Anandloni

Wednesday, July 7, 2010

Deleting childeren in Hibernate

Lets take example of One to many relationship between Author and Book.

If you want to delete book without deleting parent i.e author you could simply delete using

delete(book)

which will cause :

org.springframework.dao.InvalidDataAccessApiUsageException: deleted object would be re-saved by cascade (remove deleted object from associations): [Book#1]; ...

at org.springframework.orm.hibernate3.SessionFactoryUtils.convertHibernateAccessException(SessionFactoryUtils.java:657)

at org.springframework.orm.hibernate3.HibernateAccessor.convertHibernateAccessException(HibernateAccessor.java:412)

at org.springframework.orm.hibernate3.HibernateTemplate.doExecute(HibernateTemplate.java:411)

at org.springframework.orm.hibernate3.HibernateTemplate.executeWithNativeSession(HibernateTemplate.java:374)

at org.springframework.orm.hibernate3.HibernateTemplate.flush(HibernateTemplate.java:881)

at ConsoleScript7.run(ConsoleScript7:3)

Caused by: org.hibernate.ObjectDeletedException: deleted object would be re-saved by cascade (remove deleted object from associations): [Book#1] 

The problem is that the books are still in the author's collection, so when the session is flushed, they will be recreated. Solution will be remove the book from the collection itself.

author.getBooks().remove(bookId) 

and then save author object.

Friday, June 25, 2010

Reading file from URL into byte array output stream

Here is code which reads file from URL and writes to ByteArrayOutPutStream

try

{

InputStream is = new URL("http://localhost:8080/pdf/test.pdf").openStream();

ByteArrayOutputStream outputDoc = new ByteArrayOutputStream();

byte buf[]=new byte[1024];

int len;

while((len=is.read(buf))>0)

{

outputDoc.write(buf,0, len);

}

outputDoc.close();

}

catch(Exception e) { e.printStackTrace(); }

Reading file from URL and writing to file

File file = new File("D:/test123.pdf"); FileOutputStream fos = new FileOutputStream(file); BufferedOutputStream outBuf = new BufferedOutputStream(fos);

InputStream is = new URL("http://localhost:8080/pdf/test.pdf").openStream();

byte buf[]=new byte[1024]; int len; while((len=is.read(buf))>0) { outBuf.write(buf,0, len); } outBuf.close(); fos.close();