【Spring Boot丨（11 ）】json的集成

**Spring Boot与JSON的集成**

JSON（JavaScript Object Notation）是一种轻量级的数据交换格式，广泛用于Web服务、移动应用程序等场景中。Spring Boot提供了对JSON的支持，使得开发者能够方便地将Java对象转换为JSON数据，并且可以使用JSON来传递数据。

**1. JSON的基本概念**

JSON是一种文本格式，用于表示JavaScript中的对象和数组。它由一系列的键值对组成，每个键值对之间用逗号分隔。例如：

json{
 "name": "John",
 "age":30,
 "city": "New York"
}

**2. Spring Boot与JSON的集成**

Spring Boot提供了一个名为`ObjectMapper`的类，用于将Java对象转换为JSON数据。我们可以使用`@JsonFormat`注解来指定JSON的格式。

### 示例代码

javaimport com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.databind.ObjectMapper;

public class User {
 private String name;
 @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "yyyy-MM-dd")
 private int age;
 private String city;

 public User(String name, int age, String city) {
 this.name = name;
 this.age = age;
 this.city = city;
 }

 public String getName() {
 return name;
 }

 public void setName(String name) {
 this.name = name;
 }

 public int getAge() {
 return age;
 }

 public void setAge(int age) {
 this.age = age;
 }

 public String getCity() {
 return city;
 }

 public void setCity(String city) {
 this.city = city;
 }
}

public class Main {
 public static void main(String[] args) throws Exception {
 User user = new User("John",30, "New York");
 ObjectMapper mapper = new ObjectMapper();
 String json = mapper.writeValueAsString(user);
 System.out.println(json);
 }
}

在上面的示例中，我们定义了一个`User`类，包含三个属性：`name`、`age`和`city`。我们使用`@JsonFormat`注解来指定JSON的格式。

### JSON的读取Spring Boot提供了一个名为`ObjectMapper`的类，用于将JSON数据转换为Java对象。我们可以使用`readValue()`方法来读取JSON数据。

javaimport com.fasterxml.jackson.databind.ObjectMapper;

public class Main {
 public static void main(String[] args) throws Exception {
 String json = "{"name":"John","age":30,"city":"New York"}";
 ObjectMapper mapper = new ObjectMapper();
 User user = mapper.readValue(json, User.class);
 System.out.println(user.getName());
 System.out.println(user.getAge());
 System.out.println(user.getCity());
 }
}

在上面的示例中，我们使用`readValue()`方法来读取JSON数据，并将其转换为一个`User`对象。

**3. JSON的序列化和反序列化**

Spring Boot提供了对JSON的序列化和反序列化支持。我们可以使用`ObjectMapper`类来实现这些功能。

### 示例代码

javaimport com.fasterxml.jackson.databind.ObjectMapper;

public class User {
 private String name;
 private int age;
 private String city;

 public User(String name, int age, String city) {
 this.name = name;
 this.age = age;
 this.city = city;
 }

 public String getName() {
 return name;
 }

 public void setName(String name) {
 this.name = name;
 }

 public int getAge() {
 return age;
 }

 public void setAge(int age) {
 this.age = age;
 }

 public String getCity() {
 return city;
 }

 public void setCity(String city) {
 this.city = city;
 }
}

public class Main {
 public static void main(String[] args) throws Exception {
 User user = new User("John",30, "New York");
 ObjectMapper mapper = new ObjectMapper();
 String json = mapper.writeValueAsString(user);
 System.out.println(json);

 User user2 = mapper.readValue(json, User.class);
 System.out.println(user2.getName());
 System.out.println(user2.getAge());
 System.out.println(user2.getCity());
 }
}

在上面的示例中，我们使用`ObjectMapper`类来实现JSON的序列化和反序列化。

**4. JSON的验证**

Spring Boot提供了对JSON的验证支持。我们可以使用`@Valid`注解来指定JSON的验证规则。

### 示例代码

javaimport javax.validation.constraints.NotBlank;

public class User {
 @NotBlank(message = "name cannot be blank")
 private String name;
 private int age;
 private String city;

 public User(String name, int age, String city) {
 this.name = name;
 this.age = age;
 this.city = city;
 }

 public String getName() {
 return name;
 }

 public void setName(String name) {
 this.name = name;
 }

 public int getAge() {
 return age;
 }

 public void setAge(int age) {
 this.age = age;
 }

 public String getCity() {
 return city;
 }

 public void setCity(String city) {
 this.city = city;
 }
}

public class Main {
 public static void main(String[] args) throws Exception {
 User user = new User("John",30, "New York");
 ObjectMapper mapper = new ObjectMapper();
 String json = mapper.writeValueAsString(user);
 System.out.println(json);

 try {
 User user2 = mapper.readValue(json, User.class);
 System.out.println(user2.getName());
 System.out.println(user2.getAge());
 System.out.println(user2.getCity());
 } catch (Exception e) {
 System.out.println(e.getMessage());
 }
 }
}

在上面的示例中，我们使用`@Valid`注解来指定JSON的验证规则。

**5. JSON的过滤**

Spring Boot提供了对JSON的过滤支持。我们可以使用`ObjectMapper`类来实现JSON的过滤。

### 示例代码

javaimport com.fasterxml.jackson.databind.ObjectMapper;

public class User {
 private String name;
 private int age;
 private String city;

 public User(String name, int age, String city) {
 this.name = name;
 this.age = age;
 this.city = city;
 }

 public String getName() {
 return name;
 }

 public void setName(String name) {
 this.name = name;
 }

 public int getAge() {
 return age;
 }

 public void setAge(int age) {
 this.age = age;
 }

 public String getCity() {
 return city;
 }

 public void setCity(String city) {
 this.city = city;
 }
}

public class Main {
 public static void main(String[] args) throws Exception {
 User user = new User("John",30, "New York");
 ObjectMapper mapper = new ObjectMapper();
 String json = mapper.writeValueAsString(user);
 System.out.println(json);

 JsonFilter filter = new JsonFilter() {
 @Override public boolean isIncludeProperty(String propertyName) {
 return !propertyName.equals("age");
 }
 };

 String filteredJson = mapper.writeValueAsString(user, filter);
 System.out.println(filteredJson);
 }
}

在上面的示例中，我们使用`ObjectMapper`类来实现JSON的过滤。

**6. JSON的排序**

Spring Boot提供了对JSON的排序支持。我们可以使用`@JsonPropertyOrder`注解来指定JSON的排序规则。

### 示例代码

javaimport com.fasterxml.jackson.annotation.JsonPropertyOrder;

public class User {
 private String name;
 @JsonPropertyOrder("age")
 private int age;
 private String city;

 public User(String name, int age, String city) {
 this.name = name;
 this.age = age;
 this.city = city;
 }

 public String getName() {
 return name;
 }

 public void setName(String name) {
 this.name = name;
 }

 public int getAge() {
 return age;
 }

 public void setAge(int age) {
 this.age = age;
 }

 public String getCity() {
 return city;
 }

 public void setCity(String city) {
 this.city = city;
 }
}

public class Main {
 public static void main(String[] args) throws Exception {
 User user = new User("John",30, "New York");
 ObjectMapper mapper = new ObjectMapper();
 String json = mapper.writeValueAsString(user);
 System.out.println(json);

 try {
 User user2 = mapper.readValue(json, User.class);
 System.out.println(user2.getName());
 System.out.println(user2.getAge());
 System.out.println(user2.getCity());
 } catch (Exception e) {
 System.out.println(e.getMessage());
 }
 }
}

在上面的示例中，我们使用`@JsonPropertyOrder`注解来指定JSON的排序规则。

**7. JSON的转换**

Spring Boot提供了对JSON的转换支持。我们