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Many novices are not very clear about how to use @ JacksonInject and @ JsonAlias annotations. In order to help you solve this problem, the following editor will explain it in detail. People with this need can come and learn. I hope you can learn something.

Let's continue to show you how to use @ JacksonInject annotations and @ JsonAlias annotations during JSON deserialization

1. @ JacksonInject comments

We often have such requirements when using the JSON format for deserialization. We have obtained a data object in JSON format from the client or other sources, which contains several properties. But when we deserialize a JSON string, we need to add some default data to it, such as:

Response time of responseTime data, which can be assigned to the current time

The operator of data deserialization, assigning values to the current user of the system, etc.

The data returned to us by the client itself does not carry this additional information, so we can use JacksonInject annotations to add this additional information when the JSON string is deserialized into an object. Here is how to use JacksonInject

[@ Data] (https://my.oschina.net/difrik)public class PlayerStar {private String name; private Integer age; private String [] hobbies; / / hobby, array private List friends; / / friend private Map salary; / / annual income Map @ JacksonInject ("responseTime") / / Note here private LocalDateTime responseTime;}

Let's test the deserialization process. It is important to note that the jsonInString below does not carry responseTime information. We injected it into the java object during deserialization.

[@ Test] (https://my.oschina.net/azibug)void testJSON2Object () throws IOException {/ / assign responseTime the current value InjectableValues.Std iv = new InjectableValues.Std (); iv.addValue ("responseTime", LocalDateTime.now ()); ObjectMapper mapper = new ObjectMapper (); mapper.setInjectableValues (iv) / / to deserialize JSON strings into java objects String jsonInString = "{\" name\ ":\" Jordan\ ",\" age\ ": 45,\" hobbies\ ": [\" Golf\ ",\" Baseball\ "}"; PlayerStar jordan = mapper.readValue (jsonInString, PlayerStar.class); System.out.println (jordan);}

In the final deserialization result, the output of the toString () method of the java object is as follows. You can see that there is an extra responseTime assignment attribute with a value of the current time.

PlayerStar (name= Jordan, age=45, hobbies= [Golf, Baseball], friends=null, salary=null, responseTime=2020-09-22T06:41:09.192) II. Data injection according to data type type

In the code above, the JSON string is deserialized into an object, injected using the method of the property id

@ JacksonInject ("responseTime") / / Note that responseTime is attribute id private LocalDateTime responseTime; InjectableValues.Std iv = new InjectableValues.Std (); iv.addValue ("responseTime", LocalDateTime.now ()); / / notice that responseTime is attribute id, and this should be unified.

In addition to injecting data according to the attribute id, you can also use the java type data type for data injection. This method is not convenient to use in a java class when multiple member variable data types are duplicated, such as defining multiple LocalDateTime member variables. Therefore, it is recommended that you use the method of attribute id for injection data injection.

@ JacksonInject private LocalDateTime responseTime; InjectableValues.Std iv = new InjectableValues.Std (); iv.addValue (LocalDateTime.class, LocalDateTime.now ()); / / Note here LocalDateTime.class III, @ JsonAlias notes

When we are in the development process, the PlayerStar class we defined (above) may contain the name attribute in the v1.0 version, but we use to find that the word name is too generic and is a system keyword in many places; we hope that in the v2.0 version, this member variable will be renamed starName, or playerName. But we don't want users to abandon the v1.0 interface. In other words, we want to be multi-version compatible, and the JSON string sent by the client can be name, playerName, or starName. What are we supposed to do? The answer is to use @ JsonAlias annotations

@ Datapublic class PlayerStar {@ JsonAlias ({"starName", "playerName"}) private String name

The following three types of JSON format data can be correctly deserialized into PlayerStar objects and assigned values to name member variables

String jsonInString = "{\" name\ ":\" Jordan\ ",\" age\ ": 45,\" hobbies\ ": [\" Golf\ ",\" Baseball\ "}"; String jsonInString = "{\" starName\ ":\" Jordan\ ",\" age\ ": 45,\" hobbies\ ": [\" Golf\ ",\" Baseball\ "]}" String jsonInString = "{\" playerName\ ":\" Jordan\ ",\" age\ ": 45,\" hobbies\ ": [\" Golf\ ",\" Baseball\ "}". Is it helpful for you to read the above? If you want to know more about the relevant knowledge or read more related articles, please follow the industry information channel, thank you for your support.

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