I've decided to use Value Objects instead of String fields in my entity and I don't know how (and if it's even possible) to validate them using JPA Annotations like #Size, #Pattern and so on.
Here is my Book entity:
#Entity
#Access(AccessType.FIELD) // so I can avoid using setters for fields that won't change
public class Book {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long bookId;
#Embedded
private Isbn isbn;
#Embedded
private Title title;
#Embedded
private Author author;
#Embedded
private Genre genre;
#Embedded
private PublicationYear publicationYear;
private BigDecimal price;
// jpa requirement
public Book() {
}
public Book(Isbn isbn, Title title, Author author, Genre genre, PublicationYear publicationYear,
BigDecimal price) {
this.isbn = isbn;
this.title = title;
this.author = author;
this.genre = genre;
this.publicationYear = publicationYear;
this.price = price;
}
public Long getBookId() {
return bookId;
}
public Isbn getIsbn() {
return isbn;
}
public Title getTitle() {
return title;
}
public Author getAuthor() {
return author;
}
public Genre getGenre() {
return genre;
}
public BigDecimal getPrice() {
return price;
}
public PublicationYear getPublicationYear() {
return publicationYear;
}
// setter for price is needed because price of the book can change (discounts and so on)
public void setPrice(BigDecimal price) {
this.price = price;
}
}
And here is my example value object - all are just using Strings.
public class Isbn {
private String isbn;
// jpa requirement
public Isbn() {
}
public Isbn(String isbn) {
this.isbn = isbn;
}
public String getIsbn() {
return isbn;
}
#Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
Isbn isbn1 = (Isbn) o;
return isbn != null ? isbn.equals(isbn1.isbn) : isbn1.isbn == null;
}
#Override
public int hashCode() {
return isbn != null ? isbn.hashCode() : 0;
}
#Override
public String toString() {
return "Isbn{" +
"isbn='" + isbn + '\'' +
'}';
}
}
Is there a simple way to validate those objects? If it was a String in my entity instead of Isbn object I could just use #Pattern to match correct Isbn and be done with it.
EDIT1: Maybe there is a better way to validate value objects than above one? I'm kinda new to this stuff so would like to know if there is a better option to validate my entities.
You can enforce validation of Object fields by utilizing #Valid annotation;
#Entity
#Access(AccessType.FIELD)
public class Book {
#Embedded #Valid
private Isbn isbn;
...
}
public class Isbn {
#Pattern(//Pattern you'd like to enforce)
private String isbn;
...
}
Then you can validate by yourself using the following;
ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
Validator validator = factory.getValidator();
Set<ConstraintViolation<User>> violations = validator.validate(book);
//if set is empty, validation is OK
Related
I am trying to create two entities which have many-to-many relation between them. First entity is Person with PID as primary key, second is Serie with SID as primary key. In database there is a table TJV_5_SERIE_2_PERSON, which represents many to many relationship between these entities.
tables in database
The problem is when I retrieve any entity, Collection annotated with #ManyToMany is always empty. So I assume I've messed up something in my code that explains why my many-to-many relation doesn't work.
I retrieve these two entities by generating (in Netbeans 9.0) 'Restful Web Services from Entity classes'. This way I can use these services to retrieve all attributes succesfully, except Collection with #ManyToMany annotation is always empty.
Any idea why it is not woking appreciated. It is first time trying this, so pardon me for any dumm mistakes.
Person class:
#Entity
#Table(name = "TJV_5_PERSON")
#XmlRootElement
public class Person implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "PID")
private Integer id;
#Column(name = "PNAME")
private String name;
#ManyToMany()
#JoinTable(
name = "TJV_5_SERIE_2_PERSON",
joinColumns = #JoinColumn(name = "PID", referencedColumnName = "PID"),
inverseJoinColumns = #JoinColumn(name = "SID", referencedColumnName = "SID")
)
// always empty
private Collection<Serie> favourites = new ArrayList<Serie>();
public Person() {
}
public Person(Integer id, String name) {
this.id = id;
this.name = name;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
#XmlTransient
public Collection<Serie> getFavourites() {
return favourites;
}
public void setFavourites(Collection<Serie> favourites) {
this.favourites = favourites;
}
#Override
public int hashCode() {
int hash = 5;
hash = 31 * hash + Objects.hashCode(this.id);
return hash;
}
#Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj == null) {
return false;
}
if (getClass() != obj.getClass()) {
return false;
}
final Person other = (Person) obj;
if (!Objects.equals(this.id, other.id)) {
return false;
}
return true;
}
#Override
public String toString() {
return "Person{" + "id=" + id + ", name=" + name + ", favourites=" + favourites + '}';
}
}
Serie class:
#Entity
#Table(name = "TJV_5_SERIE")
#XmlRootElement
public class Serie implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "SID")
private Integer id;
#Column(name = "STITLE")
private String title;
// always empty
#ManyToMany(mappedBy = "favourites")
private Collection<Person> fans = new ArrayList<Person>();
public Serie() {
}
public Serie(Integer id, String title) {
this.id = id;
this.title = title;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
#XmlTransient
public Collection<Person> getFans() {
return fans;
}
public void setFans(Collection<Person> fans) {
this.fans = fans;
}
#Override
public int hashCode() {
int hash = 3;
hash = 67 * hash + Objects.hashCode(this.id);
return hash;
}
#Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj == null) {
return false;
}
if (getClass() != obj.getClass()) {
return false;
}
final Serie other = (Serie) obj;
if (!Objects.equals(this.id, other.id)) {
return false;
}
return true;
}
#Override
public String toString() {
return "Serie{" + "id=" + id + ", title=" + title + ", fans=" + fans + '}';
}
}
I am not 100% sure, but you may not retrieving any results beacuse of #XMLTransiet annotation above the Serie.class method
#XmlTransient
public Collection<Person> getFans() {
return fans;
}
Try to look in documentation https://docs.oracle.com/javaee/6/api/javax/xml/bind/annotation/XmlTransient.html or in connected posts Hide an entity variable from xml message - #XmlTransient not working
The other issue is cascading data between two corresponding #ManyToMany tables. It means that you have intersection and the data appears in this table automatically when you use some type of cascade but you need send a POST request. It means in your service class layer you can create a method responsible for creating Person and assign a Serie to this Person object which is a foreign key. The article about cascading is here :) https://vladmihalcea.com/a-beginners-guide-to-jpa-and-hibernate-cascade-types/
Given an Enitiy Product
#Entity
public class Product {
private Long id;
private List<Review> reviews;
public Product() {}
#Id
#GeneratedValue
public Long getId() {
return this.id;
}
public void setId(Long id) {
this.id = id;
}
#ElementCollection
public List<Review> getReviews() {
return reviews;
}
public void setReviews(List<Review> reviews) {
this.reviews = reviews;
}
// equals() and hashCode() omitted for brevity
}
And an Embeddable Review
#Embeddable
public class Review {
private Customer author;
private String title;
private String comment;
public Review() {}
#ManyToOne(optional = false)
#Column(unique = true)
public Customer getAuthor() {
return author;
}
public void setAuthor(Customer author) {
this.author = author;
}
#Column(nullable = false)
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
#Column(nullable = false, length = 2000)
public String getComment() {
return comment;
}
public void setComment(String comment) {
this.comment = comment;
}
}
How can I set an unique constraint for the Review's author. In other words: I want to make sure, that for a given product each review has a different author.
Can I use #NaturalId? Do I use #Column(unique = true)? I already found a similar question on StackOverflow, but in my case it's a list of Embeddables and not just a member, so that that approach won't work, I guess.
Thanks a lot in advance!
If you are talking about having a unique database index added during schema generation then you can do this as below:
#ElementCollection
#CollectionTable(name = "product_reviews",
uniqueConstraints = {#UniqueConstraint(columnNames={"product_id", "author_id"})})
public List<Review> getReviews() {
return reviews;
}
I'm trying to insert objects of type Book into a database, and one of the columns is specified as date, but according to this exception:
Caused by: org.postgresql.util.PSQLException: ERROR: column "publish_date" is of type date but expression is of type bytea
Hint: You will need to rewrite or cast the expression.
Position: 94
at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2412)
at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:2125)
at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:297)
at org.postgresql.jdbc.PgStatement.executeInternal(PgStatement.java:428)
at org.postgresql.jdbc.PgStatement.execute(PgStatement.java:354)
at org.postgresql.jdbc.PgPreparedStatement.executeWithFlags(PgPreparedStatement.java:169)
at org.postgresql.jdbc.PgPreparedStatement.executeUpdate(PgPreparedStatement.java:136)
at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:204)
... 11 more
is being put in as bytea. I'm not sure why this is the case, because in the database the column itself is of type date, and the column in my Book class is of type date. I can show the code below:
package examples.pubhub.model;
import java.time.LocalDate;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;
#Entity
#Table(name="books")
public class Book {
#Id
#Column(name="isbn_13")
public String isbn_13; // International Standard Book Number, unique
#Column(name="title")
private String title;
#Column(name="author")
private String author;
#Column(name="publish_date")
private LocalDate publish_date; // Date of publish to the website
#Column(name="price")
private double price;
#Column(name="content")
private byte[] content;
// Constructor used when no date is specified
public Book(String isbn, String title, String author, byte[] content, double price) {
super();
this.isbn_13 = isbn;
this.title = title;
this.author = author;
this.publish_date = LocalDate.now();
this.content = content;
this.price = price;
}
// Constructor used when a date is specified
public Book(String isbn, String title, String author, LocalDate publishDate, double price, byte[] content) {
super();
this.isbn_13 = isbn;
this.title = title;
this.author = author;
this.publish_date = publishDate;
this.content = content;
this.price = price;
}
// Default constructor
public Book() {
}
public String getIsbn_13() {
return isbn_13;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
public LocalDate getPublish_date() {
return publish_date;
}
public void setPublish_date(LocalDate publishDate) {
this.publish_date = publishDate;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
public byte[] getContent() {
return content;
}
public void setContent(byte[] content) {
this.content = content;
}
public void setIsbn_13(String isbn) {
this.isbn_13 = isbn;
}
}
And this is the offline class I'm testing:
package examples.pubhub.utilities;
import java.time.LocalDate;
import examples.pubhub.dao.BookDAO;
import examples.pubhub.dao.BooktagDAO;
import examples.pubhub.model.Book;
import examples.pubhub.model.Booktag;
public class PublishBookTest {
public static void main(String[] args) {
// TODO Auto-generated method stub
String isbn = "1234123412341";
String title = "Title";
String author = "Haisam";
String book_tag = "Science Fiction";
BookDAO database = DAOUtilities.getBookDAO();
Book tempBook = database.getBookByISBN(isbn);
BooktagDAO tagdao = DAOUtilities.getBooktagDAO();
Booktag tempBooktag = tagdao.getBookTagByISBN(isbn);
if (tempBook != null && tempBooktag != null) {
// ASSERT: book with isbn already exists
System.out.println("ISBN already exists.");
} else {
Book book = new Book();
Booktag booktag = new Booktag();
book.setIsbn_13(isbn);
book.setTitle(title);
book.setAuthor(author);
book.setPrice(124);
book.setPublish_date(LocalDate.now());
book.setContent(null);
booktag.setBook_tag(book_tag);
booktag.setBook_isbn(isbn);
booktag.setBook_title(title);
boolean isSuccess_booktag = tagdao.addTag(booktag);
boolean isSuccess_book = database.addBook(book);
if (isSuccess_book && isSuccess_booktag) {
System.out.println("Added.");
} else {
System.out.println("Not added.");
}
}
}
}
If anyone knows how to convert from bytea to date, or what the crux of this problem may be, I will be forever grateful. Thank you for your time.
TLDR: The transaction is not committing because of incompatible typing between LocalDate publish_date and the actual column publish_date in the database, which is of type date. Not sure why.
Create a LocalDateToWhateverDBTypeConverter. Here is how.
Edit:
There are two options to define the usage of a Converter. The first one is to set autoapply=true at the #Converter annotation of the Converter class. In this case the JPA provider will use this Converter to convert all entity attributes of the given type.
If autoapply is set to false, you need to add the javax.persistence.Convert annotation to all attributes that shall be converted and specify the Converter class. The following code snippet shows an example for this approach:
#Entity
public class RectangleEntity
{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
#Column
private Integer x;
#Column
private Integer y;
#Column
#Convert(converter = ColorConverter.class)
private Color color;
...
}
I'm trying to read an XML document and decode it in to Java Beans. I have the reading part settled but I run in to an issue. I'm basically trying to decode all the child nodes of the XML document, root being "catalog". How do I do this using the XMLDecoder?
XMLDecoder:
private static Book jaxbXMLToObject() {
try {
JAXBContext context = JAXBContext.newInstance(Book.class);
Unmarshaller un = context.createUnmarshaller();
Book book = (Book) un.unmarshal(new File("PATH"));
return book;
} catch (JAXBException e) {
e.printStackTrace();
}
return null;
}
I'm trying to read the following document
<?xml version="1.0"?>
<catalog>
<book id="1">
<author>Isaac Asimov</author>
<title>Foundation</title>
<genre>Science Ficition</genre>
<price>164</price>
<publish_date>1951-08-21</publish_date>
<description>Foundation is the first novel in Isaac Asimovs Foundation Trilogy (later expanded into The Foundation Series). Foundation is a cycle of five interrelated short stories, first published as a single book by Gnome Press in 1951. Collectively they tell the story of the Foundation, an institute to preserve the best of galactic civilization after the collapse of the Galactic Empire.</description>
</book>
</catalog>
And Parse it in to a Book Object
#XmlRootElement(name = "book")
#XmlType(propOrder = {"id", "price", "title", "author", "genre", "description"})
public class Book {
private int id;
private int price;
private String title;
private String author;
private String genre;
private String description;
private Date publish_date;
public Book() {
}
......
I get the error: jjavax.xml.bind.UnmarshalException: unexpected element (uri:"", local:"catalog"). Expected elements are <{}book>
How do I only access the child nodes using JAXB?
UPDATE
Catalog Class:
#XmlRootElement(name = "catalog")
public class Catalog {
#XmlElement(name = "book")
List<Book> books;
public List<Book> getBooks() {
return books;
}
public void setBooks(List<Book> books) {
this.books = books;
}
}
Book class:
#XmlAccessorType(XmlAccessType.FIELD)
public class Book {
#XmlAttribute
int id;
private int price;
private String title;
private String author;
private String genre;
private String description;
private Date publish_date;
public Book() {
}
public Book(int id, int price, String title, String genre, String description, Date publicationDate) {
this.id = id;
this.price = price;
this.title = title;
this.genre = genre;
this.description = description;
this.publish_date = publicationDate;
}
public int getId() {
return id;
}
public int getPrice() {
return price;
}
public String getTitle() {
return title;
}
public String getGenre() {
return genre;
}
public String getDescription() {
return description;
}
public Date getPublicationDate() {
return publish_date;
}
public void setId(int id) {
this.id = id;
}
public void setPrice(int price) {
this.price = price;
}
public void setTitle(String title) {
this.title = title;
}
public void setGenre(String genre) {
this.genre = genre;
}
public void setDescription(String description) {
this.description = description;
}
public void setPublish_date(String publish_date) {
this.publish_date = new Date();
}
public String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
public Date getPublish_date() {
return publish_date;
}
public String toJSON() {
ObjectMapper mapper = new ObjectMapper();
try {
return mapper.writeValueAsString(this);
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
#Override
public String toString() {
return "Book{" +
"id=" + id +
", price=" + price +
", title='" + title + '\'' +
", genre='" + genre + '\'' +
", description='" + description + '\'' +
", publicationDate=" + publish_date +
'}';
}
}
DAO:
public class BooksDAO {
public BooksDAO() {
}
public List<Book> getBooks() {
Catalog catalog = jaxbXMLToObject();
return catalog.getBooks();
}
private static Catalog jaxbXMLToObject() {
try {
return JAXB.unmarshal(new File("PATH"), Catalog.class);
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
}
As already pointed out by JB Nizet you definitely need an enclosing Catalog object. The following is the bare minimum to be able to unmarshal the provided XML document using JAXB and extract the book from it:
public class ReadXMLUsingJAXB {
static class Catalog {
#XmlElement(name = "book")
List<Book> books;
}
#XmlAccessorType(XmlAccessType.FIELD)
static class Book {
#XmlAttribute
int id;
String author;
String title;
String genre;
int price;
Date publish_date;
String description;
}
private static Book firstBookFromXML() {
Catalog catalog = JAXB.unmarshal(new File("PATH"), Catalog.class);
return catalog.books.get(0);
}
public static void main(String[] args) {
Book book = firstBookFromXML();
System.out.println(book.id + ", " + book.author + ", " + book.title
+ ", " + book.genre + ", " + book.price
+ ", " + book.publish_date + ", " + book.description);
}
}
Some things are worth mentioning here:
The #XmlAccessorType-Annotation is not necessary with Catalog as there is only one field which is annotated with #XmlElement.
When chosing FIELD as access type all fields are taken into account regardless of their visibility unless annotated with #XmlTransient.
The book ID is an attribute in the document, so it must be declared as such using #XmlAttribute.
#XmlElement on Catalog.books was necessary to reflect the name of the book-Elements. JAXB defaults to the field (or property) name which would be books instead and thus not match the elements.
As said before the demonstration code is the bare minimum and should be changed to fit your needs (i.e. field visibility, proper constructor, getters, equals, hashCode, toString etc.)
I am learning Java as of right now and have just been learned what constructors are. I do not understand why you would need more than one constructor if you need to initialize all variables.
To put it simply, you use multiple constructors for convenience (1st example) or to allow completely different initialization methods or different source types (2nd example.
You might need multiple constructors to implement your class to simply allow omitting some of the parameters that are already setup:
//The functionality of the class is not important, just keep in mind parameters influence it.
class AirConditioner{
enum ConditionerMode{
Automatic, //Default
On,
Off
}
public ConditionerMode Mode; //will be on automatic by default.
public int MinTemperature = 18;
public int MaxTemperature = 20;
public AirConditioner(){ //Default constructor to use default settings or initialize manually.
//Nothing here or set Mode to Automatic.
}
//Mode
public AirConditioner(ConditionerMode mode){ //Setup mode, but leave the rest at default
Mode = mode;
}
//setup everything.
public AirConditioner(ConditionerMode mode, int MinTemp, int MaxTemp){
Mode = mode;
MinTemperature = MinTemp;
MaxTemperature = MaxTemp;
}
}
Another example is when different constructors follow different procedures to initialize the variables.
For instance you could have a data table that simply displays a table of text. The constructor could get the data from either database OR a file:
class DataTable{
public DataTable(){} //Again default one, in case you want to initialize manually
public DataTable(SQLConnection con, SQLCommand command){
//Code to connect to database get the data and fill the table
}
public DataTable(File file){
//Code to read data from a file and fill the table
}
}
A class can have multiple constructors, as long as their signature (the parameters they take) are not the same. You can define as many constructors as you need. When a Java class contains multiple constructors, we say that the constructor is overloaded (comes in multiple versions). This is what constructor overloading means, that a Java class contains multiple constructors.
Having said that, it is completely dependent upon your implementation whether or not you want to create more than one constructor in your class but having more than one constructor can ease your life in many instances. Suppose below class doesn't have a default constructor:
public class Employee {
private int age;
private String name;
Employee(int age, String name){
this.age=age;
this.name=name;
}
}
So, while creating object of this class user would not be able to do so until he has age and name parameters handy which restricts the true functionality of Java objects as Objects' state should be able to be modified and populated at any time once initialized.
Per constructor has specific purpose. Sometimes we need more than one constructor (special in Entity domain case, when use ORM)
For example:
Empty constructor (no arguments) for reflection,
Constructor has argument(s) for create new instance (A a = new A('foo', 'bar');).
These're overload method(s).
Reality example:
package sagan.blog;
import com.fasterxml.jackson.annotation.JsonIgnore;
import org.hibernate.annotations.Type;
import org.springframework.util.StringUtils;
import sagan.team.MemberProfile;
import javax.persistence.*;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.HashSet;
import java.util.Set;
/**
* JPA Entity representing an individual blog post.
*/
#Entity
#SuppressWarnings("serial")
public class Post {
private static final SimpleDateFormat SLUG_DATE_FORMAT = new SimpleDateFormat("yyyy/MM/dd");
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#ManyToOne(cascade = CascadeType.PERSIST, optional = false)
private MemberProfile author;
#Column(nullable = false)
private String title;
#Column(nullable = false)
#Enumerated(EnumType.STRING)
private PostCategory category;
#Column(nullable = false)
#Enumerated(EnumType.STRING)
private PostFormat format;
#Column(nullable = false)
#Type(type = "text")
private String rawContent;
#Column(nullable = false)
#Type(type = "text")
private String renderedContent;
#Column(nullable = false)
#Type(type = "text")
private String renderedSummary;
#Column(nullable = false)
private Date createdAt = new Date();
#Column(nullable = false)
private boolean draft = true;
#Column(nullable = false)
private boolean broadcast = false;
#Column(nullable = true)
private Date publishAt;
#Column(nullable = true)
private String publicSlug;
#ElementCollection
private Set<String> publicSlugAliases = new HashSet<>();
#SuppressWarnings("unused")
private Post() {
}
public Post(String title, String content, PostCategory category, PostFormat format) {
this.title = title;
this.rawContent = content;
this.category = category;
this.format = format;
}
/* For testing only */
public Post(Long id, String title, String content, PostCategory category, PostFormat format) {
this(title, content, category, format);
this.id = id;
}
public Long getId() {
return id;
}
public MemberProfile getAuthor() {
return author;
}
public void setAuthor(MemberProfile author) {
this.author = author;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public PostCategory getCategory() {
return category;
}
public void setCategory(PostCategory category) {
this.category = category;
}
public PostFormat getFormat() {
return format;
}
public void setFormat(PostFormat format) {
this.format = format;
}
public String getRawContent() {
return rawContent;
}
public void setRawContent(String rawContent) {
this.rawContent = rawContent;
}
public String getRenderedContent() {
return renderedContent;
}
public void setRenderedContent(String renderedContent) {
this.renderedContent = renderedContent;
}
public String getRenderedSummary() {
return renderedSummary;
}
public void setRenderedSummary(String renderedSummary) {
this.renderedSummary = renderedSummary;
}
public Date getCreatedAt() {
return createdAt;
}
public void setCreatedAt(Date createdAt) {
this.createdAt = createdAt;
}
public Date getPublishAt() {
return publishAt;
}
public void setPublishAt(Date publishAt) {
this.publishAt = publishAt;
publicSlug = publishAt == null ? null : generatePublicSlug();
}
public boolean isDraft() {
return draft;
}
public void setDraft(boolean draft) {
this.draft = draft;
}
public void setBroadcast(boolean isBroadcast) {
broadcast = isBroadcast;
}
public boolean isBroadcast() {
return broadcast;
}
#JsonIgnore
public boolean isScheduled() {
return publishAt == null;
}
#JsonIgnore
public boolean isLiveOn(Date date) {
return !(isDraft() || publishAt.after(date));
}
public String getPublicSlug() {
return publicSlug;
}
public void addPublicSlugAlias(String alias) {
if (alias != null) {
this.publicSlugAliases.add(alias);
}
}
#JsonIgnore
public String getAdminSlug() {
return String.format("%s-%s", getId(), getSlug());
}
private String generatePublicSlug() {
return String.format("%s/%s", SLUG_DATE_FORMAT.format(getPublishAt()), getSlug());
}
#JsonIgnore
private String getSlug() {
if (title == null) {
return "";
}
String cleanedTitle = title.toLowerCase().replace("\n", " ").replaceAll("[^a-z\\d\\s]", " ");
return StringUtils.arrayToDelimitedString(StringUtils.tokenizeToStringArray(cleanedTitle, " "), "-");
}
#Override
public String toString() {
return "Post{" + "id=" + id + ", title='" + title + '\'' + '}';
}
}
Class Post even has 3 constructors named Post(){...}
Source: https://github.com/spring-io/sagan/blob/master/sagan-common/src/main/java/sagan/blog/Post.java
So, recall that the purpose of the constructor is to initialize (give them values).
So think of this model:
public class Car{
private String model; //Objects are null
private int year; // year = 0
Car(String model, int year ){
this.model = model;
this.year = year;
}
}
The Car object you create needs values for the model and the year. It would be great if you could just create a dummy car with just default values for each field, or take a string that looks like this:
"Ford 2016 or "Ford" and "2016" and create a Car object.
So, just create two more constructors with different signatures that accomplish that task.
Also, imagine we have another String field called owner. The owner of a car may not be know at the creation of this object, but your program may be able to function without it. So, we can use the same constructor above and the Car object's owner field will be set to null.
That's the purpose for multiple constructors. To give the programmer flexibility on saying what an object can be created from and which variables need to be initialized in the first place.
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