Question about Java Persistence API.

is Java Persistence API a Object-Relational Mapping Framework, or the java Programmer can use this API to do mapping between Java Applicatiion and Relational Database ??

http://java.sun.com/javaee/overview/faq/persistence.jsp

Similar Messages

Newbie question on Java Persistence API - Entity Beans

Hi All,
I am basically new to Entities and the Java Persistence API. My question is, when using a container managed EntityManager, do I have to manually tidy-up any resources? Say for example, do I have to explicitly close the database connection (if ever I have that ability)? Invoke close() on EntityManager?
- Pat

You don't have to. That's what they mean by container managed. The container does it for you.
In fact you will get an IllegalStateException if you call close on a container-managed EntityManager.

A question about Java Card API 2.2.1

Hi,I am doing my first project on java card and I have the software installed(java_card_kit-2_2_1, OCF 1.2, j2sdk1.4.1).
java_card_kit-2_2_1 include these package:
java.lang
java.io
java.rmi
javacard.framework
javacard.security
javacardx.crypto
com.sun.javacard.impl
com.sun.javacard.crypto
My question is:
How can I get the export files of the last two package:com.sun.javacard.impl and com.sun.javacard.crypto?
I really need your help and please mail to me.My email is [email protected] you very much.

Hi libin_hailang
The last two packages are not part of the api.
So, you only can use them on the Simulation.
On a real card implementation you will not find these packages.
This may be the reason for the not existing export files .
But if you need them for other purpose you can create them with the converter.
bye.

DAO pattern and Java Persistence API

Hi
This is a question for anyone who might be familiar with the standard DAO design pattern and the Java Persistence API (JPA - part of EJB3). I'm new to this technology, so apologies for any terminology aberrations.
I am developing the overall architecture for an enterprise system. I intend to use the DAO pattern as the conceptual basis for all data access - this data will reside in a number of forms (e.g. RDBMS, flat file). In the specific case of the RDBMS, I intend to use JPA. My understanding of JPA is that it does/can support the DAO concept, but I'm struggling to get my head around how the two ideas (can be made to) relate to each other.
For example, the DAO pattern is all about how business objects, data access objects, data transfer objects, data sources, etc relate to each other; JPA is all about entities and persistence units/contexts relate to each other. Further, JPA uses ORM, which is not a DAO concept.
So, to summarise - can DAO and JPA work together and if so how?
Thanks
P.S. Please let me know if you think this topic would be more visible in another forum (e.g. EJB).

Thanks, duffymo, that makes sense. However ... having read through numerous threads in which you voice your opinion of the DAO World According to Sun, I'd be interested to know your thoughts on the following ...
Basically, I'm in the process of proposing an enterprise system architecture, which will use DAO as the primary persistence abstraction, and DAO + JPA in the particular case of persistence to a RDBMS. In doing so, I'd like to illustrate the various elements of the DAO pattern, a la the standard class diagram that relates BusinessObject / DataAccessObject / DataSource / TransferObject (http://java.sun.com/blueprints/corej2eepatterns/Patterns/DataAccessObject.html). With reference to this model, I know that you have a view on the concept of TransferObject (aka ValueObject?) - how would you depict the DAO pattern in its most generic form? Or is the concept of a generic DAO pattern compromised by the specific implementation that is used (in this case JPA)?

Question about Java's HttpServer: Threading? Backlog?

Hello,
I have two questions about Java's HttpServer (com.sun.net.httpserver). From the JavaDoc:
>
Management of threads can be done external to this object by providing a Executor object. If none is provided a default implementation is used.
>
How can I get information about the default implementation in 1.6.0_13? Do you know the behavior? From my observations, the default implementation uses no Threads, meaning every request is handled in the same Thread, this results in handling the requests to the HttpServer one after another.
Is this right?
The second question is about this, also from the JavaDoc:
>
When binding to an address and port number, the application can also specify an integer backlog parameter. This represents the maximum number of incoming TCP connections which the system will queue internally. [...]
>
When setting the backlog to -1, it uses the systems default backlog. How can I determine the systems default backlog? Can some lines of Java code reveal it (there is no getBeacklog() method)? Or is it up to the Operating System (we use Redhat Linux)?
Thanks a lot for your help!
Regards,
Timo

How can I determine the systems default backlog?You can't. There is no API for that even at the C level.
Can some lines of Java code reveal itNo.
Or is it up to the Operating System (we use Redhat Linux)?Yes. Linux provides a large default. It seems to be at least 50 on most platforms. This is not something you should be worrying about.

Java Persistence API and creation of databases

Hi All
I have designed a small address book application which uses a database to store the information. I have used the new Java Persistence API to take care of my transactions and querrys with the database. This works great for one set database which is generated the first time the application runs and is used all the time.
However I would like to make it so that the user can create a new address book (database) with a different name, I am not sure how I would do this using the Java Persistence API. I know the persistence.xml file must be placed in the META-INF directory of the source, so how would I be able manipulate the file or could I place the file somewhere else.
David

I am using the Derby database. I can create a database by passing the create command when I create the entity Manager like so:
Connection c = DriverManager.getConnection("jdbc:derby:AddressBook;create=true", "app", "app");My problem is that as I understand it the persistence.xml file must know the name of the database. Unless there is another way of setting this. The line in the persistence file I am referring to is:
<property name="toplink.jdbc.url" value="jdbc:derby:AddressBook"/>I wonder if I can progamatically set this value so that I have a default database in the persistence.xml and others can then create there own.
David

Three questions about Java and Ftp

Hello, i've the following questions about Java and Ftp:
1- .netrc file is in $HOME directory but i can't access to this directory from java code. The following line producesan Exception (directory doesn't exists)
FileWriter file = new FileWriter ("$HOME/.netrc");
2- .netrc file must have the following permissions: -rw- --- --- but when i create the .netrc file the following permissions are on default: -rw- r-- r--, how can i change this permissions? (In java code, i can't use chmod.....)
3- Are there any way to pass parameters to a .netrc file? If i get to do this i needn't change the permissions because i can't modify or create/destroy this file.
Thanks in advanced!!!
Kike

1- .netrc file is in $HOME directory but i can't
access to this directory from java code. The
following line producesan Exception (directory
doesn't exists)
FileWriter file = new FileWriter ("$HOME/.netrc");$HOME would have to be replaced by a shell, I don't
think you can use it as part of a legal path.
Instead, use System.getProperty("user.home");
Ok, thanks
2- .netrc file must have the followingpermissions:
-rw- --- --- but when i create the .netrc file the
following permissions are on default: -rw- r--r--,
how can i change this permissions? (In java code,i
can't use chmod.....)Yes, you can: Runtime.exec("chmod ...");
I need to use estrictly the .netrc with -rw- --- --- permissions
Yes, i can use Runtime.exec ("chmod ..."); but i don't like very much this solution because is a slow solution, am i right?
3- Are there any way to pass parameters to a.netrc
file? If i get to do this i needn't change the
permissions because i can't modify orcreate/destroy
this file.I don't think so. Why do you need the .netrc file in
Java at all? Writing a GUI frontend?I want to use automatic ftp in a java program and FTP server, the files and path are not always the same, so i can:
- modify .netrc (for me is the complex option)
- destroy and create a new .netrc (is easier but i have permissions problem)
- use .netrc with parameters but i haven't found any help about it
Thanks for your prompt reply!!!!
Kike

Java persistence api : ejb ql

Hi,
I am using java persistence api(over oracle toplinks)
I have an entity customer and another entity contacts.
customer is mapped with contact as one to many.
the contact have a field primarycontact.
I want to get the contact name from contacts for a customer where primarycontact field is true. and set this contact name as a field customercontact which is a string in customer..
I got a way by executing multiple queries.
but is it possible to do this in single query using ejb ql?
Any help will be greatly appreciated..
Thanks in advance....

@Id
@GeneratedValue( @GeneratedValue(strategy= GenerationType.TABLE, generator="SOMENAME")
public int setId() {
returrn this.id;
in the database you need to create table using following commands
CREATE TABLE SEQUENCE
SEQ_NAME VARCHAR(50),
SEQ_COUNT DECIMAL(15)
and insert a row initally with the same "SOMENAME" like
insert into sequence values ( "SOMENAME", 1);
you can get the next id by adding 50(default) to "SELECT SEQ_COUNT FROM SEQUENCE WHERE SEQ_NAME = "SOMENAME"
hope this provides a solution.

Questions about Java Servlets and JSP

Hi,
I'm a confident Java Programmer (and really enjoy using this language) but am very new to Java servlets and Java Server Pages.
I have previously worked with Perl on my web projects (simple 'league' style voting pages). I read in my 'Core Java' book that I should no longer use perl or even cgi.
I need to know more about Java servlets and Java Server Pages so I can make the switch to a 'real' programming language.
I have a few questions:
How should I start to learn JS and JSP?
How applicable will the java knowlegdge I have already be?
Are JSP common on the world wide web?
What tools do I need to start? (I currently develop in JBuilder and have Java 1.4.1 Standard Edition)
Is it likey my web host (and others) will support JSP?
Thank-you very much for helping a novice get started,
Regards,
Paul

Hi, Steve ...has to be frustrating! But do not despair.
Let's suppose the servlet it's named MyServlet on package org.servlets
WEB-INF should look:
WEB-INF
classes
org
servlets
MyServlet.class
web.xml
web.xml file should have this two declarations:
<web-app>
<servlet>
    <servlet-name>MyServlet</servlet-name>
    <servlet-class>org.servlets.MyServlet</servlet-class>
</servlet>

<servlet-mapping>
    <servlet-name>MyServlet</servlet-name>
    <url-pattern>/MyServlet</url-pattern>
</servlet-mapping>

</web-app>Now, once the container starts (Tomcat?), you should be able to see that servlet in:
http://localhost:8080/[my-context/]MyServletAnd what my-context is? The web application context. This string should be empty if your're deploying to the root context, otherwise should the context name. In Tomcat, deploying to root context defaults to using webapps/ROOT.
Sorry for my English, but I felt the need to answer your request. I hope it helps despite my writing.

Question about Java GSS-Kerberos authentication

Hi,
I am new to GSS API. I have a client requirement to use Java GSS Kerberos Authentication instead of using IIS for Integrated Windows Authentication. In IWA, the IE browser automatically picks up the logged-in windows user credentials and passes it to IIS, which authenticates you against Active Directory and returns SUCCESS.
We are planning to write a Servlet/JSP code on Apache Tomcat on Solaris 10, which uses Java GSS API to do Kerberos Authentication and return SUCCESS to the user. When I look at the examples:
http://java.sun.com/j2se/1.4.2/docs/guide/security/jgss/tutorials/AcnOnly.html#RunAc
it says:
"You will be prompted for your Kerberos user name and password, and the underlying Kerberos authentication mechanism specified in the login configuration file will log you into Kerberos. If your login is successful, you will see the following message: Authentication succeeded!"
Does this mean that in Kerberos Authentication using Java GSS API, the user will have to enter his windows credentials for authentication? Is there a way for the credentials to be passed from Windows automatically to the API, without user intervention?
Any links detailing the procedure would be of great help.
Thanks,
shetty2k

We are having a similar requirement from our end. To make situation worst I do not even have an idea about an approach.
What are the ways that we can use windows credentials to authenticate against IIS with tomcat?
any help is greatly appreciated.
R.

Question about Java Errors

I have some questions about some java errors
1. what kind of errors are contained in Error class?
2.does this class contain only runtime errors?
3. if the question number 2 is positive, what about InstantiationError which is a compile error and is a subclass of Error.
4.When our program is out of memory, which processes are done for an error to be produced. is the error actually from OS or VM?

I have some questions about some java errors
1. what kind of errors are contained in Error class?An Error is a subclass of Throwable that indicates serious problems that a reasonable application should not try to catch.
2.does this class contain only runtime errors?No
3. if the question number 2 is positive, what about
InstantiationError which is a compile error and is a
subclass of Error.
4.When our program is out of memory, which processes
are done for an error to be produced. is the error
actually from OS or VM?Various - both, depending on where the error occurred.

Question about Java apps structure

Hello guys,
I'm a professional C++ programmer and I would like to start learning Java. I'm reading about Java from here and there and would like to ask you about how a java program is structured compared to C++.
So in C++, I have main.cpp (or any other file name, doesn't matter), which contains a the main() function, and I have .h and .cpp class files that I instantiate (basically) in my main function to get my program to work.
In Java, I'm confused and can't really find the "general" rule to how stuff are organised. I noticed that every class has a main function (why?), and there's no global scope. And "somehow", file names must exactly be equal to the class names.
The question is: how are Java files of classes (and other stuff, if available) are arranged to create a program? What's the standard why? And How can I have many classes together in a single main()?
Thank you for any efforts :-)
Edited by: 927494 on 13.04.2012 07:02
Edited by: 927494 on 13.04.2012 09:10

Thank you guys for the replies. I still have some more doubts :-)
Do I have to have a file for the implementation and a file for the definitons, like cpp and header files? or just everything inside the class?
Why does Netbeans fail to compile when I change the class name? what should I change with the class name in general to have it compile correctly? From what I understand till now, the top level class's name (the class with the main() function that's gonna be executed) has to be equal to the file name (and I got that this is the sufficient condition for the app to compile), while the same file can have more classes if I wish. Did I get that right?
I don't know if I get that right too, we pass only a SINGLE class/file to the compiler, and it automatically resolves ALLLL the included files automatically, unlike C++, where all cpp files have to be passed to the compiler/makefile to create object files, and then the executable is created after linking all those object files with the libraries together. i.e.: Java doesn't really need a makefile because making is really simple with only 1 filename. True?

Question about java-based server app frameworks

Hello, I am working on a Java applet application and would like to choose a Java-based scalable server framework to use within my applcation. I have found a few like xsocket or QuickServer and have a question about other. And, also, which is the one You may advise? Yours sincerely, Slawek

For online gaming server. I first heard of xsocket and started using this, but have the problem with NAT. I now know that I need to initiate connections from client behind NAT (server has a public IP) and send messages from server to client within the same connection. I am doing this the following way (as shown in examples- below), but it appears that server receives messages, but client doesnt. I dont listen on any ports in client application and just need to take advantage of the connection initiated (information go from client to server properly).
Server-
try{ nbc = pool.getNonBlockingConnection(inetAddress, 8090);
try{ nbc.write("|01|______|02|______|03|______|04|______|05|______|06|______|07|______|08|______|09|______|10|______"); }catch(Exception ee){}
}catch(java.io.IOException f){}
Client-
public boolean onData(INonBlockingConnection nbc) throws IOException,ClosedChannelException,BufferUnderflowException,MaxReadSizeExceededException{
String x = nbc.readStringByLength(100);
System.out.println("S >> C = "+x);

Some questions about Java deployment steps and techniques

All my java experience is coding and testing in my local machine (where, of course, a jre is available), but ... when I deploy to other people, they may not have a jre or they may have a different version of it than the one needed to run my application. I've read different stuff online including jars and java web start but still I have many questions.
(1) first one first, Sun contradicts common sense, when it says that i can redistribute my own customized light version of their jre by taking out some files (java.sun.com/j2se/1.5.0/jre/README). there are two ways for me to get a jre: Way one is by downloading one from Sun, the download comes as an *.exe file and I don't see how I can take files out of it, so do you know how?. Way two would be by simply copying the set of files i choose (according to that Readme) from my current jre installation (the one on my \java\jdk\jre directory), does this make sense?, (if you're under windows) doesn't an installed version of a jre need a couple of dlls plus some new registry entries?, this contradicts common sense, if I'm not wrong, that Readme is a nonsense, but since that readme is at each of us jre installation \java\jdk1.x\jre\Readme, it can't be a nonsense, therefore I'm wrong, therefore the answer is either Way 1 or Way 2, HOW? ... or maybe there's a Way 3?
(2) Say I never read that Readme so I download the jre (as an exe) to bundle it along with my application in a jar ... now I'll give my neighbor either a jar with two exes or two exes jars ... is there a way to make a jar so that two files get executed? ... if the answer is No and I have competition from a second neighbor, then I believe I'm asking my first neighbor to choose my application based on our friendship, that's not reasonable if we are doing business, so Java loses.
(3) Say that my application is a single executable file like this,
class X{
public static void main(String[]$$$){
System.out.println("Console, where are you?");
At this point, say that my neighbor accepted the two executables, he executed the jre.exe and has jre6 in his system, now he double clicks on my X.jar ... it's a console application and jar files are not associated with the java.exe launcher since java 5, but with javaw which doesn't open any console ... how do i make it so a console opens and prints "Console, where are you?" ... do I ask my neighbor-customer to add a couple of lines to his path and open his console and (please) enter java -jar jarfile.jar? ... isn't it too much? ... i hope i'm wrong cause this is kind of discouraging
(4) I've read that by installing a more recent version of a jre on a system that has an older jre (there to help other applications work), I might be causing a problem for the other applications to run ... I guess that's the reason why that Readme kind of encourage to redistribute a "private" version of a jre (one that doesn't come with a java.exe launcher ... any feedback on this?
(5) I'm reading a lot of hype about Java Web Start ... it looks better than the traditional jar/jre deployment ... but setting up a MIME type to *.jnlp, it doesn't come with some free hosting I've checked ... somebody can recommend a free hosting service that allows to set a *.jnlp MIME? (I'll appreciate a suggestion here, cause I would like to test Web Start)... and, anyhow, how you people compare it with the paradigm of the single executable file?.
Thanks. Your feedback is highly appreciated.

jorgelbanda wrote:
..(5) I'm reading a lot of hype about Java Web Start ... It's gratifying to think that someone who wants to deploy apps., has the common sense to search first! You would not guess how I often I hear "I wanna' make an EXE" shortly followed by "What's webstart?".
...it looks better than the traditional jar/jre deployment ... but setting up a MIME type to .jnlp, it doesn't come with some free hosting I've checked ... OK. You cannot define new mime types, but perhaps the site already has it defined. An easy way to check is to upload 'any old file' that ends in .jnlp and use the [mime type checker|http://pscode.org/mime/] to see what content type it is served as.
..somebody can recommend a free hosting service that allows to set a .jnlp MIME? (I'll appreciate a suggestion here, cause I would like to test Web Start)... I'm pretty sure the Google based sites offer it.
Note that I edited the asterisks out of your post, to avoid the forum software parsing half the reply as bold.

Java persistence API

Hi! I am trying to learn to use the http://www.devx.com/Java/Article/33650/ api manually, i tried using netbeans 6.0 for it but i'm not very sure what it does so i am going to try it manually now. I've read these 2 articles by Antonio Goncalves
(http://www.devx.com/Java/Article/33650/ && http://www.devx.com/Java/Article/33906/) it doesn't look very difficult at first but the thing is in netbeans 6.0 when i try to use the annotations,@Inheritance for example, It autocompletes but i don't see the javadoc it says ("Javadoc not found"). I already added the javaee5 documentation to the javaplataform manager but it doesn't do the trick.
Anybody can help? Also if you know any kind of tutorial for the persistence api if you could point me towards there it would be nice.
And finally sorry if i have misplaced this post, I couldn't find a better place.
Thanks, Joaquin

Hi! I am trying to learn to use the http://www.devx.com/Java/Article/33650/ api manually, i tried using netbeans 6.0 for it but i'm not very sure what it does so i am going to try it manually now. I've read these 2 articles by Antonio Goncalves
(http://www.devx.com/Java/Article/33650/ && http://www.devx.com/Java/Article/33906/) it doesn't look very difficult at first but the thing is in netbeans 6.0 when i try to use the annotations,@Inheritance for example, It autocompletes but i don't see the javadoc it says ("Javadoc not found"). I already added the javaee5 documentation to the javaplataform manager but it doesn't do the trick.
Anybody can help? Also if you know any kind of tutorial for the persistence api if you could point me towards there it would be nice.
And finally sorry if i have misplaced this post, I couldn't find a better place.
Thanks, Joaquin

Question about Java Persistence API.

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