问题描述
@Value
@Builder(toBuilder = true)
public class Customer {
private final List<Remark> remarks;
}
当我序列化对象 objectwriter.writeValueAsstring(currentDossier)
并在我看到的 JSON 输出中打印值时,
{ "remarks" : {
"empty" : true,"lazy" : false,"async" : false,"traversableAgain" : true,"sequential" : true,"ordered" : false,"singleValued" : false,"distinct" : false,"orNull" : null,"memoized" : false
}
}
其中备注是对象内的 vavr 列表字段。
现在,如果我尝试将相同的值反序列化到对象 objectMapper.readValue(json,Customer.class)
中,则会出现错误:
com.fasterxml.jackson.databind.exc.InvalidDeFinitionException: Cannot construct instance of `io.vavr.collection.List`
(no Creators,like default construct,exist): abstract types either need to be mapped to concrete types,have custom deserializer,or contain additional type information
at [Source: (String)"{"remarks" : {
为什么在尝试反序列化时序列化的 JSON 文本不起作用?
@Test
public void mapperForVavrList() throws JsonProcessingException {
Customer cus = Customer.builder().remarks(List.empty()).build();
ObjectWriter ow = new ObjectMapper()
.writer().withDefaultPrettyPrinter();
String json1 = ow.writeValueAsstring(cus);
log.info(json1);
ObjectMapper objectMapper = new ObjectMapper();
Customer cus2 = objectMapper.readValue(json1,Customer.class);
log.info(cus2.toString());
}
Java 代码中是否还有其他方法可以以文本格式打印 vavr 对象并将其转换回 POJO?
解决方法
您可以使用 jackson 轻松地将 vavr 对象序列化/反序列化为 JSON。您需要做的是在 VavrModule
的实例上注册 ObjectMapper
:
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new VavrModule());
要获得 VavrModule
,您需要将依赖项添加到 vavr-jackson
编辑
在这里你可以找到一个完整的工作示例:
import com.fasterxml.jackson.databind.ObjectMapper;
import io.vavr.collection.List;
import io.vavr.jackson.datatype.VavrModule;
import org.apache.commons.lang3.builder.ToStringBuilder;
import java.io.IOException;
class Lol2 {
public static void main(String[] args) throws IOException {
Customer c = new Customer();
Remark r = new Remark();
r.whatever = "whatever";
c.remarks = List.of(r);
ObjectMapper ow = new ObjectMapper();
ow.registerModule(new VavrModule());
System.out.println(c);
String json = ow.writeValueAsString(c);
System.out.println(json);
Customer c2 = ow.readValue(json,Customer.class);
System.out.println(c2);
}
}
class Customer {
List<Remark> remarks;
public List<Remark> getRemarks() {
return remarks;
}
public void setRemarks(List<Remark> remarks) {
this.remarks = remarks;
}
@Override
public String toString() {
return new ToStringBuilder(this)
.append("remarks",remarks)
.toString();
}
}
class Remark {
String whatever;
public String getWhatever() {
return whatever;
}
public void setWhatever(String whatever) {
this.whatever = whatever;
}
@Override
public String toString() {
return new ToStringBuilder(this)
.append("whatever",whatever)
.toString();
}
}