杰克逊 + 建造者模式？

我希望 Jackson 用以下构造函数反序列化一个类:

public Clinic(String name, Address address)

反序列化第一个参数很容易，问题是 Address 被定义为:

public class Address {
private Address(Map<LocationType, String> components)
...


public static class Builder {
public Builder setCity(String value);
public Builder setCountry(String value);
public Address create();
}
}

结构如下: new Address.Builder().setCity("foo").setCountry("bar").create();

有没有办法从杰克逊那里获得键值对，以便自己构建地址？或者，有没有办法让 Jackson 使用 Builder 类本身？

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There is no support currently for builder pattern, although it has been requested quite a while ago (and finally Jira issue http://jira.codehaus.org/browse/JACKSON-469 was filed) -- it is something that may be added for 1.8 release if there is enough demand (make sure to vote at Jira!). It is a reasonable additional feature, and only delayed by amount of time developers have. But I think it would be great addition.

小开

I ended up implementing this using the @JsonDeserialize as follows:

@JsonDeserialize(using = JacksonDeserializer.class)
public class Address
{...}


@JsonCachable
static class JacksonDeserializer extends JsonDeserializer<Address>
{
@Override
public Address deserialize(JsonParser parser, DeserializationContext context)
throws IOException, JsonProcessingException
{
JsonToken token = parser.getCurrentToken();
if (token != JsonToken.START_OBJECT)
{
throw new JsonMappingException("Expected START_OBJECT: " + token, parser.getCurrentLocation());
}
token = parser.nextToken();
Builder result = new Builder();
while (token != JsonToken.END_OBJECT)
{
if (token != JsonToken.FIELD_NAME)
{
throw new JsonMappingException("Expected FIELD_NAME: " + token, parser.getCurrentLocation());
}
LocationType key = LocationType.valueOf(parser.getText());


token = parser.nextToken();
if (token != JsonToken.VALUE_STRING)
{
throw new JsonMappingException("Expected VALUE_STRING: " + token, parser.getCurrentLocation());
}
String value = parser.getText();


// Our Builder allows passing key-value pairs
// alongside the normal setter methods.
result.put(key, value);
token = parser.nextToken();
}
return result.create();
}
}
小开
最佳答案

As long as you are using Jackson 2+, then there is now built in support for this.

First you need to add this annotation to your Address class:

@JsonDeserialize(builder = Address.Builder.class)

Then you need to add this annotation to your Builder class: 

@JsonPOJOBuilder(buildMethodName = "create", withPrefix = "set")

You can skip this second annotation if you are happy to rename your Builder's create method to build, and your Builder's setters to be prefixed to with, instead of set.

Full example:

@JsonDeserialize(builder = Address.Builder.class)
public class Address
{
private Address(Map<LocationType, String> components)
...


@JsonPOJOBuilder(buildMethodName = "create", withPrefix = "set")
public static class Builder
{
public Builder setCity(String value);
public Builder setCountry(String value);
public Address create();
}
}
小开

The answer from @Rupert Madden-Abbott works. However, if you have a non-default constructor, e.g.,

Builder(String city, String country) {...}

Then you should annotate the parameters as below:

@JsonCreator
Builder(@JsonProperty("city")    String city,
@JsonProperty("country") String country) {...}
小开

A solution which was suitable for me in this case (I used "Lombok" builder annotation).

@Getter
@Builder(builderMethodName = "builder")
@NoArgsConstructor(access = AccessLevel.PRIVATE)
@AllArgsConstructor(access = AccessLevel.PRIVATE)
@JsonAutoDetect(
fieldVisibility = JsonAutoDetect.Visibility.ANY,
creatorVisibility = JsonAutoDetect.Visibility.ANY
)

I hope would be useful for u too.

小开

This worked for me: @NoArgsConstructor The only drawback of this, is that one can do = new ADTO() again. But, hey, I dont like de code police anyhow, telling me how to use someones code :-) So, use my POJO DTOS the way you like it. With or without builder. I suggest: do it with a Builder, but be my guest...

@Data
@Builder
//Dont forget this! Otherwise no Jackson serialisation possible!
@NoArgsConstructor
@AllArgsConstructor
public class ADTO {
.....
}

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