为什么我不能打开根节点并反序列化一个对象数组？ [英] Why can't I unwrap the root node and deserialize an array of objects?
问题描述
为什么我无法通过展开根节点来反序列化对象数组？
Why am I not able to deserialize an array of objects by unwrapping the root node?
import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import org.codehaus.jackson.map.DeserializationConfig;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.annotate.JsonRootName;
import org.junit.Assert;
import org.junit.Test;
public class RootNodeTest extends Assert {
@JsonRootName("customers")
public static class Customer {
public String email;
}
@Test
public void testUnwrapping() throws IOException {
String json = "{\"customers\":[{\"email\":\"hello@world.com\"},{\"email\":\"john.doe@example.com\"}]}";
ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationConfig.Feature.UNWRAP_ROOT_VALUE, true);
List<Customer> customers = Arrays.asList(mapper.readValue(json, Customer[].class));
System.out.println(customers);
}
}
我一直在挖掘杰克逊的文档，这个我可以弄清楚，但在运行它时，我收到以下错误：
I've been digging through the Jackson documentation and this is what I could figure out but upon running it, I get the following error:
A org.codehaus.jackson.map.JsonMappingException has been caught, Root name 'customers' does not match expected ('Customer[]') for type [array type, component type: [simple type, class tests.RootNodeTest$Customer]] at [Source: java.io.StringReader@49921538; line: 1, column: 2]
我想在不创建包装类的情况下完成此操作。虽然这是一个示例，但我不想仅为展开根节点创建不必要的包装类。
I would like to accomplish this without creating a wrapper class. While this is an example, I don't want to create unnecessary wrapper classes only for unwrapping the root node.
推荐答案
创建一个ObjectReader以明确配置根名称：
Create an ObjectReader to configure the root name explicitly:
@Test
public void testUnwrapping() throws IOException {
String json = "{\"customers\":[{\"email\":\"hello@world.com\"},{\"email\":\"john.doe@example.com\"}]}";
ObjectReader objectReader = mapper.reader(new TypeReference<List<Customer>>() {})
.withRootName("customers");
List<Customer> customers = objectReader.readValue(json);
assertThat(customers, contains(customer("hello@world.com"), customer("john.doe@example.com")));
}
（顺便说一下这是Jackson 2.5，你有不同的版本吗？我有DeserializationFeature而不是DeserializationConfig.Feature）
(btw this is with Jackson 2.5, do you have a different version? I have DeserializationFeature rather than DeserializationConfig.Feature)
似乎通过以这种方式使用对象阅读器，您不需要全局配置展开根值功能，也不要使用 @JsonRootName 注释。
It seems that by using an object reader in this fashion, you don't need to globally configure the "unwrap root value" feature, nor use the @JsonRootName annotation.
另请注意，您可以直接申请列表< Customer> 而不是通过数组 - 给予 ObjectMapper.reader 的类型就像
Note also that you can directly request a List<Customer> rather than going through an array- the type given to ObjectMapper.reader works just like the second parameter to ObjectMapper.readValue
这篇关于为什么我不能打开根节点并反序列化一个对象数组？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
