I am trying to understand Jackson and have to ask you one thing about it.
In the example below I have two classes. One of them - object to be converted to JSON, another - main method.
I know that Jackson needs default constructor but decided to experiment. I have two constructors.
So the question is - why is my output {"name":"Lion"} and int value can not be seen at all?
public class Lion extends AbstractCat {
int age;
public String name;
public Lion(int age, String name) {
this.age = age;
this.name = name;
}
public Lion() {};
}
public class Var {
public static void main(String[] args) throws IOException, JAXBException {
Lion lion = new Lion(32,"Lion");
System.out.println(converToJSON(lion));
}
public static String converToJSON(Object o) {
ObjectMapper objectMapper = new ObjectMapper();
StringWriter stringWriter = new StringWriter();
try {
objectMapper.writeValue(stringWriter,o);
} catch (IOException e) {
e.printStackTrace();
}
return stringWriter.toString();
}
}
Jackson ignores age, because it is private. Either you make age public or add a public getter method (i.e. public int getAge() { return age; }). The latter is usually the prefered variant as public fields are exposing your classes internals.
Here is my Code :
public class SearchByLambda {
private Map<String,Consumer<Person>> searchCritertiaHolder = new HashMap<String,Consumer<Person>>();
private static final String AGED = "aged";
public SearchByLambda(){
searchCritertiaHolder.put(AGED, (Person p)-> {p.filterAgedPerson(p);} );
}
private Consumer<Person> getFilter(String personType){
return searchCritertiaHolder.get(personType);
}
public static void main(String[] args) {
SearchByLambda searchUsage = new SearchByLambda();
Person p = new Person(59,"shailesh");
Person p1 = new Person(58,"ganesh");
searchUsage.getFilter(AGED).accept(p);
searchUsage.getFilter(AGED).accept(p1);
Person.printAgedPersons();
}
}
class Person{
private static List<Person> agedPersons = new ArrayList<>();
private int age;
private String name;
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Person(int age,String name){
this.age = age;
this.name = name;
}
public void filterAgedPerson(Person person){
if(person.getAge() > 58){
agedPersons.add(person);
}
}
public static void printAgedPersons(){
for(Person person : agedPersons){
System.out.println(person.getName());
}
}
}
When I replace following Lambda expression
searchCritertiaHolder.put(AGED, (Person p)-> {p.filterAgedPerson(p);});
with
searchCritertiaHolder.put(AGED, Person::filterAgedPerson);
it gives me compilation error. I am using java 8 and and compiling through eclipse. Why is this so? Why cannot I assign method reference for instance method of any arbitrary object to consumer functional interface?
Your definition of filterAgedPerson takes a Person as an argument, even though it is not a static method. It doesn't need to, and it shouldn't if you want to use it as a Consumer<Person>. What you are ending up with is something compatible with BiConsumer<Person, Person>.
It might help to think of it this way: method references to non-static methods always take an "extra" argument which is used as this.
The easiest way for you to fix this with your current code structure is to modify the filterAgedPerson method to not take a Person as an argument
public void filterAgedPerson() {
if (this.getAge() > 58) {
agedPersons.add(person);
}
}
As an aside, you might want to also consider making your filters Predicate<Person> instead of Consumer<Person> and moving the results handling elsewhere. This will give you more flexibility as things get more complicated.
I am returning an array of results with my json Objects, and I am trying to use my customObjectResponse class to pull out each of the fields within each of the objects... the problem it is expecting an object so how do I edit my class to allow it to take in an array of object to be able to then call the fields of each object... I am confused as to what needs to be added:
Here is a response example of what is being passed to be used:
[
{
itemId: 'dfsdfsdf343434',
name: 'tests',
picture: '6976-7jv8h5.jpg',
description: 'testy.',
dateUpdated: 1395101819,
}
]
Here is my response Object Class:
public class ObjResponse{
private String itemId;
private String name;
private String picture;
private String description;
private String location;
private int dateUpdated;
private String msg;
//gridview constructor
public ObjResponse(String picture) {
this.picture = picture;
}
//public constructor
public ObjResponse() {
}
public String getItemId() {
return itemId;
}
public void setItemId(String itemId) {
this.itemId = itemId;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPicture() {
return picture;
}
public void setPicture(String picture) {
this.picture = picture;
}
public String getLocation() {
return location;
}
public void setLocation(String location) {
this.location = location;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
public int getDateUpdated() {
return dateUpdated;
}
public void setDateUpdated(int dateUpdated) {
this.dateUpdated = dateUpdated;
}
public String getMsg() {
return msg;
}
}
what I am trying, but is not working, even if I separate the classes into their own files:
Data passed in:
items: [{obj1: "A", obj2: ["c", "d"]}, {etc...}]
public class Response {
public class List<Custom> {
private List<Custom> items;
}
public class Custom {
private String obj1;
private List<Obj2> obj2;
}
public Class Obj2 {
private String letters;
}
}
I ended up just calling in the callback a list of the customObject and it did the job...
new Callback<List<ObjResponse>>() {
I originally had trouble getting an idea of how the OP solved his problem but, after days of debugging I have finally figured out how to solve this issue.
So you essentially have data in the format like so (JSON Array of JSON Objects):
[
{
...
}
]
Your class that models the data and contains the getter and setter methods are nothing more than your typical POJO.
public class Person implements Serializable {
#SerializedName("Exact format of your json field name goes here")
private String firstName;
// Getters and Setters....
}
In your interface that contains your RESTful annotations you want to convert your call from:
Before:
public interface APInterface {
#GET("SOME URL TO YOUR JSON ARRAY")
Call<Person>(...)
}
After:
public interface APInterface {
#GET("SOME URL TO YOUR JSON ARRAY")
Call<List<Person>>(...)
}
In your android activity you want to convert all calls in the form of Call<Person> to Call<List<Person>>
Finally when making the initial asynchronous request call, you will want to convert your callbacks like so.
call.enqueue(new Callback<List<Person>>() {
#Override
public void onResponse(Call<List<Person>> call, Response<List<Person>> response) {
if(response.isSuccessful()){
List<Person> person = response.body();
// Can iterate through list and grab Getters from POJO
for(Person p: person){...}
} else {
// Error response...
}
}
#Override
public void onFailure(Call<List<Person>> call, Throwable t) {...}
});
Hope this helps others whom are lost from the accepted answer above.
This can also work by just passing an array of response objects. So if this is your response object:
public class CustomUserResponse {
public String firstName;
public String lastName;
...
}
You can use related syntax, depending on how you use the callbacks. Such as:
new Callback<CustomUserResponse[]>(){
#Override
public void success(CustomUserResponse[] customUserResponses, Response rawResponse) {
}
#Override
public void failure(RetrofitError error) {
}
};
OR
public class GetUserCommand implements Callback<CustomUserResponse[]> { ...
Put simply, in every place where you normally replace T with a response class, replace it with an array, instead as in CustomUserResponse[].
NOTE: to avoid confusing errors, be sure to also use an array in the Retrofit interface definition:
#POST ( "/users" )
public void listUsers(#Body GetUsersRequest request, Callback<CustomUserResponse[]> callback);
You could try something like this
JSONObject jsonObject = new JSONObject(<your JSON string result>);
JSONArray jsonArray = jsonObject.getJSONArray();
//use GSON to parse
if (jsonArray != null) {
Gson gson = new Gson();
ObjResponse[] objResponse = gson.fromJson(jsonArray.toString(), ObjResponse[].class);
List<ObjResponse> objResponseList = Arrays.asList(objResponse);
}
This should definitely work.
I am trying to serialize the below ArrayList of GAccount objects using Jackson library with following code:
List<Gaccount> gAccounts;
ObjectMapper mapper=new ObjectMapper();
json=mapper.writeValueAsString(gAccounts);
However, I have noticed that only Id and Name fields are serialized but not properties. Sorry, but I am new to Jackson library. Do I have to manually serialize that field ?
package in.co.madhur.ganalyticsdashclock;
import java.util.ArrayList;
import java.util.List;
public class GAccount
{
private String Id;
private String Name;
private List<GProperty> properties=new ArrayList<GProperty>();
public GAccount(String Id, String Name)
{
this.Id=Id;
this.Name=Name;
}
public String getName()
{
return Name;
}
public void setName(String name)
{
Name = name;
}
public String getId()
{
return Id;
}
public void setId(String id)
{
Id = id;
}
List<GProperty> getProperties()
{
return properties;
}
void setProperties(List<GProperty> properties)
{
this.properties = properties;
}
#Override
public String toString()
{
return Name;
}
}
The default visibility is to use all public getter methods and all public properties. If you make the getter this:
public List<GProperty> getProperties()
it should work.
You could also change the auto-detection defaults, but it's overkill here. See http://www.cowtowncoder.com/blog/archives/2011/02/entry_443.html for more info.
I am using jackson 2.9.0. The default visibility is always 'false' to all the members. In this case, we alway need to use a different visibility, otherwise the result json string will be empty. Here is the code extracted from JsonAutoDetect
public boolean isVisible(Member m) {
switch(this) {
case ANY:
return true;
...
case PUBLIC_ONLY:
return Modifier.isPublic(m.getModifiers());
default:
return false;
}
}
Recently I've started hearing about "POJOs" (Plain Old Java Objects). I googled it, but still don't understand the concept well. Can anyone give me a clear description of a POJO?
Consider a class "Person" with variables "id, name, address, salary" -- how would I create a POJO for this scenario? Is the code below a POJO?
public class Person {
//variables
People people = new People();
private int id;
private String name;
private String address;
private int salary;
public int getId() {
return id;
}
public String getName() {
return name;
}
public String getAddress() {
return address;
}
public int getSalary() {
return salary;
}
public void setId() {
this.id = id;
}
public void setName() {
this.name = name;
}
public void setAddress() {
this.address = address;
}
public void setSalary() {
this.salary = salary;
}
}
A POJO is just a plain, old Java Bean with the restrictions removed. Java Beans must meet the following requirements:
Default no-arg constructor
Follow the Bean convention of getFoo (or isFoo for booleans) and setFoo methods for a mutable attribute named foo; leave off the setFoo if foo is immutable.
Must implement java.io.Serializable
POJO does not mandate any of these. It's just what the name says: an object that compiles under JDK can be considered a Plain Old Java Object. No app server, no base classes, no interfaces required to use.
The acronym POJO was a reaction against EJB 2.0, which required several interfaces, extended base classes, and lots of methods just to do simple things. Some people, Rod Johnson and Martin Fowler among them, rebelled against the complexity and sought a way to implement enterprise scale solutions without having to write EJBs.
Martin Fowler coined a new acronym.
Rod Johnson wrote "J2EE Without EJBs", wrote Spring, influenced EJB enough so version 3.1 looks a great deal like Spring and Hibernate, and got a sweet IPO from VMWare out of it.
Here's an example that you can wrap your head around:
public class MyFirstPojo
{
private String name;
public static void main(String [] args)
{
for (String arg : args)
{
MyFirstPojo pojo = new MyFirstPojo(arg); // Here's how you create a POJO
System.out.println(pojo);
}
}
public MyFirstPojo(String name)
{
this.name = name;
}
public String getName() { return this.name; }
public String toString() { return this.name; }
}
POJO:- POJO is a Java object not bound by any restriction other than those forced by the Java Language Specification.
Properties of POJO
All properties must be public setter and getter methods
All instance variables should be private
Should not Extend prespecified classes.
Should not Implement prespecified interfaces.
Should not contain prespecified annotations.
It may not have any argument constructors
Example of POJO
public class POJO {
private String value;
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
}
A POJO is a Plain Old Java Object.
From the wikipedia article I linked to:
In computing software, POJO is an
acronym for Plain Old Java Object. The
name is used to emphasize that a given
object is an ordinary Java Object, not
a special object, and in particular
not an Enterprise JavaBean
Your class appears to already be a POJO.
POJO class acts as a bean which is used to set and get the value.
public class Data
{
private int id;
private String deptname;
private String date;
private String name;
private String mdate;
private String mname;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getDeptname() {
return deptname;
}
public void setDeptname(String deptname) {
this.deptname = deptname;
}
public String getDate() {
return date;
}
public void setDate(String date) {
this.date = date;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getMdate() {
return mdate;
}
public void setMdate(String mdate) {
this.mdate = mdate;
}
public String getMname() {
return mname;
}
public void setMname(String mname) {
this.mname = mname;
}
}
When you aren't doing anything to make your class particularly designed to work with a given framework, ORM, or other system that needs a special sort of class, you have a Plain Old Java Object, or POJO.
Ironically, one of the reasons for coining the term is that people were avoiding them in cases where they were sensible and some people concluded that this was because they didn't have a fancy name. Ironic, because your question demonstrates that the approach worked.
Compare the older POD "Plain Old Data" to mean a C++ class that doesn't do anything a C struct couldn't do (more or less, non-virtual members that aren't destructors or trivial constructors don't stop it being considered POD), and the newer (and more directly comparable) POCO "Plain Old CLR Object" in .NET.
According to Martin Fowler
The term was coined while Rebecca Parsons, Josh MacKenzie and I were preparing for a talk at a conference in September 2000. In the talk, we were pointing out the many benefits of encoding business logic into regular java objects rather than using Entity Beans. We wondered why people were so against using regular objects in their systems and concluded that it was because simple objects lacked a fancy name. So we gave them one, and it’s caught on very nicely.
Generally, a POJO is not bound to any restriction and any Java object can be called a POJO but there are some directions. A well-defined POJO should follow below directions.
Each variable in a POJO should be declared as private.
Default constructor should be overridden with public accessibility.
Each variable should have its Setter-Getter method with public accessibility.
Generally POJO should override equals(), hashCode() and toString() methods of Object (but it's not mandatory).
Overriding compare() method of Comparable interface used for sorting (Preferable but not mandatory).
And according to Java Language Specification, a POJO should not have to
Extend pre-specified classes
Implement pre-specified interfaces
Contain pre-specified annotations
However, developers and frameworks describe a POJO still requires the use prespecified annotations to implement features like persistence, declarative transaction management etc. So the idea is that if the object was a POJO before any annotations were added would return to POJO status if the annotations are removed then it can still be considered a POJO.
A JavaBean is a special kind of POJO that is Serializable, has a no-argument constructor, and allows access to properties using getter and setter methods that follow a simple naming convention.
Read more on Plain Old Java Object (POJO) Explained.
there are mainly three options are possible for mapping purpose
serialize
XML mapping
POJO mapping.(Plain Old Java Objects)
While using the pojo classes,it is easy for a developer to map with the database.
POJO classes are created for database and at the same time value-objects classes are created with getter and setter methods that will easily hold the content.
So,for the purpose of mapping in between java with database, value-objects and POJO classes are implemented.
import java.io.Serializable;
public class Course implements Serializable {
protected int courseId;
protected String courseName;
protected String courseType;
public Course() {
courseName = new String();
courseType = new String();
}
public Course(String courseName, String courseType) {
this.courseName = courseName;
this.courseType = courseType;
}
public Course(int courseId, String courseName, String courseType) {
this.courseId = courseId;
this.courseName = courseName;
this.courseType = courseType;
}
public int getCourseId() {
return courseId;
}
public void setCourseId(int courseId) {
this.courseId = courseId;
}
public String getCourseName() {
return courseName;
}
public void setCourseName(String courseName) {
this.courseName = courseName;
}
public String getCourseType() {
return courseType;
}
public void setCourseType(String courseType) {
this.courseType = courseType;
}
#Override
public int hashCode() {
return courseId;
}
#Override
public boolean equals(Object obj) {
if (obj != null || obj instanceof Course) {
Course c = (Course) obj;
if (courseId == c.courseId && courseName.equals(c.courseName)
&& courseType.equals(c.courseType))
return true;
}
return false;
}
#Override
public String toString() {
return "Course[" + courseId + "," + courseName + "," + courseType + "]";
}
}
public class UserInfo {
String LoginId;
String Password;
String FirstName;
String LastName;
String Email;
String Mobile;
String Address;
String DOB;
public String getLoginId() {
return LoginId;
}
public void setLoginId(String loginId) {
LoginId = loginId;
}
public String getPassword() {
return Password;
}
public void setPassword(String password) {
Password = password;
}
public String getFirstName() {
return FirstName;
}
public void setFirstName(String firstName) {
FirstName = firstName;
}
public String getLastName() {
return LastName;
}
public void setLastName(String lastName) {
LastName = lastName;
}
public String getEmail() {
return Email;
}
public void setEmail(String email) {
Email = email;
}
public String getMobile() {
return Mobile;
}
public void setMobile(String mobile) {
Mobile = mobile;
}
public String getAddress() {
return Address;
}
public void setAddress(String address) {
Address = address;
}
public String getDOB() {
return DOB;
}
public void setDOB(String DOB) {
this.DOB = DOB;
}
}
File-setting-plugins-Browse repositories
Search RoboPOJOGenerator and install, Restart Android studio
Open Project and right click on package select on Generate POJO from JSON
Paste JSON in dialogbox and select option according your requirements
Click on Generate button
If a class is not bogged down from a framework or a library, then an object created from that class is recognized as a POJO.
Let's see some examples:
class MyServlet extends HttpServlet{
//....
}
The sole meaning of MyServlet class is given by the HttpServlet class. Therefore the objects created from the MyServlet are not POJOs.
class MyClass implements Serializable{
//...
}
The Serializable interface does not give a meaning to the class MyClass. Therefore the objects created from the MyClass are POJOs.