byte[] jsonbBytes, Class<T> objectClass);
    // Serialize a Java object to JSONB bytes
    static byte[] toBytes(Object object);
}

class JSONObject {
    Object get(String key);
    int getIntValue(String key);
    Integer getInteger(String key);
    long getLongValue(String key);
    Long getLong(String key);
    <T> T getObject(String key, Class<T> objectClass);
    <T> T toJavaObject(Class<T> objectClass);
}

class JSONArray {
    Object get(int index);
    int getIntValue(int index);
    Integer getInteger(int index);
    long getLongValue(int index);
    Long getLong(int index);
    <T> T getObject(int index, Class<T> objectClass);
}

class JSONPath {
    // Create a JSONPath instance
    static JSONPath of(String path);
    // Partial parsing using a JSONReader
    Object extract(JSONReader jsonReader);
    // Evaluate a path against a Java object
    Object eval(Object rootObject);
}

class JSONReader {
    static JSONReader of(String str);
    static JSONReader of(byte[] utf8Bytes);
    static JSONReader of(char[] chars);
    static JSONReader ofJSONB(byte[] jsonbBytes);
}

3. Reading JSON Objects

String str = "{\"id\":123}";
JSONObject jsonObject = JSON.parseObject(str);
int id = jsonObject.getIntValue("id");

String arrStr = "[\"id\",123]";
JSONArray jsonArray = JSON.parseArray(arrStr);
String name = jsonArray.getString(0);
int id2 = jsonArray.getIntValue(1);

4. Serializing Java Beans

4.1 To JSON String

class Product {
    public int id;
    public String name;
}

Product product = new Product();
product.id = 1001;
product.name = "DataWorks";
String json = JSON.toJSONString(product);
// Result: {"id":1001,"name":"DataWorks"}

String jsonArray = JSON.toJSONString(product, JSONWriter.Feature.BeanToArray);
// Result: [1001,"DataWorks"]

4.2 To UTF‑8 Bytes

byte[] utf8JSONBytes = JSON.toJSONBytes(product);

4.3 To JSONB Bytes

byte[] jsonbBytes = JSONB.toBytes(product);
byte[] jsonbArrayBytes = JSONB.toBytes(product, JSONWriter.Feature.BeanToArray);

5. Deserializing Java Beans

5.1 From JSON String

String str = "{\"id\":123}";
Product product = JSON.parseObject(str, Product.class);

5.2 From UTF‑8 Bytes

byte[] utf8Bytes = "{\"id\":123}".getBytes(StandardCharsets.UTF_8);
Product product = JSON.parseObject(utf8Bytes, Product.class);

5.3 From JSONB Bytes

byte[] jsonbBytes = ...;
Product product = JSONB.parseObject(jsonbBytes, Product.class);
// With bean‑array mapping support
Product product2 = JSONB.parseObject(jsonbBytes, Product.class, JSONReader.Feature.SupportBeanArrayMapping);

6. Using JSONPath

6.1 Extract from a JSON string

String str = ...;
JSONPath path = JSONPath.of("$.id"); // cache for reuse
JSONReader parser = JSONReader.of(str);
Object result = path.extract(parser);

6.2 Extract from UTF‑8 bytes

byte[] utf8Bytes = ...;
JSONPath path = JSONPath.of("$.id");
JSONReader parser = JSONReader.of(utf8Bytes);
Object result = path.extract(parser);

6.3 Extract from JSONB bytes

byte[] jsonbBytes = ...;
JSONPath path = JSONPath.of("$.id");
JSONReader parser = JSONReader.ofJSONB(jsonbBytes); // note the ofJSONB method
Object result = path.extract(parser);