JSON和POJO转换 -- fasterxml

本篇介绍fasterxml的json库，可以用于POJO互换Json payload。类似的库有.Net的Newtonsoft。fasterxml用到两个lib：jackson-databind和jackson-core。

POJO不能含有构造器。下面代码首先用Customer的实例产生json，再读入json转换成cusomer实例。以下是json结果：
{"customerId":555,"address":{"city":"Seattle","state":null}}

MyJsonHelper.java:
public class MyJsonHelper {

public void toObject() throws JsonParseException, JsonMappingException, IOException {
Customer customer = mapper.readValue(new File("test.json"), Customer.class);
System.out.println(customer.getAddress());
}

public void toJson() throws JsonGenerationException, JsonMappingException, IOException {

Customer customer = new Customer();
Address address = new Address();
address.setCity("Seattle");
customer.setCustomerId(555);
customer.setAddress(address);

//Object to JSON in file
mapper.writeValue(new File("test.json"), customer);

//Object to JSON in String
String jsonInString = mapper.writeValueAsString(customer);
System.out.println(jsonInString);
}

private ObjectMapper mapper = new ObjectMapper();
}

Customer.java:
public class Customer {

private int customerId = 4;
private Address address;

public void setCustomerId(int custid){
this.customerId = custid;
}

public int getCustomerId(){
return customerId;
}

public void setAddress(Address address){
this.address = address;
}

public Address getAddress(){
return address;
}
}

Address.java:
public class Address {

private String city;
private String state;

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

public String getCity(){
return city;
}

public void setState(String state){
this.state = state;
}

public String getState(){
return state;
}

@Override public boolean equals(Object other) { return EqualsBuilder.reflectionEquals(this, other); }

@Override
public String toString()
{
   return ToStringBuilder.reflectionToString(this); 
}
}

//Exclude fields
EqualsBuilder(this, other, new String[]{"id", "name"})

Annotation:

@JsonInclude(JsonInclude.Include.NON_EMPTY)
表示只有非空域才会进入json文件，如结果变为
{"customerId":555,"address":{"city":"Seattle"}}

之前提过不能用构造器，如果要用，就要加入@JsonCreator和@JsonProperty

@JsonInclude(JsonInclude.Include.NON_EMPTY)
public class Address {

@JsonCreator
public Address(@JsonProperty("city") String city, @JsonProperty("state") String state){
this.state = state;
this.city = city;
}

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

@JsonProperty
public String getCity(){
return city;
}

public void setState(String state){
this.state = state;
}

@JsonProperty
public String getState(){
return state;
}

private String city;
private String state;
}

fasterxml + AutoValue

@AutoValue
@JsonDeserialize(builder = AutoValue_Account.Builder.class)
public abstract class Account {
@JsonProperty("name")
public abstract String getName();

@JsonProperty("accountNumber")
public abstract String getAccountNumber();

public static Builder builder(){
return new AutoValue_Account.Builder();
}

@AutoValue.Builder
public abstract static class Builder {
@JsonProperty("name")
   public abstract Builder setName(String value);

   @JsonProperty("accountNumber")
   public abstract Builder setAccountNumber(String value);
   public abstract Account build();
}
}

@JsonIgnore 不加入Json生成中
ref:
fasterxml例子