18 Sep 2017
Java Object To Json

Here is the example of using Java jackson to convert object to json trick.

we have a class like below, pay attention to the isActive attribute.

//original class
public abstract class AbstractLookup implements ILookup {

	private Integer lookupId;
	private String description;
	private Integer sortOrder;
	private Boolean isActive;

	public AbstractLookup() {
	}
	public AbstractLookup(Integer lookupId) {
		setLookupId(lookupId);
	}
	public Integer getLookupId() {
		return lookupId;
	}
	public void setLookupId(Integer lookupId) {
		this.lookupId = lookupId;
	}
	public String getDescription() {
		return description;
	}
	public void setDescription(String description) {
		this.description = description;
	}
	public Integer getSortOrder() {
		return sortOrder;
	}
	public void setSortOrder(Integer sortOrder) {
		this.sortOrder = sortOrder;
	}
	private Boolean getIsActive() {
		return isActive;
	}
	public Boolean isActive() {
		return getIsActive() == null ? false : getIsActive().booleanValue();
	}
	public void setIsActive(Boolean isActive) {
		this.isActive = isActive;
	}
}

public PeerCode extends AbstractLookup{
	...
}

We tried to convert the PeerCode modle class to json

PeerCode peerCode = new PeerCode ();
...
ObjectMapper mapper = new ObjectMapper();
String peerCodeStr =  mapper.writerWithDefaultPrettyPrinter().writeValueAsString(peerCode);

We got the exception:

Caused by: com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "active" (class com.xxx.PeerCode), not marked as ignorable (4 known properties: "sortOrder", "isActive", "lookupId", "description"])
 at [Source: java.io.PushbackInputStream@188daa2; line: 12, column: 21] (through reference chain: com.xxxx.PeerCode["active"])
	at com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException.from(UnrecognizedPropertyException.java:51)

Because we have a method “isActive()” which is not belong to the standard model class, jackson think there is a attribute call “active”, thus it not able to match this attribute to the target class.

Two solution: https://stackoverflow.com/questions/14708386/want-to-hide-some-fields-of-an-object-that-are-being-mapped-to-json-by-jackson

use @JsonIgnoreProperties annotation

@JsonIgnoreProperties(ignoreUnknown = true)
public abstract class AbstractLookup implements ILookup {
...
}

We got the result json

{
  "PeerCode" : {
 "lookupId" : null,
 "description" : null,
 "sortOrder" : null,
 "p4pPeerGroupId" : 2,
 "active" : false
  }
}

It is not right, because isActive become active

use @JsonIgnore annotation

@JsonIgnore
public Boolean isActive() {
 return getIsActive() == null ? false : getIsActive().booleanValue();
}

We got the result json

{
  "PeerCode" : {
 "lookupId" : null,
 "description" : null,
 "sortOrder" : null,
 "p4pPeerGroupId" : 2
  }
}

The active is gone, not seems right

So we need add addition annotation to customize the name of the getIsActive method

import com.fasterxml.jackson.annotation.JsonGetter;
import com.fasterxml.jackson.annotation.JsonIgnore;
...
@JsonGetter("isActive")
private Boolean getIsActive() {
	return isActive;
}

Finally it display correct:

{
  "PeerCode" : {
    "lookupId" : null,
    "description" : null,
    "sortOrder" : null,
    "p4pPeerGroupId" : 2,
    "isActive" : true
  }
}

Final abstract class AbstractLookup

public abstract class AbstractLookup implements ILookup {

	private Integer lookupId;
	private String description;
	private Integer sortOrder;
	private Boolean isActive;

	public AbstractLookup() {
	}
	public AbstractLookup(Integer lookupId) {
		setLookupId(lookupId);
	}
	public Integer getLookupId() {
		return lookupId;
	}
	public void setLookupId(Integer lookupId) {
		this.lookupId = lookupId;
	}
	public String getDescription() {
		return description;
	}
	public void setDescription(String description) {
		this.description = description;
	}
	public Integer getSortOrder() {
		return sortOrder;
	}
	public void setSortOrder(Integer sortOrder) {
		this.sortOrder = sortOrder;
	}
	@JsonGetter("isActive")
	private Boolean getIsActive() {
		return isActive;
	}
	@JsonIgnore
	public Boolean isActive() {
		return getIsActive() == null ? false : getIsActive().booleanValue();
	}
	public void setIsActive(Boolean isActive) {
		this.isActive = isActive;
	}
}

Tips:

org.codehaus.jackson is an older version of Jackson. Jackson has moved from Codehaus to Github when releasing Jackson 2.
com.fasterxml.jackson represents the new project and package.

recommend removing org.codehaus.jackson references from your POM, re-building and looking for errors.

Til next time,
at 00:00

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The World

18 Sep 2017 Java Object To Json

Tips:

18 Sep 2017
Java Object To Json