问题描述
我在此应用程序中使用了Hibernate。我正在尝试从数据库调用数据到jTable。当数据库为空时,正在编译代码,但是当我向MysqL表程序中添加数据时,抛出java.util.ConcurrentModificationException。
public FrmMain() {
initialize();
getData();
}
public void getData() {
model = (DefaultTableModel) tblBookList.getModel();
List<Book> books = new ArrayList<>(bookManager.getBook());
ListIterator<Book> listIterator = books.listIterator();
while(listIterator.hasNext()) {
Book book = listIterator.next();
Object[] row = { book.getName(),book.getAuthor(),book.getPublisher(),book.getPage(),book.getTranslator(),book.getPublishYear(),book.getType()
};
model.addRow(row);
}
}
public class MysqLBookDal implements IBookDal {
SessionFactory factory = new Configuration()
.configure("MysqLHibernate.cfg.xml")
.addAnnotatedClass(Book.class)
.buildSessionFactory();
Session session = factory.getCurrentSession();
public List<Book> select() {
List<Book> books = new copyOnWriteArrayList<Book>();
try {
session.beginTransaction();
books = session.createquery("from Book").getResultList();
for(Book book: books) {
books.add(book);
}
session.getTransaction().commit();
} finally {
factory.close();
}
return books;
}
有人可以帮助我吗? 堆栈跟踪:
ERROR: Connection leak detected: there are 1 unclosed connections upon
shutting down pool jdbc:MysqL://localhost:3306/book?useUnicode=true&useLegacyDatetimeCode=false&serverTimezone=Turkey
java.util.ConcurrentModificationException
at java.base/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:1013)
at java.base/java.util.ArrayList$Itr.next(ArrayList.java:967)
at com.github.bookManagementSystem.dataAccess.MysqLBookDal.select(MysqLBookDal.java:32)
at com.github.bookManagementSystem.business.BookManager.getBook(BookManager.java:20)
at com.github.bookManagementSystem.FrmMain.getData(FrmMain.java:98)
at com.github.bookManagementSystem.FrmMain.<init>(FrmMain.java:90)
at com.github.bookManagementSystem.FrmMain$1.run(FrmMain.java:76)
at java.desktop/java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:316)
at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:770)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:740)
at java.desktop/java.awt.EventdispatchThread.pumpOneEventForFilters(EventdispatchThread.java:203)
at java.desktop/java.awt.EventdispatchThread.pumpEventsForFilter(EventdispatchThread.java:124)
at java.desktop/java.awt.EventdispatchThread.pumpEventsForHierarchy(EventdispatchThread.java:113)
at java.desktop/java.awt.EventdispatchThread.pumpEvents(EventdispatchThread.java:109)
at java.desktop/java.awt.EventdispatchThread.pumpEvents(EventdispatchThread.java:101)
at java.desktop/java.awt.EventdispatchThread.run(EventdispatchThread.java:90)
解决方法
尝试使用CopyOnWriteArrayList
代替ArrayList
。这将允许并发修改。但是请注意,如果您要更改列表很多,这不是很有效。但是,如果您大部分时间在读书,那应该没问题。
ConcurrentModificationException
被抛出,因为您正在将元素添加到要迭代的同一列表中。在这里:
for(Book book : books) {
books.add(book);
}
此代码是错误的。
您可以返回Hibernate返回的List
实例,也可以创建一个新列表。
您不需要使用CopyOnWriteArrayList
!这是非常昂贵的数据结构。您的错误与同时修改和访问列表的不同线程无关。此外,您不需要针对数据库启动显式事务,因为您只是在阅读。整个select
方法可以完全简化为:
public List<Book> select() {
return new ArrayList<>(session.createQuery("from Book").getResultList());
}
您也不需要关闭factory
。
@DuncG可以解决您的紧迫问题。
假设您通过start.spring.io下载所需的依赖项,则使用Spring Boot可以将您的代码简化为以下代码:
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
@Repository
public interface BookRepository extends JpaRepository<Book,Long> {
}
在您的服务课程中:
@Autowired //or use constructor injection
BookRepository BookRepository;
public List<Book> findAll() {
return bookRepository.findAll();
}
JpaRepository
继承了findAll()
方法以及带有CRUD存储库的其他非常常见的行为。有关更多详细信息,请参见docs。