问题场景
在使用java的Long类型过程中,当这个Long类型数值超过 1^0+1^1+1^2+...1^58的范围后就会引发精度丢失, 详见JS[IEEE754规范](https://en.wikipedia.org/wiki/IEEE_754)
常见的现象就是比如:1000967854800048128,通过js转换成Number类型成为了:1000967854800048100, 由此会引发一系列问题,比如当年著名的爱国者导弹.
因为精度缺失造成问题,大多数情况发生在前后端交互过程中,那么下面就分别说说处理方法
普通场景的处理方法
简单的处理方法，jackson,gson等json工具包已经包含了Long类型处理方法了,基本上都是转String.
gson处理方法
GsonBuilder builder = new GsonBuilder();
//默认将所有的Long转换成String
builder.setLongSerializationPolicy(LongSerializationPolicy.STRING);
jackson处理方法
ObjectMapper objectMapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addSerializer(Long.class, ToStringSerializer.instance);
module.addSerializer(Long.TYPE, ToStringSerializer.instance);
高级场景处理
为了避免将其他无需转换成String的Long类型转换,这里提供一个高级的用法，
思路很简单就是定义一个Id类型,通过实现Id类型的序列化和反序列化功能即可进行实现.
下面就用Gson和jackson来演示
核心代码
//Gson
GsonBuilder builder = new GsonBuilder();
builder.registerTypeAdapter(Id.class, (JsonSerializer<Id>) (src, typeOfSrc, context) ->
new JsonPrimitive(src.getVal()));
builder.registerTypeAdapter(Id.class, (JsonDeserializer<Id>) (json, typeOfT, context) ->
new Id(json.getAsLong()));
Gson gson = builder.create();
User user = new User();
user.setUserId(new Id(11111L));
user.setUserName("youkale.github.io");
String s = gson.toJson(user);
System.out.println(s);
User user1 = gson.fromJson(s, User.class);
System.out.println("gson " + user1);
//Jackson
ObjectMapper objectMapper = new ObjectMapper();
SimpleModule module = new SimpleModule();
module.addSerializer(Id.class, new IdJacksonSerializer(Id.class));
module.addDeserializer(Id.class, new IdJacksonDeserializer(Id.class));
objectMapper.registerModule(module);
String s1 = objectMapper.writeValueAsString(user);
System.out.println(s1);
User user2 = objectMapper.readValue(s1, User.class);
System.out.println("jackson " + user2);
定义类User
public static class User {
private Id userId;
private String userName;
public Id getUserId() {
return userId;
}
public void setUserId(Id userId) {
this.userId = userId;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
@Override
public String toString() {
return "User{" +
"userId=" + userId +
", userName='" + userName + '\'' +
'}';
}
}
定义Id类
public static class Id {
private final Long val;
public Long getVal() {
return val;
}
public Id(Long val) {
this.val = val;
}
@Override
public String toString() {
return String.valueOf(val);
}
}
jackson序列反序列实现
public static class IdJacksonDeserializer extends StdDeserializer<Id> {
public IdJacksonDeserializer(Class<?> vc) {
super(vc);
}
@Override
public Id deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
return new Id(p.getValueAsLong());
}
}
public static class IdJacksonSerializer extends StdSerializer<Id> {
public IdJacksonSerializer(Class<Id> t) {
super(t);
}
@Override
public void serialize(Id value, JsonGenerator gen, SerializerProvider provider) throws IOException {
gen.writeString(String.valueOf(value.getVal()));
}
}
总结
从Gson和jackson的API看出这类的功能老早就由大神们想到了,有时候总在感叹,自己多渺小.
