利用jackson-databind，复杂对象对象和json数据互转

如果简单对象，那么转换的方式比较多，这里指的复杂对象，是指对象里面存在cycle引用，比如：

/**
* @author ding
*
*/
@Entity
@Table(name = "service")
public class ServicePO implements Serializable{

private static final long serialVersionUID = -6546556665143282079L;

@Id
@Column(name="service_pk")
@GeneratedValue(generator = "mcid")
@GenericGenerator(name="mcid",strategy="uuid2")
private String pk;

//包含的API
@JsonManagedReference(value="service-api")
@OneToMany(cascade={CascadeType.PERSIST,CascadeType.MERGE,CascadeType.REFRESH,CascadeType.REMOVE}, mappedBy = "servicePO", orphanRemoval = true)
private List<ApiPO> apiPOs;

......

//此处略去其他属性

}

/**
* @author ding
*/
@Entity
@Table(name = "link_api_info")
public class ApiPO implements Serializable{

private static final long serialVersionUID = 7083439085753069767L;
@Id
@Column(name="api_pk")
@GeneratedValue(generator = "mcid")
@GenericGenerator(name="mcid",strategy="uuid2")
private String pk;

//服务
@ManyToOne(cascade = CascadeType.REFRESH)
@JsonBackReference(value="service-api")
@JoinColumn(name = "service_pk")
private ServicePO servicePO;
......

//此处略去其他属性

}

ServicePO 一对多ApiPO ，两个对象互相引用，虽然有json注解，但是一般的手动json转换不管用，下面就是解决方案~~

首先引入依赖：

<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.jaxrs/jackson-jaxrs-json-provider -->
<dependency>
<groupId>com.fasterxml.jackson.jaxrs</groupId>
<artifactId>jackson-jaxrs-json-provider</artifactId>
<version>2.8.0</version>
</dependency>

object转换为json：

JsonGenerator jsonGenerator = null;
ObjectMapper objectMapper = null;
String dd1 = "";
try (ByteArrayOutputStream byt = new ByteArrayOutputStream();){
objectMapper = new ObjectMapper();
jsonGenerator = objectMapper.getJsonFactory().createJsonGenerator(byt, JsonEncoding.UTF8);
jsonGenerator.useDefaultPrettyPrinter();
objectMapper.writeValue(jsonGenerator, servicePO);
byt.flush();
dd1 = new String(byt.toByteArray(), "utf-8");
} catch (IOException e) {
logger.info("servicePO对象转json失败:"+e.getMessage());
}
JSONObject dd = JSONObject.fromObject(dd1);

jsonToObject：

String service = serPoJson;

if(service != null && !"".equals(service)){
try {
ObjectMapper objectMapper = new ObjectMapper();
servicePO = objectMapper.readValue(service, ServicePO.class);
} catch (IOException e) {
}
}