359 lines
7.0 KiB
Markdown
359 lines
7.0 KiB
Markdown
# 0. FASTJSON 2.0介绍
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`FASTJSON v2`是`FASTJSON`项目的重要升级，目标是为下一个十年提供一个高性能的`JSON`库。通过同一套`API`，
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- 支持`JSON/JSONB`两种协议，[`JSONPath`](https://alibaba.github.io/fastjson2/jsonpath_cn) 是一等公民。
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- 支持全量解析和部分解析。
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- 支持`Java`服务端、客户端`Android`、大数据场景。
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- 支持`Kotlin`
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- 支持`JSON Schema` [https://alibaba.github.io/fastjson2/json_schema_cn](https://alibaba.github.io/fastjson2/json_schema_cn)
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- 支持`Android`
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- 支持`Graal Native-Image`
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相关文档：
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- `JSONB`格式文档：
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[https://alibaba.github.io/fastjson2/jsonb_format_cn](https://alibaba.github.io/fastjson2/jsonb_format_cn)
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- `FASTJSON v2`性能有了很大提升，具体性能数据看这里：
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[https://alibaba.github.io/fastjson2/benchmark_cn](https://alibaba.github.io/fastjson2/benchmark_cn)
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# 1. 使用准备
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## 1.1 添加依赖
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在`fastjson v2`中，`groupId`和`1.x`不一样，是`com.alibaba.fastjson2`：
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`Maven`:
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```xml
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<dependency>
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<groupId>com.alibaba.fastjson2</groupId>
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<artifactId>fastjson2</artifactId>
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<version>2.0.28</version>
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</dependency>
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```
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`Gradle`:
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```groovy
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dependencies {
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implementation 'com.alibaba.fastjson2:fastjson2:2.0.28'
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}
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```
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可以在 [maven.org](https://search.maven.org/artifact/com.alibaba.fastjson2/fastjson2) 查看最新可用的版本。
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## 1.2 其他模块
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### `Fastjson v1`兼容模块
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如果原来使用`fastjson 1.2.x`版本，可以使用兼容包，兼容包不能保证100%兼容，请仔细测试验证，发现问题请及时反馈。
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`Maven`:
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```xml
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<dependency>
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<groupId>com.alibaba</groupId>
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<artifactId>fastjson</artifactId>
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<version>2.0.28</version>
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</dependency>
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```
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`Gradle`:
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```groovy
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dependencies {
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implementation 'com.alibaba:fastjson:2.0.28'
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}
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```
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### `Fastjson Kotlin`集成模块
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如果项目使用`Kotlin`，可以使用`fastjson-kotlin`模块，使用方式上采用`kotlin`的特性。
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`Maven`:
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```xml
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<dependency>
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<groupId>com.alibaba.fastjson2</groupId>
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<artifactId>fastjson2-kotlin</artifactId>
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<version>2.0.28</version>
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</dependency>
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```
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`Gradle`:
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```kotlin
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dependencies {
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implementation("com.alibaba.fastjson2:fastjson2-kotlin:2.0.28")
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}
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```
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### `Fastjson Extension`扩展模块
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如果项目使用`SpringFramework`等框架，可以使用`fastjson-extension`模块，使用方式参考 [SpringFramework Support](https://alibaba.github.io/fastjson2/spring_support_cn)。
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`Maven`:
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```xml
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<dependency>
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<groupId>com.alibaba.fastjson2</groupId>
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<artifactId>fastjson2-extension</artifactId>
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<version>2.0.28</version>
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</dependency>
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```
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`Gradle`:
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```groovy
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dependencies {
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implementation 'com.alibaba.fastjson2:fastjson2-extension:2.0.28'
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}
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```
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# 2 简单使用
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在`fastjson v2`中，`package`和`1.x`不一样，是`com.alibaba.fastjson2`。如果你之前用的是`fastjson1`，大多数情况直接更包名就即可。
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### 2.1 将`JSON`解析为`JSONObject`
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`Java`:
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```java
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String text = "...";
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JSONObject data = JSON.parseObject(text);
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byte[] bytes = ...;
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JSONObject data = JSON.parseObject(bytes);
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```
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`Kotlin`:
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```kotlin
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import com.alibaba.fastjson2.*
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val text = ... // String
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val data = text.parseObject()
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val bytes = ... // ByteArray
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val data = bytes.parseObject() // JSONObject
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```
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### 2.2 将`JSON`解析为`JSONArray`
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`Java`:
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```java
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String text = "...";
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JSONArray data = JSON.parseArray(text);
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```
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`Kotlin`:
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```kotlin
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import com.alibaba.fastjson2.*
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val text = ... // String
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val data = text.parseArray() // JSONArray
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```
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### 2.3 将`JSON`解析为`Java`对象
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`Java`:
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```java
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String text = "...";
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User data = JSON.parseObject(text, User.class);
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```
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`Kotlin`:
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```kotlin
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import com.alibaba.fastjson2.*
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val text = ... // String
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val data = text.to<User>() // User
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val data = text.parseObject<User>() // User
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```
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### 2.4 将`Java`对象序列化为`JSON`
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`Java`:
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```java
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Object data = "...";
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String text = JSON.toJSONString(data);
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byte[] text = JSON.toJSONBytes(data);
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```
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`Kotlin`:
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```kotlin
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import com.alibaba.fastjson2.*
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val data = ... // Any
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val text = text.toJSONString() // String
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val bytes = text.toJSONByteArray() // ByteArray
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```
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### 2.5 使用`JSONObject`、`JSONArray`
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#### 2.5.1 获取简单属性
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```java
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String text = "{\"id\": 2,\"name\": \"fastjson2\"}";
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JSONObject obj = JSON.parseObject(text);
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int id = obj.getIntValue("id");
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String name = obj.getString("name");
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```
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```java
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String text = "[2, \"fastjson2\"]";
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JSONArray array = JSON.parseArray(text);
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int id = array.getIntValue(0);
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String name = array.getString(1);
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```
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#### 2.5.2 读取`JavaBean`
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`Java`:
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```java
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JSONArray array = ...
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JSONObject obj = ...
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User user = array.getObject(0, User.class);
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User user = obj.getObject("key", User.class);
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```
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`Kotlin`:
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```kotlin
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val array = ... // JSONArray
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val obj = ... // JSONObject
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val user = array.getObject<User>(0)
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val user = obj.getObject<User>("key")
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```
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#### 2.5.3 转为`JavaBean`
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`Java`:
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```java
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JSONArray array = ...
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JSONObject obj = ...
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User user = obj.toJavaObject(User.class);
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List<User> users = array.toJavaList(User.class);
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```
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`Kotlin`:
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```kotlin
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val array = ... // JSONArray
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val obj = ... // JSONObject
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val user = obj.toObject<User>() // User
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val users = array.toList<User>() // List<User>
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```
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### 2.6 将`JavaBean`对象序列化为`JSON`
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`Java`:
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```java
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class User {
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public int id;
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public String name;
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}
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User user = new User();
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user.id = 2;
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user.name = "FastJson2";
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String text = JSON.toJSONString(user);
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byte[] bytes = JSON.toJSONBytes(user);
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```
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`Kotlin`:
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```kotlin
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class User(
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var id: Int,
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var name: String
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)
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val user = User()
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user.id = 2
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user.name = "FastJson2"
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val text = user.toJSONString() // String
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val bytes = user.toJSONByteArray() // ByteArray
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```
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序列化结果:
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```json
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{
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"id" : 2,
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"name" : "FastJson2"
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}
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```
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# 3. 进阶使用
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### 3.1 使用`JSONB`
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#### 3.1.1 将`JavaBean`对象序列化`JSONB`
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```java
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User user = ...;
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byte[] bytes = JSONB.toBytes(user);
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byte[] bytes = JSONB.toBytes(user, JSONWriter.Feature.BeanToArray);
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```
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#### 3.1.2 将`JSONB`数据解析为`JavaBean`
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```java
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byte[] bytes = ...
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User user = JSONB.parseObject(bytes, User.class);
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User user = JSONB.parseObject(bytes, User.class, JSONReader.Feature.SupportBeanArrayMapping);
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```
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### 3.2 使用`JSONPath`
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#### 3.2.1 使用`JSONPath`读取部分数据
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```java
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String text = ...;
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JSONPath path = JSONPath.of("$.id"); // 缓存起来重复使用能提升性能
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JSONReader parser = JSONReader.of(text);
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Object result = path.extract(parser);
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```
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#### 3.2.2 使用`JSONPath`读取部分`byte[]`的数据
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```java
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byte[] bytes = ...;
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JSONPath path = JSONPath.of("$.id"); // 缓存起来重复使用能提升性能
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JSONReader parser = JSONReader.of(bytes);
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Object result = path.extract(parser);
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```
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#### 3.2.3 使用`JSONPath`读取部分`byte[]`的数据
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```java
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byte[] bytes = ...;
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JSONPath path = JSONPath.of("$.id"); // 缓存起来重复使用能提升性能
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JSONReader parser = JSONReader.ofJSONB(bytes); // 注意这里使用ofJSONB方法
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Object result = path.extract(parser);
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```
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