我正在使用Jackson示例，并且在使用不可变类和接口进行反序列化时遇到一些麻烦。
以下是我的代码：
package com.art.starter.jackson_starter;
import java.io.IOException;
import java.io.StringReader;
import java.io.StringWriter;
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
/** * Hello world! * */ public class App {
public static void main( String[] args ) throws JsonGenerationException, JsonMappingException, IOException
{
System.out.println( "Hello World!" );
AddressImpl.AddressBuilder builder = new AddressImpl.AddressBuilder();
NameImpl.Builder nameBuilder = new NameImpl.Builder();
UserImpl.Builder userBuilder = new UserImpl.Builder();
Name name = nameBuilder.first("FirstName")
.last("LastName")
.build();
Address address = builder.setCity("TestCity")
.setCountry("TestCountry")
.setState("PA")
.setStreet("TestAddress")
.setZip(123)
.build();
User user = userBuilder.address(address)
.gender(User.Gender.MALE)
.isVerified(true)
.userImage(new byte[5])
.build();
System.out.println(address);
System.out.println(name);
System.out.println(user);
StringWriter sw = new StringWriter();
ObjectMapper mapper = new ObjectMapper();
mapper.writeValue(sw, user);
System.out.println(sw);
StringReader sr = new StringReader("{\"address\":{\"state\":\"PA\",\"country\":\"TestCountry\",\"street\":\"TestAddress\",\"city\":\"TestCity\",\"zip\":123},\"verified\":true,\"gender\":\"MALE\",\"userImage\":\"AAAAAAA=\"}");
/*
This line throws the Exception
*/
User user2 = mapper.readValue(sr, UserImpl.class);
System.out.println(user2);
} }
package com.art.starter.jackson_starter;
import java.util.Arrays;
import org.codehaus.jackson.annotate.JsonCreator;
import org.codehaus.jackson.annotate.JsonProperty;
public final class UserImpl implements User
{
private final Address address;
private final Gender gender;
private final byte[] userImage;
private final boolean isVerified;
public static class Builder
{
private Address address;
private Gender gender;
// private Name name;
private byte[] userImage;
private boolean isVerified;
public Builder address(Address address)
{
this.address = address;
return this;
}
public Builder gender(Gender gender)
{
this.gender = gender;
return this;
}
// public Builder name(Name name)
// {
// this.name = name;
// return this;
// }
public Builder userImage(byte[] userImage)
{
this.userImage = userImage;
return this;
}
public Builder isVerified(boolean isVerified)
{
this.isVerified = isVerified;
return this;
}
public UserImpl build()
{
return new UserImpl(address, gender, userImage, isVerified);
}
}
@JsonCreator
public UserImpl(@JsonProperty("address") Address address, @JsonProperty("gender") Gender gender, @JsonProperty("userImage") byte[] userImage,
@JsonProperty("verified") boolean isVerified)
{
super();
this.address = address;
this.gender = gender;
this.userImage = userImage;
this.isVerified = isVerified;
}
public Address getAddress()
{
return address;
}
public Gender getGender()
{
return gender;
}
public byte[] getUserImage()
{
return userImage;
}
public boolean isVerified()
{
return isVerified;
}
@Override
public String toString()
{
StringBuilder builder2 = new StringBuilder();
builder2.append("UserImpl [address=");
builder2.append(address);
builder2.append(", gender=");
builder2.append(gender);
builder2.append(", isVerified=");
builder2.append(isVerified);
builder2.append(", name=");
builder2.append(", userImage=");
builder2.append(Arrays.toString(userImage));
builder2.append("]");
return builder2.toString();
}
}
package com.art.starter.jackson_starter;
import org.codehaus.jackson.annotate.JsonCreator;
import org.codehaus.jackson.annotate.JsonProperty;
public final class AddressImpl implements Address
{
private final String city;
private final String country;
private final String street;
private final String state;
private final int zip;
public static class AddressBuilder
{
private String city;
private String country;
private String street;
private String state;
private int zip;
public AddressBuilder setCity(String city)
{
this.city = city;
return this;
}
public AddressBuilder setCountry(String country)
{
this.country = country;
return this;
}
public AddressBuilder setStreet(String street)
{
this.street = street;
return this;
}
public AddressBuilder setState(String state)
{
this.state = state;
return this;
}
public AddressBuilder setZip(int zip)
{
this.zip = zip;
return this;
}
public AddressImpl build()
{
return new AddressImpl(city, country, street, state, zip);
}
}
@JsonCreator
public AddressImpl(@JsonProperty("city") String city, @JsonProperty("country") String country, @JsonProperty("street") String street,
@JsonProperty("state") String state, @JsonProperty("zip") int zip)
{
this.city = city;
this.country = country;
this.street = street;
this.state = state;
this.zip = zip;
}
public String getCity()
{
return city;
}
public String getCountry()
{
return country;
}
public String getStreet()
{
return street;
}
public String getState()
{
return state;
}
public int getZip()
{
return zip;
}
@Override
public String toString()
{
StringBuilder builder = new StringBuilder();
builder.append("AddressImpl [city=");
builder.append(city);
builder.append(", country=");
builder.append(country);
builder.append(", state=");
builder.append(state);
builder.append(", street=");
builder.append(street);
builder.append(", zip=");
builder.append(zip);
builder.append("]");
return builder.toString();
}
}
问题似乎与地址有关。我得到了这个例外：
Exception in thread "main" org.codehaus.jackson.map.JsonMappingException: Can not construct instance of com.art.starter.jackson_starter.Address, problem: abstract types can only be instantiated with additional type information
at [Source: java.io.StringReader@785f8172; line: 1, column: 2]
at org.codehaus.jackson.map.JsonMappingException.from(JsonMappingException.java:163)
at org.codehaus.jackson.map.deser.StdDeserializationContext.instantiationException(StdDeserializationContext.java:212)
at org.codehaus.jackson.map.deser.AbstractDeserializer.deserialize(AbstractDeserializer.java:97)
at org.codehaus.jackson.map.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:230)
at org.codehaus.jackson.map.deser.BeanDeserializer._deserializeUsingPropertyBased(BeanDeserializer.java:595)
at org.codehaus.jackson.map.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:472)
at org.codehaus.jackson.map.deser.BeanDeserializer.deserialize(BeanDeserializer.java:350)
at org.codehaus.jackson.map.ObjectMapper._readMapAndClose(ObjectMapper.java:2391)
at org.codehaus.jackson.map.ObjectMapper.readValue(ObjectMapper.java:1614)
at com.art.starter.jackson_starter.App.main(App.java:56)
我确信这是因为杰克逊无法解析Address，这是AddressImpl的一个接口，这是一个具体的实现。我一直在浏览文档并查看了一些关于@JsonDeserialize（as = AddressImpl.class）的文章，但它没有用。所以我很难过。有没有人得到这个工作，它甚至支持？
如果我将Address替换为AddressImpl类中的UserImpl，它就像冠军一样。
答案 0 :(得分：20)
万一你还没有看到它，这里有blog entry讨论使用不可变对象和杰克逊。
但是你绝对可以通过将@JsonDeserialize(as=AddressImpl.class);添加到Address.java接口（直接或使用混合），或者将其添加到字段或属性来使用{{1}}。需要注意的一点是，对于反序列化，它必须位于您使用的访问器旁边; setter如果你有一个，如果没有，在field旁边。访问者之间尚未共享注释;所以例如将它添加到'getter'是行不通的。
Jackson 1.8最终还允许注册抽象到具体类型（有关详细信息，请参阅http://jira.codehaus.org/browse/JACKSON-464），这可能是表明'AddressImpl'将用于'地址'的最佳选择。