Json解析工具Jackson（使用注解）

jackson在实际应用中给我们提供了一系列注解，提高了开发的灵活性，下面介绍一下最常用的一些注解

@JsonIgnoreProperties

此注解是类注解，作用是json序列化时将java bean中的一些属性忽略掉，序列化和反序列化都受影响。

@JsonIgnore

此注解用于属性或者方法上（最好是属性上），作用和上面的@JsonIgnoreProperties一样。

@JsonFormat

此注解用于属性或者方法上（最好是属性上），可以方便的把Date类型直接转化为我们想要的模式，比如@JsonFormat(pattern = "yyyy-MM-dd HH-mm-ss")

@JsonSerialize

此注解用于属性或者getter方法上，用于在序列化时嵌入我们自定义的代码，比如序列化一个double时在其后面限制两位小数点。

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public class CustomDoubleSerialize extends JsonSerializer<Double> {

private DecimalFormat df = new DecimalFormat("##.00");

@Override

public void serialize(Double value, JsonGenerator jgen,

SerializerProvider provider) throws IOException,

JsonProcessingException {

jgen.writeString(df.format(value));

}

}

@JsonDeserialize

此注解用于属性或者setter方法上，用于在反序列化时可以嵌入我们自定义的代码，类似于上面的@JsonSerialize

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public class CustomDateDeserialize extends JsonDeserializer<Date> {

private SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

@Override

public Date deserialize(JsonParser jp, DeserializationContext ctxt)

throws IOException, JsonProcessingException {

Date date = null;

try {

date = sdf.parse(jp.getText());

} catch (ParseException e) {

e.printStackTrace();

}

return date;

}

}

完整例子

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//表示序列化时忽略的属性

@JsonIgnoreProperties(value = { "word" })

public class Person {

private String name;

private int age;

private boolean sex;

private Date birthday;

private String word;

private double salary;

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 boolean isSex() {

return sex;

}

public void setSex(boolean sex) {

this.sex = sex;

}

public Date getBirthday() {

return birthday;

}

// 反序列化一个固定格式的Date

@JsonDeserialize(using = CustomDateDeserialize.class)

public void setBirthday(Date birthday) {

this.birthday = birthday;

}

public String getWord() {

return word;

}

public void setWord(String word) {

this.word = word;

}

// 序列化指定格式的double格式

@JsonSerialize(using = CustomDoubleSerialize.class)

public double getSalary() {

return salary;

}

public void setSalary(double salary) {

this.salary = salary;

}

public Person(String name, int age) {

this.name = name;

this.age = age;

}

public Person(String name, int age, boolean sex, Date birthday,

String word, double salary) {

super();

this.name = name;

this.age = age;

this.sex = sex;

this.birthday = birthday;

this.word = word;

this.salary = salary;

}

public Person() {

}

@Override

public String toString() {

return "Person [name=" + name + ", age=" + age + ", sex=" + sex

+ ", birthday=" + birthday + ", word=" + word + ", salary="

+ salary + "]";

}

}

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public class Demo {

public static void main(String[] args) {

writeJsonObject();

// readJsonObject();

}

// 直接写入一个对象(所谓序列化)

public static void writeJsonObject() {

ObjectMapper mapper = new ObjectMapper();

Person person = new Person("nomouse", 25, true, new Date(), "程序员",

2500.0);

try {

mapper.writeValue(new File("c:/person.json"), person);

} catch (JsonGenerationException e) {

e.printStackTrace();

} catch (JsonMappingException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

}

// 直接将一个json转化为对象（所谓反序列化）

public static void readJsonObject() {

ObjectMapper mapper = new ObjectMapper();

try {

Person person = mapper.readValue(new File("c:/person.json"),

Person.class);

System.out.println(person.toString());

} catch (JsonParseException e) {

e.printStackTrace();

} catch (JsonMappingException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

}

}