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，将一个Date类型转化成指定类型字符串。

public class JsonDoubleSerialize extends JsonSerializer<Double> {

private DecimalFormat df = new DecimalFormat("##.000");

@Override
public void serialize(Double value, JsonGenerator jgen,
SerializerProvider provider) throws IOException,
JsonProcessingException {

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

/**
* 把Date类型序列化成指定合适的字符串
*/
public class JsonDateSerialize extends JsonSerializer<Date> {
@Override
public void serialize(Date date, JsonGenerator jgen,
SerializerProvider provider)
throws IOException, JsonProcessingException {
String formattedDate = "";
if (date != null) {
//把日期序列化成yyyy-MM-dd格式的字符串
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
formattedDate = simpleDateFormat.format(date);
}
jgen.writeString(formattedDate);
}
}

@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

/**
* 将一个字符串反序列化成一个Date类型
*/
public class JsonDateDeserialize extends JsonDeserializer<Date> {

@Override
public Date deserialize(JsonParser jp, DeserializationContext ctxt)
throws IOException, JsonProcessingException {
//拿到的是"yyyy-MM-dd"形式的字符串，现在要在json反序列化的时候转化成Date类型
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
String date = jp.getText();
if (date == null || date.trim().length() == 0) {
return null;
}
try {
return format.parse(date);
} catch (Exception e) {

}
return null;
}
}

完整例子

//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;
@JsonSerialize(using = JsonDateSerialize.class)
@JsonDeserialize(using = JsonDateDeserialize.class)
private Date birthday;
private String word;
@JsonSerialize(using = JsonDoubleSerialize.class)
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;
}

public void setBirthday(Date birthday) {
this.birthday = birthday;
}

public String getWord() {
return word;
}

public void setWord(String word) {
this.word = word;
}

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 + "]";
}

}

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("zhangsan", 25, true, new Date(), "coder",
2500.0);
try {
String string = mapper.writeValueAsString(person);
//{"name":"zhangsan","age":25,"sex":true,"birthday":"2016-12-03 22:02:23","salary":"2500.000"}
System.out.println(string);
} 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 {
String string = "{\"name\":\"zhangsan\",\"age\":25,\"sex\":true,\"birthday\":\"2016-12-03 22:02:23\",\"word\":\"coder\",\"salary\":\"2500.000\"}";
Person person = mapper.readValue(string, Person.class);
//Person [name=zhangsan, age=25, sex=true, birthday=Sat Dec 03 00:00:00 CST 2016, word=null, salary=2500.0]
System.out.println(person.toString());
} catch (JsonParseException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}

refer：http://blog.csdn.net/nomousewch/article/details/8955796