1. Overview
1.概述
This quick article is focused on how to use the @JsonComponent annotation in Spring Boot.
这篇快速文章主要介绍如何在Spring Boot中使用@JsonComponent注解。
The annotation allows us to expose an annotated class to be a Jackson serializer and/or deserializer without the need to add it to the ObjectMapper manually.
该注解允许我们将一个注解类暴露为Jackson的序列化器和/或反序列化器，而不需要手动将其添加到ObjectMapper。
This is part of the core Spring Boot module, so there are no additional dependencies required in a plain Spring Boot application.
这是Spring Boot核心模块的一部分，所以在普通的Spring Boot应用程序中不需要额外的依赖。
2. Serialization
2.序列化
Let’s start with the following User object containing a favorite color:
让我们从下面的User对象开始，该对象包含一个喜欢的颜色。
public class User {
private Color favoriteColor;
// standard getters/constructors
}
If we serialize this object using Jackson with default settings we get:
如果我们用Jackson的默认设置来序列化这个对象，我们会得到。
{
"favoriteColor": {
"red": 0.9411764740943909,
"green": 0.9725490212440491,
"blue": 1.0,
"opacity": 1.0,
"opaque": true,
"hue": 208.00000000000003,
"saturation": 0.05882352590560913,
"brightness": 1.0
}
}
We can make the JSON a lot more condensed and readable by just printing the RGB values – for example, to be used in CSS.
我们可以通过直接打印RGB值来使JSON变得更加凝练和可读–例如，在CSS中使用。
To this extent, we just have to create a class that implements JsonSerializer:
在这种情况下，我们只需要创建一个实现JsonSerializer的类。
@JsonComponent
public class UserJsonSerializer extends JsonSerializer<User> {
@Override
public void serialize(User user, JsonGenerator jsonGenerator,
SerializerProvider serializerProvider) throws IOException,
JsonProcessingException {
jsonGenerator.writeStartObject();
jsonGenerator.writeStringField(
"favoriteColor",
getColorAsWebColor(user.getFavoriteColor()));
jsonGenerator.writeEndObject();
}
private static String getColorAsWebColor(Color color) {
int r = (int) Math.round(color.getRed() * 255.0);
int g = (int) Math.round(color.getGreen() * 255.0);
int b = (int) Math.round(color.getBlue() * 255.0);
return String.format("#%02x%02x%02x", r, g, b);
}
}
With this serializer, the resulting JSON has been reduced to:
有了这个序列化器，产生的JSON已经被减少到。
{"favoriteColor":"#f0f8ff"}
Due to the @JsonComponent annotation, the serializer is registered in the Jackson ObjectMapper in the Spring Boot application. We can test this with the following JUnit test:
由于@JsonComponent注解，序列化器被注册在Spring Boot应用程序的Jackson ObjectMapper中。我们可以通过以下JUnit测试来测试。
@JsonTest
@RunWith(SpringRunner.class)
public class UserJsonSerializerTest {
@Autowired
private ObjectMapper objectMapper;
@Test
public void testSerialization() throws JsonProcessingException {
User user = new User(Color.ALICEBLUE);
String json = objectMapper.writeValueAsString(user);
assertEquals("{\"favoriteColor\":\"#f0f8ff\"}", json);
}
}
3. Deserialization
3.反序列化
Continuing with the same example, we can write a deserializer that will turn the web color String into a JavaFX Color object:
继续同一个例子，我们可以写一个反序列化器，将网页颜色String变成一个JavaFX颜色对象。
@JsonComponent
public class UserJsonDeserializer extends JsonDeserializer<User> {
@Override
public User deserialize(JsonParser jsonParser,
DeserializationContext deserializationContext) throws IOException,
JsonProcessingException {
TreeNode treeNode = jsonParser.getCodec().readTree(jsonParser);
TextNode favoriteColor
= (TextNode) treeNode.get("favoriteColor");
return new User(Color.web(favoriteColor.asText()));
}
}
Let’s test the new deserializer and make sure everything works as expected:
让我们测试一下新的反序列化器，确保一切按预期工作。
@JsonTest
@RunWith(SpringRunner.class)
public class UserJsonDeserializerTest {
@Autowired
private ObjectMapper objectMapper;
@Test
public void testDeserialize() throws IOException {
String json = "{\"favoriteColor\":\"#f0f8ff\"}"
User user = objectMapper.readValue(json, User.class);
assertEquals(Color.ALICEBLUE, user.getFavoriteColor());
}
}
4. Serializer and Deserializer in One Class
4.序列化器和反序列化器在一个类中
When desired, we can connect the serializer and the deserializer in one class by using two inner classes and adding the @JsonComponent on the enclosing class:
当需要时，我们可以通过使用两个内部类并在包围类上添加@JsonComponent，在一个类中连接串行器和反串行器。
@JsonComponent
public class UserCombinedSerializer {
public static class UserJsonSerializer
extends JsonSerializer<User> {
@Override
public void serialize(User user, JsonGenerator jsonGenerator,
SerializerProvider serializerProvider) throws IOException,
JsonProcessingException {
jsonGenerator.writeStartObject();
jsonGenerator.writeStringField(
"favoriteColor", getColorAsWebColor(user.getFavoriteColor()));
jsonGenerator.writeEndObject();
}
private static String getColorAsWebColor(Color color) {
int r = (int) Math.round(color.getRed() * 255.0);
int g = (int) Math.round(color.getGreen() * 255.0);
int b = (int) Math.round(color.getBlue() * 255.0);
return String.format("#%02x%02x%02x", r, g, b);
}
}
public static class UserJsonDeserializer
extends JsonDeserializer<User> {
@Override
public User deserialize(JsonParser jsonParser,
DeserializationContext deserializationContext)
throws IOException, JsonProcessingException {
TreeNode treeNode = jsonParser.getCodec().readTree(jsonParser);
TextNode favoriteColor = (TextNode) treeNode.get(
"favoriteColor");
return new User(Color.web(favoriteColor.asText()));
}
}
}
5. Conclusion
5.结论
This quick tutorial showed how to quickly add a Jackson serializer/deserializer in a Spring Boot application by leveraging component scanning with the @JsonComponent annotation.
这个快速教程展示了如何通过利用带有@JsonComponent注解的组件扫描，在Spring Boot应用程序中快速添加Jackson序列化器/解串器。
The code snippets can be found over on GitHub.
这些代码片段可以在GitHub上找到over。