Jackson Core framework Frequently Asked Questions and Best Practice
Jackson Core is a popular Java library that is used to process the serialization and derivativeization of JSON data.It provides powerful and flexible functions, but there are some common problems and best practices to pay attention to.
Question 1: How to sequence the java object into a JSON string?
Using the Jackson Core Library can easily convert Java objects into JSON string.The following is a simple sample code:
```java
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
public class SerializationExample {
public static void main(String[] args) {
ObjectMapper objectMapper = new ObjectMapper();
// Create a serialized Java object
User user = new User("John Doe", 30);
try {
// Convert java objects to json string
String jsonString = objectMapper.writeValueAsString(user);
System.out.println(jsonString);
} catch (JsonProcessingException e) {
e.printStackTrace();
}
}
}
class User {
private String name;
private int age;
// Construct function, Getters and Setters omit
User(String name, int age) {
this.name = name;
this.age = age;
}
}
```
This example creates a simple Java object called User, and serializes it into a JSON string through the WriteValueasstring () method of ObjectMapper.In this case, the output result will be `{" name ":" John Doe "," Age ": 30}`.
Question 2: How to turn the JSON string to the Java object?
Similarly, the Jackson Core library makes the back serialized JSON string is relatively simple to Java objects.The following is an example code:
```java
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
public class DeserializationExample {
public static void main(String[] args) {
ObjectMapper objectMapper = new ObjectMapper();
String jsonString = "{\"name\":\"John Doe\",\"age\":30}";
try {
// Convert json string to Java object
User user = objectMapper.readValue(jsonString, User.class);
System.out.println(user.getName());
System.out.println(user.getAge());
} catch (JsonProcessingException e) {
e.printStackTrace();
}
}
}
class User {
private String name;
private int age;
// Construct function, Getters and Setters omit
User() {
// The default constructor must exist and use it for deepertine
}
}
```
In this example, a JSON string is first created, and then it turns its backflow into a User object through ObjectMapper's readvalue () method.Finally, the attribute value of the recovery object can be printed.
Question 3: How to deal with the NULL value in JSON?
When processing the NULL value in JSON, the default behavior of Jackson Core is to convert the NULL value to the default value of the Java object.If you need to view the NULL value as an effective value, you can use the @JSONINCLUDE annotation for configuration.The example is as follows:
```java
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
@JsonInclude(JsonInclude.Include.NON_NULL)
public class NullHandlingExample {
public static void main(String[] args) {
ObjectMapper objectMapper = new ObjectMapper();
User user = new User(null, 30);
try {
// Convert java objects to json string
String jsonString = objectMapper.writeValueAsString(user);
System.out.println(jsonString);
} catch (JsonProcessingException e) {
e.printStackTrace();
}
}
}
class User {
@JsonInclude(JsonInclude.Include.NON_NULL)
private String name;
private int age;
// Construct function, Getters and Setters omit
User(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
}
```
In this example, the name property of the User object is marked as @JSONINCLUDE (JSONINCLUDE.INCLUDE.NON_NULL), which means that when named is null, it will not be included in the generated json string.
Best Practice 1: Use @JSONFORMAT Note Control Date Format
When the date attributes in the Java object need to be serialized into a string in a specific format, you can use the @JSONFORMAT annotation.The following is an example code:
```java
import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.Date;
public class DateSerializationExample {
public static void main(String[] args) {
ObjectMapper objectMapper = new ObjectMapper();
Event event = new Event("Event Title", new Date());
try {
// Convert java objects to json string
String jsonString = objectMapper.writeValueAsString(event);
System.out.println(jsonString);
} catch (JsonProcessingException e) {
e.printStackTrace();
}
}
}
class Event {
private String title;
@JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd HH:mm:ss")
private Date startDate;
// Construct function, Getters and Setters omit
Event(String title, Date startDate) {
this.title = title;
this.startDate = startDate;
}
}
```
In this example, the StartDate property of the Event object is marked as @jsonformat (shape = jsonformat.shape.string, Pattern = "Yyyy-MM-DD HH: SS"), which means that it is serialized as a JSON string as a JSON stringAt this time, the date will be displayed in the format of "YYYYY-MM-DD HH: MM: SS".
Best Practice II: Use custom serialization and desertation
The Jackson Core library allows customized serialization and derivativeization logic to more finely control the conversion process between JSON and Java objects.The following is an example code:
```java
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
import java.io.IOException;
public class CustomSerializationExample {
public static void main(String[] args) {
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.registerModule(new CustomModule());
User user = new User("John Doe", 30);
try {
// Convert java objects to json string
String jsonString = objectMapper.writeValueAsString(user);
System.out.println(jsonString);
} catch (JsonProcessingException e) {
e.printStackTrace();
}
}
}
class CustomSerializer extends JsonSerializer<String> {
@Override
public void serialize(String value, JsonGenerator gen, SerializerProvider serializers) throws IOException {
String reversedString = new StringBuilder(value).reverse().toString();
gen.writeString(reversedString);
}
}
class CustomDeserializer extends StdDeserializer<String> {
protected CustomDeserializer() {
super(String.class);
}
@Override
public String deserialize(JsonParser p, com.fasterxml.jackson.databind.DeserializationContext ctxt) throws IOException {
String originalString = p.readValueAs(String.class);
return new StringBuilder(originalString).reverse().toString();
}
}
class CustomModule extends com.fasterxml.jackson.databind.Module {
@Override
public String getModuleName() {
return "CustomModule";
}
@Override
public Version version() {
return new Version(1, 0, 0, null, null, null);
}
@Override
public void setupModule(Module.SetupContext context) {
context.addSerializer(String.class, new CustomSerializer());
context.addDeserializer(String.class, new CustomDeserializer());
}
}
class User {
private String name;
private int age;
// Construct function, Getters and Setters omit
User(String name, int age) {
this.name = name;
this.age = age;
}
}
```
In this example, we define a self -defined CustomSerializer and CustomDeserializer and registered them in CustomModule.CustomSerializer reverses the string, and CustomDeserializer reverses the reversed string again.When using ObjectMapper to sequence the User object to the JSON string, the name property will be processed by the logic of the CustomSerializer first.
Summarize:
The Jackson Core framework provides powerful and flexible functions, which can easily process the serialization and derivativeization of JSON data.This article introduces some common questions and best practices, hoping to help readers help readers when using Jackson Core.
