JSF 2 生命周期
我有 BookModel.java 的代码：
@Entity
@Table(name = "BOOK")
@NamedNativeQuery(name = "BookModel.findBookTitle", query = "SELECT @rownum:=@rownum+1 'no', m.title, m.author, REPLACE(SUBSTRING_INDEX(m.content, ' ', 30), '<br>', ' '), m.viewed, m.hashid FROM book m, (SELECT @rownum:=0) r WHERE m.title like 'a%'")
public class BookModel implements Serializable
{
@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "MY_SEQ_GEN")
@Column(name = "id", unique = true, nullable = false)
private Long id;
@NotNull
@Size(min = 1, max = 255)
@Column(name = "title")
private String title;
@NotNull
@Size(min = 1, max = 255)
@Column(name = "author")
private String author;
}
业务层的 BookService.java：
@Stateless
public class BookService
{
@SuppressWarnings("unchecked")
public List<BookModel> getBook() {
Query query = entityManager.createNamedQuery("BookModel.findBookTitle");
List<BookModel> result = query.getResultList();
return result;
}
}
表示层的 BookBean.java：
@ManagedBean(name = "BookBean")
@RequestScoped
public class BookBean implements Serializable
{
@EJB
private BookService bookService;
private DataModel<BookModel> book;
public DataModel<BookModel> getBook() {
return book;
}
}
页面 book.xhtml：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:ui="http://java.sun.com/jsf/facelets"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:f="http://java.sun.com/jsf/core"
xmlns:p="http://primefaces.prime.com.tr/ui">
<p:dataTable id="bookList" value="#{BookBean.book}" var="book">
...
</p:dataTable>
</html>
我的问题是： 如何限制方法 getBook() 在 BookBean 中只执行一次而不是六次 - 大概是针对 JSF 生命周期的每个阶段。以前有其他人遇到过这个吗？请帮忙。最后一天一直坚持这个，没有成功。
I have this code for BookModel.java:
@Entity
@Table(name = "BOOK")
@NamedNativeQuery(name = "BookModel.findBookTitle", query = "SELECT @rownum:=@rownum+1 'no', m.title, m.author, REPLACE(SUBSTRING_INDEX(m.content, ' ', 30), '<br>', ' '), m.viewed, m.hashid FROM book m, (SELECT @rownum:=0) r WHERE m.title like 'a%'")
public class BookModel implements Serializable
{
@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "MY_SEQ_GEN")
@Column(name = "id", unique = true, nullable = false)
private Long id;
@NotNull
@Size(min = 1, max = 255)
@Column(name = "title")
private String title;
@NotNull
@Size(min = 1, max = 255)
@Column(name = "author")
private String author;
}
And BookService.java for the business layer:
@Stateless
public class BookService
{
@SuppressWarnings("unchecked")
public List<BookModel> getBook() {
Query query = entityManager.createNamedQuery("BookModel.findBookTitle");
List<BookModel> result = query.getResultList();
return result;
}
}
And BookBean.java for the presentation layer:
@ManagedBean(name = "BookBean")
@RequestScoped
public class BookBean implements Serializable
{
@EJB
private BookService bookService;
private DataModel<BookModel> book;
public DataModel<BookModel> getBook() {
return book;
}
}
And the page book.xhtml:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:ui="http://java.sun.com/jsf/facelets"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:f="http://java.sun.com/jsf/core"
xmlns:p="http://primefaces.prime.com.tr/ui">
<p:dataTable id="bookList" value="#{BookBean.book}" var="book">
...
</p:dataTable>
</html>
My question is: How can I restrict the method getBook() in BookBean to be executed only once instead of six times - presumably for each phase of JSF lifecycle. Has anyone else come across this before? Please help. Have been stuck on this for the last day without any success.
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那是不可能的。它通常不会造成伤害。 Getter 的作用只是提供对 Bean 属性的访问点，而不是执行某些业务工作。
如果您确实在该托管 bean 方法中调用了 @EJB 的 getBook() 方法（如下所示）
，那么这确实会很昂贵，因为它会多次调用数据库作为吸气剂的名称。您希望在 bean 的构造函数或
@PostConstruct中完成这项工作。另请参阅：
与以下内容无关具体问题是，方法名称
getBook()和变量名称book并不是真正的自文档化，因为它实际上包含不止一本书。我会使用getBooks()和books来代替。That's not possible. It should usually not harm. Getters are solely there to provide access points to bean properties, not to do some business jobs.
If you did call the
@EJBsgetBook()method inside that managed bean method like followsthen this is indeed going to be expensive as it would call the DB that much times as the getter is called. You would like to do the job in the bean's constructor or
@PostConstructinstead.See also:
Unrelated to the concrete problem, the method name
getBook()and variable namebookis not really self-documenting since it actually contains more than one book. I'd usegetBooks()andbooksinstead.