Fastjson处理枚举

1,891 阅读3分钟

Fastjson

这玩意儿不多说,Alibaba出品,出过几次严重的安全漏洞,但是依然很流行。这里写一下它怎么处理枚举。

<!-- https://mvnrepository.com/artifact/com.alibaba/fastjson -->
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.2.76</version>
</dependency>

序列化为name()值

默认就是,啥也不用动

import com.alibaba.fastjson.JSON;

enum Gender {
	BOY, GIRL, UNKNOW
}

class User {
	private Integer id;
	private Gender gender;
	public User() {
	}
	public User(Integer id, Gender gender) {
		super();
		this.id = id;
		this.gender = gender;
	}

	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public Gender getGender() {
		return gender;
	}

	public void setGender(Gender gender) {
		this.gender = gender;
	}
}

public class MainTest {

	public static void main(String[] args) throws Exception {
		
		// 序列化为JSON输出
		User user = new User(1, Gender.BOY);
		String jsonString = JSON.toJSONString(user); 
		System.out.println(jsonString);	// {"gender":"BOY","id":1}
		
		
		// 反序列化为对象
		user = JSON.parseObject(jsonString, User.class);
		System.out.println(user.getGender());		// BOY
	}
}

序列化为ordinal()值

全局设置

代码跟上面没有变化,就需要在开头添加一句代码,任何枚举,都会被序列化为ordinal()值

JSON.DEFAULT_GENERATE_FEATURE &= ~SerializerFeature.WriteEnumUsingName.mask;
		// 全局设置,枚举的序列化使用 ordinal()
		JSON.DEFAULT_GENERATE_FEATURE &= ~SerializerFeature.WriteEnumUsingName.mask;
		
		// 序列化为JSON输出,枚举值为 ordinal()
		User user = new User(1, Gender.BOY);
		String jsonString = JSON.toJSONString(user); 
		System.out.println(jsonString);	// {"gender":0,"id":1}
		
		
		// 反序列化为对象
		user = JSON.parseObject(jsonString, User.class);
		System.out.println(user.getGender());		// BOY

特殊设置

只想针对某一次序列化生效。只需要调用JSON.toJSONString的重载方法,添加配置就行。

public static String toJSONString(Object object, int defaultFeatures, SerializerFeature... features)
		// 序列化为JSON输出,本次把枚举值序列化为 ordinal()
		User user = new User(1, Gender.BOY);
		String jsonString = JSON.toJSONString(user, JSON.DEFAULT_GENERATE_FEATURE & ~SerializerFeature.WriteEnumUsingName.mask); 
		System.out.println(jsonString);	// {"gender":0,"id":1}
		
		
		// 反序列化为对象
		user = JSON.parseObject(jsonString, User.class);
		System.out.println(user.getGender());		// BOY

序列化为自定义属性

很多人也喜欢给枚举定义一个私有的属性,序列化为JSON时,希望以这个属性值作为value,这个时候就需要自己定义JSON的序列化和反序列化实现了。Fastjson提供了2个接口。用户控制序列化和反序列化行为,这个实在是太简单,这里不多说。看代码

  • ObjectSerializer
  • ObjectDeserializer

序列化器的定义

import java.io.IOException;
import java.lang.reflect.Type;

import com.alibaba.fastjson.serializer.JSONSerializer;
import com.alibaba.fastjson.serializer.ObjectSerializer;

public class GenderEnumSerializer implements ObjectSerializer {
	@Override
	public void write(JSONSerializer serializer, Object object, Object fieldName, Type fieldType, int features) throws IOException {
		// 强制把值转换为Gender
		Gender gender = (Gender) object;
		// 序列化为自定义的name属性,输出就行
		serializer.out.writeString(gender.getName());
	}
}

反序列化器的定义

import java.lang.reflect.Type;

import com.alibaba.fastjson.parser.DefaultJSONParser;
import com.alibaba.fastjson.parser.JSONToken;
import com.alibaba.fastjson.parser.deserializer.ObjectDeserializer;

public class GenderEnumDeserializer implements ObjectDeserializer {
	@SuppressWarnings("unchecked")
	@Override
	public <T> T deserialze(DefaultJSONParser parser, Type type, Object fieldName) {
		// 解析值为字符串
		String value = parser.parseObject(String.class);
		// 遍历所有的枚举实例
		for (Gender gender : Gender.values()) {
			if (gender.getName().equals(value)) {
				// 成功匹配,返回实例
				return (T) gender;
			}
		}
		// 没有匹配到,可以抛出异常或者返回null
		return null;
	}

	@Override
	public int getFastMatchToken() {
		// 仅仅匹配字符串类型的值
		return JSONToken.LITERAL_STRING;
	}
}

对象 & 枚举的定义

enum Gender {
	
	BOY("男"), GIRL("女"), UNKNOW("不知道");
	
	public final String name;
	
	Gender(String name) {
		this.name = name;
	}
	public String getName() {
		return name;
	}
}


class User {
	
	private Integer id;
	
	// 标识注解,指定枚举的序列化。反序列化实现类
	@JSONField(serializeUsing = GenderEnumSerializer.class, deserializeUsing = GenderEnumDeserializer.class)
	private Gender gender;

	public User() {
	}

	public User(Integer id, Gender gender) {
		super();
		this.id = id;
		this.gender = gender;
	}

	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public Gender getGender() {
		return gender;
	}

	public void setGender(Gender gender) {
		this.gender = gender;
	}
}

测试

public class MainTest {

	public static void main(String[] args) throws Exception {

		// 序列化为JSON输出,枚举值为 getName()
		User user = new User(1, Gender.UNKNOW);
		String jsonString = JSON.toJSONString(user);
		System.out.println(jsonString); // {"gender":"不知道","id":1}

		// 反序列化为对象
		user = JSON.parseObject(jsonString, User.class);
		System.out.println(user.getGender()); // UNKNOW
	}
}

最后

很显然,自定义 ObjectSerializer /ObjectDeserializer 的方式最为灵活,可以考虑抽象一个接口出来,让所有的枚举都实现接口。这样针对接口编写ObjectSerializer /ObjectDeserializer实现,就可以很好的复用了。


本文首发:springboot.io/t/topic/364…