Json解析工具Jackson（使用注解） .

接上一篇文章 Json解析工具Jackson（简单应用），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。

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

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

  //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 + "]";
  	}
  
  }

  
  

  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();
  		}
  	}
  
  
  }