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- 2
- Java client-server: what options are there?This is an issue that I have been pondering and investigating
for years, and I wish there was a book, chapter or URL that
covered it.
I have to develop client-server systems in which the following
is pretty much decided:
- The database is Oracle 9iR2
- The server OSs are Solaris and Linux
- The clients (a few dozen) are Windows (XP?)
- The client side runs on Java
Those are the givens, the rest is up for grabs...
The main undecided part is: exactly how to realize the client-server
connection? That's what I would like to hear and read about.
What options do I have?
To get the ball rolling, I will share my experiences so far.
First, I tried the JDBC approach, with a standalone application.
There was a stored procedure in the server, and it was called
from the client. The cons were: the size of the JDBC being much
larger than my app, and there was also the issue of performance.
I feel that I should move more of the functionality and heavy duty
processing to the server side, where I can have plenty of horsepower.
My second attempt was a Java applet which got its data
through CGI-BIN from an OCI C program running on the server.
The performance was pretty good and I'd like to stick with
the OCI part but not with CGI-BIN.
I just began the third approach: using SSH. The server part
is a given since it comes ready in Linux, and I got the Java
client part from sshtools.com.
I have read about servlets, Tomcat, etc. but it looks like once
I get into that stuff (the area seems to be called "Enterprise"),
the tools become extremely expensive (for instance I will have
to upgrade my $700 Developer JBuilder to a $3500 Enterprise JBuilder).
The issue of performance still worries me (I am a speed freak):
I wish I could just use the Unix R-commands (rsh, etc.) so all
the encrypting-decrypting doesn't get in the way of client
performance (my app is Intranet in a trusted environment) but
I guess I can live with the more modern, secure, etc., SSH.
Thanks very much for sharing your expert insight on this,
(and if you are a writer deciding on a topic, I'll bet that
this one will sell a lot of books! - anyone from O'Reilly
out there?)
-Ramon F Herrera
- 2
- type safety in java 1.5 (bug or hole?)"John C. Bollinger" <email***@***.com> schrieb im Newsbeitrag
news:c8g89n$esu$email***@***.com...
> It would all the same be a nice complement to generics if the 1.5
> compiler would indeed issue warnings about user-inserted casts that are
> not provably correct. (I.e. those that the compiler cannot simply
> ignore). That would give Bracha's comment (that started this confusion)
> broad enough scope to no longer be confusing.
I agree very much.
BTW, there's another comment from Bracha in the very same paper that's
confusing (me): He says "The Java virtual machine does not directly support
overriding of methods with different return types. This feature is supported
by the compiler.". What does this mean? Does this mean that the different
return types are gone at run time? Here's an example:
static class A {
static A create() { return new A(); }
public A m(A a) { System.out.println("A->A"); return a; }
}
static class B extends A {
static B create() { return new B(); }
public B m(A a) { System.out.println("A->B"); return (B) a; }
public B m(B b) { System.out.println("B->B"); return b; }
}
public void testOverriding() {
A a_a = A.create(); // static type A, dynamic type A
A a_b = B.create(); // static type A, dynamic type B
B b_b = B.create(); // static type B, dynamic type B
A a2 = a_a.m(a_b); // prints: A->A
A a3 = a_a.m(b_b); // prints: A->A
A a5 = a_b.m(a_b); // prints: A->B <== overriding works
A a6 = a_b.m(b_b); // prints: A->B <== overriding works
B b2 = b_b.m(a_b); // prints: A->B
B b3 = b_b.m(b_b); // prints: B->B
}
public void testReflection() {
try {
System.out.println(
B.class.getMethod("m", new Class[] {A.class}).getReturnType()
== B.class
); // prints: true <== reflection works, too
}
catch (Throwable t) {
throw new RuntimeException("Laufzeitfehler", t);
}
}
So there's obviously some runtime support for overriding methods with a
different return type, because in this example both the overriding and the
reflection worked. Then what did Bracha mean?
2004-05-24, York.
--
werres at uni minus bremen.de
http://www.uni-bremen.de/~werres
- 8
- 'back engineering' java appletshi,
is it possible to gain access to java code by a user using an applet over
the web? i know with some scripting languages like PHP or javascript then
users can view the code and 'back engineer' it to discover how it works etc.
is this possible with java?
thanks
- 8
- butting components right up against each otherOn Fri, 27 Jun 2003 13:29:59 GMT, Roedy Green <email***@***.com> wrote:
> On Fri, 27 Jun 2003 14:06:22 +0100, Daniel Dyer
> <email***@***.com> wrote or quoted :
>
>> Sorry, I didn't mean ipadx/ipady, that won't help. You certainly
>> shouldn't need to use absolute positioning though. Do you have any
>> sample code to show us?
> I just wanted to put a string of JTextFields with black backgrounds
> right against each other so they look like one continuous field.
Have you tried setting the borders on the text fields to null? Maybe it's
the borders that make it look like there's a gap. Have you tried a
different layout (maybe try GridLayout, just to see if it looks the same,
it's much simpler so it will be easier to spot if you've done something
wrong).
Dan.
--
Daniel Dyer
Empathy Software (http://www.empathysoftware.com)
-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 80,000 Newsgroups - 16 Different Servers! =-----
- 8
- XML Validation problemI am having alot of trouble getting a XML document validated with a
schema.
I got a sample document and schema off of w3schools.com, which passed
an online xml validator:
http://tools.decisionsoft.com/schemaValidate.html. I cannot, however,
get them validated programmatically.
The documents are:
node.xsd:
<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.w3schools.com"
xmlns="http://www.w3schools.com"
elementFormDefault="qualified"><xs:element name="note">
<xs:complexType>
<xs:sequence>
<xs:element name="to" type="xs:string"/>
<xs:element name="from" type="xs:string"/>
<xs:element name="heading" type="xs:string"/>
<xs:element name="body" type="xs:string"/>
</xs:sequence>
</xs:complexType>
</xs:element></xs:schema>
node.xml:
<?xml version="1.0"?>
<note
xmlns="http://www.w3schools.com"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3schools.com note.xsd">
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
I'm using java 1.5 currently, although I had problems with 1.4 and
xerces, so I'm pretty confident the problem isn't related to the java
version.
My code is:
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setIgnoringElementContentWhitespace(true);
factory.setIgnoringComments(true);
SchemaFactory sFact =
SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
factory.setSchema(sFact.newSchema(new java.io.File(SCHEMA_FILE)));
DocumentBuilder builder = factory.newDocumentBuilder();
builder.setErrorHandler(new ErrorHandler() {
public void warning (SAXParseException exception) throws SAXException
{
System.err.println(exception);
}
public void error (SAXParseException exception) throws SAXException {
System.err.println(exception);
}
public void fatalError (SAXParseException exception) throws
SAXException {
System.err.println(exception);
}
});
org.w3c.dom.Document doc = builder.parse(file);
The error I recieve is:
org.xml.sax.SAXParseException:
http://www.w3.org/TR/xml-schema-1#cvc-elt.1?note
org.xml.sax.SAXParseException:
http://www.w3.org/TR/xml-schema-1#cvc-elt.1?note
Exception in thread "main" java.lang.IllegalStateException
at com.sun.org.apache.xerces.internal.jaxp.validation.ValidatorHandlerImpl$3.checkState(ValidatorHandlerImpl.java:411)
at com.sun.org.apache.xerces.internal.jaxp.validation.ValidatorHandlerImpl$3.getElementTypeInfo(ValidatorHandlerImpl.java:441)
at com.sun.org.apache.xerces.internal.jaxp.JAXPValidatorComponent$SAX2XNI.elementAug(JAXPValidatorComponent.java:299)
at com.sun.org.apache.xerces.internal.jaxp.JAXPValidatorComponent$SAX2XNI.endElement(JAXPValidatorComponent.java:291)
at com.sun.org.apache.xerces.internal.jaxp.XNI2SAX.endElement(XNI2SAX.java:163)
at com.sun.org.apache.xerces.internal.jaxp.validation.XNI2SAXEx.endElement(XNI2SAXEx.java:108)
at com.sun.org.apache.xerces.internal.impl.xs.XMLSchemaValidator.endElement(XMLSchemaValidator.java:818)
at com.sun.org.apache.xerces.internal.jaxp.validation.ValidatorHandlerImpl.endElement(ValidatorHandlerImpl.java:339)
at com.sun.org.apache.xerces.internal.jaxp.XNI2SAX.endElement(XNI2SAX.java:163)
at com.sun.org.apache.xerces.internal.jaxp.JAXPValidatorComponent.endElement(JAXPValidatorComponent.java:206)
at com.sun.org.apache.xerces.internal.xinclude.XIncludeHandler.endElement(XIncludeHandler.java:790)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanEndElement(XMLDocumentFragmentScannerImpl.java:1241)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDispatcher.dispatch(XMLDocumentFragmentScannerImpl.java:1685)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:368)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:834)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:764)
at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:148)
at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(DOMParser.java:248)
at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:292)
at javax.xml.parsers.DocumentBuilder.parse(DocumentBuilder.java:169)
...
I am behind a web proxy, and I don't know if the validation process
involves retrieving files at the URLs in the xml and xsd files, which
could be the problem.
can someone shed some light on this?
Thanks in advance.
- 12
- How to control the cursor positon of java program in console mode?I am writing a small database that requires user input.
However, whenever something is output to the screen, the cursor stays at the
beginning of the output instead of the end of the output.
How can I let it go to the end of the output?
For example:
say, the output is like this:
This is a database. Please input your information below.
prompt:>
I want the cursor to go to after the ">" sign but it stays in front of
"this" although whenever the user presses the keyboard it goes the end after
">".
This is not a big problem but makes my application look not so professional.
Anyway to cure this?
John
- 12
- DB Selection - J2MEHi,
I am developing an application for PDAs using IBMs
VM (J9). Now my problem is, that I want to store
data on the device. Well, I am using J2ME with
Personal Profile to do this, so file support is
present in this configuration. Now I wonder if
there exist solutions to store data and easily
retrieve it. (commercial, free, open source)
I have to store data on the device, add new
data often, update and delete old data sometimes.
1. So how do you store data, when not having present
a complete RDBMS?
2. There are RDBMS for this platform too.
Any experiences using them?
(for example Pointbase)
3 There is this JDO Option (for example
with ObjectDB) is this working well?
4. What do you think of the following options,
which I already found, but have no idea
whether they will work?
I alread checked:
-JDMB (rather minimalistic, only key/value pairs to be saved)
-JISP (produces rather big files -> not suitable for
constrained devices?)
-HSQL (Anybody got that to work within the mentioned configuration?
I think mainly the java.sql.* classes are missing in the
personal profile)
-ObjectDB (OODB with JDO, no idea exactly if this will
work for my purposes)
Any help will be appreciated
Rene
- 12
- using parameterized ArrayListI am trying to read write <Event> objects to an ArrayList ... but when
I try to convert the arraylist back to the object arrayit gives me a
ClassCastException for the line
return (Event[]) a.toArray();
--------------------------------------
BufferedReader ois = null;
ArrayList<Event> a = new ArrayList<Event>();
try {
ois = new BufferedReader(new FileReader(this.calFile));
Event e = null;
String line;
while ((line = ois.readLine()) != null) {
e = new Event(line);
a.add(e);
}
ois.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ParseException e) {
e.printStackTrace();
} catch (InvalidTimeRangeException e) {
e.printStackTrace();
}
if (a.isEmpty())
return null;
return (Event[]) a.toArray();
- 14
- JTable and associating objects with nodesHi,
Does anyone know how to store objects in a name value pair data structure
(i.e. hashmap) in a JTable? It easy to store the name of the object but to
store the object with the name, I am not sure.
Any help would be great
Thanks
Bob
- 14
- Eclipse: browsing sourcecode using { as marksHello everyone,
I am using eclipse 3.0.2 on Linux. Is it possible to browse
Java-sourcecode using the brackets { as a jumping point?
example
public void foo(){ <- first entry
if(isFoo){ <- second entry
doFoo();
}else{ <- third entry
doAnotherFoo();
}
thanks alot for any help!
kind regards
Oliver
- 15
- gui builder for javaHi,
I just started programming java and I am looking for a free gui builder for
java on linux or windows platforms. Where can I find it.
thanks
Johan
- 15
- newbie: Global EJB and more ...
Hi group,
While thinking of how to transfer a tranditional client-server app
into J2EE, I got following two questions:
1, In a typical application, there should be some global (even
singleton) objects which are created on application startup code and
stay there until the program exiting. In the idiom of J2EE, what kind
of Beans act like this kind of global object? And, when and how these
global beans should be created?
2, I knew Beans have to be deployed onto the server before they come
to be available, but those Beans quit often need some objects to
complete its job, these objects may encapsulate a algorithem, may do
some management task, but they typically dont have to exposed to
client tire or web tire. I call these objects are intermediate
objects. My question is, should this kind of objects need to be a EJB?
My J2EE books seems only to mention three kinds of Beans,
SessionBeans, EntityBeans and MessageBeans. But what do I do for those
intermediate objects?
Thanks in advance.
--
email***@***.com
%% (fortunes)
Q: How did you get into artificial intelligence?
A: Seemed logical -- I didn't have any real intelligence.
- 16
- Applets and J2SE 5.0 - problems?I set my IE browser (corporate edict to use IE...ugh)
to use the 9/30 FCS release of 5.0
Whenever I visit a page with an applet, the browser
crashes.
Someone at our local user group (www.javasig.com)
mentioned something about version mismatches (???).
Anyone else experience this?
btw, kudos to Calvin Austin (J2SE 5.0 spec lead) and
the rest for a very organized and efficient release.
Frank G.
+==========================================+
| Crossroads Technologies Inc. |
| www.CrossroadsTech dot com |
| fgreco at REMOVE!cross!roads!tech!dot com|
+==========================================+
- 16
- Unicode value of a characterHi,
I am a beginner in Java programming and I would like to know which
code ( program ) I must write to get the Unicode value of any
character ?
Thank you very much for your help !
JPR105.
- 16
- "Invalid column name" inserting a row with weblogic/oracle
bsaastad wrote:
> Hello,
>
>
>
> Environment
>
> Weblogic 8.1, Oracle 9.0.1, JDK1.4
>
>
>
> I am attempting to migrate from WLS 6.1 to WLS 8.1. All appears to work
> with the exception of database inserts. They ALWAYS fail and return an
> "ORA-00904: invalid column name". I am connecting to the database via a
> pooled data source. This code worked fine under WLS6.1 using the
> Weblogic JDriver. The JDriver performs the inserts under 8.1 but the
> Statement.executeBatch() command returns a 0-length int[] (an
> acknowledged bug in the JDriver.) BEA says to use the drivers supplied
> by Oracle. I have tried both the type 4 driver and the type 2 oci
> driver with exactly the same result.
Odd. Would you pleaes download the latest appropriate version of
oracle's driver and either run this code in a standalone program
getting your connection directly from the driver, or get the driver
to the front of the -classpath argument in the startWeblogic script,
and then run this code in the server again?
thanks,
Joe Weinstein at BEA
>
>
>
> I can query the database via the connection and dump the contents of the
> queried row along with the column names using the ResultMetaData.
>
>
>
> ex.
>
>
>
> ResultSet rs = stmt.executeQuery( sqlCmd );
>
> ResultSetMetaData rsmd = rs.getMetaData();
>
> System.out.println( "Results of '" + sqlCmd + "'");
>
> while ( rs.next() )
>
> {
>
> for( int i = 1; i <= rsmd.getColumnCount(); i++)
>
> {
>
> System.out.println( "'" + rsmd.getColumnName(i) +
> "=" + rs.getString( i ) + "' " );
>
> }
>
> }
>
>
>
> .. produces:
>
>
>
> Results of 'SELECT POOL_ID, POOL_NM, POOL_DESC, REV_BY, REV_DT FROM
> POOL_R WHERE POOL_ID = 11'
>
>
>
> 'POOL_ID=11'
>
> 'POOL_NM=COMM'
>
> 'POOL_DESC=Communications Servers'
>
> 'REV_BY=saastabp'
>
> 'REV_DT=2002-12-16'
>
>
>
> Then when I turn around and try to insert a row like this:
>
>
>
> String sqlCmd = "INSERT INTO POOL_R (POOL_ID, POOL_NM, POOL_DESC,
> REV_BY, REV_DT) VALUES (100, 'FRED', 'TEST POOL NAME FOR FRED', 'test-
> user', {ts '2003-10-24 16:00:26.703'})";
>
>
>
> System.out.println( "[" + sqlCmd + "]");
>
> stmt.executeUpdate( sqlCmd);
>
>
>
> .. I get the exception below. Has anyone seen this before? Any ideas?
>
>
>
> Thanks,
>
> -Brian
>
>
>
> [INSERT INTO POOL_R (POOL_ID, POOL_NM, POOL_DESC, REV_BY, REV_DT) VALUES
> (100, 'FRED', 'TEST POOL NAME FOR FRED', 'test-user', {ts '2003-10-24
> 16:00:26.703'})]
>
>
>
> java.sql.SQLException: ORA-00904: invalid column name
>
>
>
>
>
> at weblogic.rjvm.BasicOutboundRequest.sendReceive(BasicOutbound-
> Request.java:108)
>
>
>
> at weblogic.rmi.internal.BasicRemoteRef.invoke(BasicRemoteRef-
> .java:138)
>
>
>
> at weblogic.jdbc.rmi.internal.StatementImpl_weblogic_jdbc_wrapp-
> er_Statement_oracle_jdbc_driver_OracleStatement_811_WLStub.exec-
> uteUpdate(Unknown Source)
>
>
>
> at weblogic.jdbc.rmi.internal.StatementStub_weblogic_jdbc_rm-
> i_internal_StatementImpl_weblogic_jdbc_wrapper_Statement_ora-
> cle_jdbc_driver_OracleStatement_811_WLStub.executeUpdate(Unk-
> nown Source)
>
>
>
> at weblogic.jdbc.rmi.SerialStatement_weblogic_jdbc_rmi_internal-
> _StatementStub_weblogic_jdbc_rmi_internal_StatementImpl_weblogi-
> c_jdbc_wrapper_Statement_oracle_jdbc_driver_OracleStatement_811-
> _WLStub.executeUpdate(Unknown Source)
>
>
>
> at com.billing.tm.persist.BatchTest.doInsert(BatchTest.java:93)
>
>
>
> at com.billing.tm.persist.BatchTest.main(BatchTest.java:185)
>
>
>
> Caused by: java.sql.SQLException: ORA-00904: invalid column name
>
>
>
>
>
> at oracle.jdbc.dbaccess.DBError.throwSqlException(DBError-
> .java:134)
>
>
>
> at oracle.jdbc.ttc7.TTIoer.processError(TTIoer.java:289)
>
>
>
> at oracle.jdbc.ttc7.Oall7.receive(Oall7.java:579)
>
>
>
> at oracle.jdbc.ttc7.TTC7Protocol.doOall7(TTC7Protocol.java:1894)
>
>
>
> at oracle.jdbc.ttc7.TTC7Protocol.parseExecuteFetch(TTC7Protocol-
> .java:1094)
>
>
>
> at oracle.jdbc.driver.OracleStatement.executeNonQuery(OracleSta-
> tement.java:2132)
>
>
>
> at oracle.jdbc.driver.OracleStatement.doExecuteOther(OracleStat-
> ement.java:2015)
>
>
>
> at oracle.jdbc.driver.OracleStatement.doExecuteWithTimeout(Orac-
> leStatement.java:2877)
>
>
>
> at oracle.jdbc.driver.OracleStatement.executeUpdate(OracleState-
> ment.java:858)
>
>
>
> at weblogic.jdbc.wrapper.Statement.executeUpdate(Statement-
> .java:328)
>
>
>
> at weblogic.jdbc.rmi.internal.StatementImpl_weblogic_jdbc_wrapp-
> er_Statement_oracle_jdbc_driver_OracleStatement.executeUpdate(U-
> nknown Source)
>
>
>
> at weblogic.jdbc.rmi.internal.StatementImpl_weblogic_jdbc_wrapp-
> er_Statement_oracle_jdbc_driver_OracleStatement_WLSkel.invoke(U-
> nknown Source)
>
>
>
> at weblogic.rmi.internal.BasicServerRef.invoke(BasicServerRef-
> .java:466)
>
>
>
> at weblogic.rmi.internal.BasicServerRef$1.run(BasicServerRef-
> .java:409)
>
>
>
> at weblogic.security.acl.internal.AuthenticatedSubject.doAs(Aut-
> henticatedSubject.java:353)
>
>
>
> at weblogic.security.service.SecurityManager.runAs(SecurityMana-
> ger.java:144)
>
>
>
> at weblogic.rmi.internal.BasicServerRef.handleRequest(BasicServ-
> erRef.java:404)
>
>
>
> at weblogic.rmi.internal.BasicExecuteRequest.execute(BasicExecu-
> teRequest.java:30)
>
>
>
> at weblogic.kernel.ExecuteThread.execute(ExecuteThread.java)
>
>
>
> at weblogic.kernel.ExecuteThread.run(ExecuteThread.java:170)
>
>
> --
> Posted via http://dbforums.com
|
| Author |
Message |
korcs
|
 Posted: 2007-9-19 21:48:00 |
Top |
java-programmer, data lost issue using sockets
Hi,
I have an interesting issue with socket programming.
I would like to send String based information via Sockets.
As it could happen, that a part of the information gets lost on its
way to the client, I would like to send before all such packages the
size of the package as a "short" value (or something equal, but not
string because you can never be sure that your string completely
arrived ).
Does anybody know what is an elegant solution for this problem?
I send the strings using:
PrintWriter out = new PrintWriter(client.getOutputStream(), true);
out.println("test");
Thanks,
korcs
|
| |
|
| |
|
|
| Posted: 2007-9-19 22:15:00 |
Top |
java-programmer >> data lost issue using sockets
> As it could happen, that a part of the information gets lost on
> its
> way to the client, I would like to send before all such packages > the
> size of the package as a "short" value (or something equal, but
> not
> string because you can never be sure that your string completely
> arrived ).
You should investigate why you are "losing" data first. Instead
of trying to put some custom checks of your own in there.
Tcp should be doing that for you. If you are "losing" data, then
you will proably "lose" some of your custom checks too, then
are you going to add more custom checks for your custom checks?
Try explaining how you are "losing" your data first.
|
| |
|
| |
|
korcs
|
| Posted: 2007-9-19 22:54:00 |
Top |
java-programmer >> data lost issue using sockets
On 19 Sep., 16:14, derek wrote:
> > As it could happen, that a part of the information gets lost on
> > its
> > way to the client, I would like to send before all such packages > the
> > size of the package as a "short" value (or something equal, but
> > not
> > string because you can never be sure that your string completely
> > arrived ).
>
> You should investigate why you are "losing" data first. Instead
> of trying to put some custom checks of your own in there.
> Tcp should be doing that for you. If you are "losing" data, then
> you will proably "lose" some of your custom checks too, then
> are you going to add more custom checks for your custom checks?
>
> Try explaining how you are "losing" your data first.
I send an xml structure to a client.
This structure has of course an opening and an ending tag but the body
of the xml structure can have different lengths.
So I thought it is better to make sure that the client side knows in
advance, which size it should receive and if there was some bug during
the data transfer to know that the received xml struct is too big or
too small.
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| Posted: 2007-9-19 23:07:00 |
Top |
java-programmer >> data lost issue using sockets
If that is all you are sending, then dont bother with telling the other side how big it is. You could just close the socket on your end when you are done. The other end will read the data until no more data is available then process it. If there is more data after the xml, then you do need to have some agreement by which you both know where one piece of data ends and one starts. Either preface it with a length as you originally stated, or you could use a special character to signify the end of one data and the beginning of another. The choice between the two options would depend on the type of data you are sending. If you decide to use a special character, just make sure that it doesnt class with the actual data you are sending.
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Roedy Green
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| Posted: 2007-9-20 0:09:00 |
Top |
java-programmer >> data lost issue using sockets
On Wed, 19 Sep 2007 06:47:56 -0700, korcs <email***@***.com>
wrote, quoted or indirectly quoted someone who said :
>As it could happen, that a part of the information gets lost on its
>way to the client, I would like to send before all such packages the
>size of the package as a "short" value (or something equal, but not
>string because you can never be sure that your string completely
>arrived ).
TCP/IP guaranteed accurate delivery through checksums and packet
resends.
If you used a DataInputStream you could use writeUTF which prepends
each string with a 16-bit length field. see
http://mindprod.com/jgloss/jgloss/utf.html#WRITEUTF
You could prepend each field with the 32-bit length in bytes after
encoding. If you start reading the string as a byte array, TCP will
automatically block till the whole thing is available.
See http://mindprod.com/jgloss/encoding.html
--
Roedy Green Canadian Mind Products
The Java Glossary
http://mindprod.com
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Filip Larsen
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| Posted: 2007-9-20 4:52:00 |
Top |
java-programmer >> data lost issue using sockets
korcs wrote:
> I would like to send String based information via Sockets.
>
> As it could happen, that a part of the information gets lost on its
> way to the client, I would like to send before all such packages the
> size of the package as a "short" value (or something equal, but not
> string because you can never be sure that your string completely
> arrived ).
You don't mention how you read the data back in, but a common mistake
that gives the behaviour you seem to observe, is to fail to read the
socket in a loop until all expected data has been read (like getting end
of file or n bytes or characters) as most Java input read methods do not
guarantee that they will read "the full block" like some of the
readFully methods do. For instance, this apply when using a Reader
subclass to read data into a character array.
Regards,
--
Filip Larsen
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| Posted: 2007-9-20 10:41:00 |
Top |
java-programmer >> data lost issue using sockets
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Index ‹ java-programmer |
- Next
- 1
- JTable and optimal column width.Hi!
I have a JTable which has to columns filled over an 'String[][]'. Is it
possible, to set the cell width to the longest value in an column?
I found a solution with String.lengt() over Google, but this doesn't work
correctly because the value of String.length() doesn't fit exactly. I think
this is because the proportional fonts.
Greetings,
Christian.
- 2
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buttons. These buttons go dim when the mouse is over them. When clicked,
another image appears on a different part of the page (I built this using
the Set Nav Bar image function). This all works fine on my Mac, using my
browser safari and Internet Explorer. But on a PC using Internet Explorer
the rollovers dim but when clicked nothing happens. Does anybody know why?
I can paste the code if that helps anybody . I'm not too good at
understanding Java script code so let me know what bits might help
Thanks
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I am trying to submit a form onUnLoad when the user accidentally
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transaction.
On IE, this works fine.
But on Netscape or Mozzilla browsers, the form would simply not submit
when
the browser is closed.
here is the code.
<script language="JavaScript">
function CheckWindowClosed() {
document.MyForm.submit();
}
</script>
<body onLoad="FunctionHandler();" onUnload="CheckWindowClosed();">
Kindly let me know if there is any workaround or fix where I can get
this working on Netscape.
Thanks and Regards,
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- 5
- ServerSocket & multiple clientsNeed help please.
I am trying to write a small client-server application that uses a
ServerSocket that allows connection of two clients via two ports (one on each
port, say 3000 & 4000).
I've tried different techniques, but always get the first client working but
the second client waiting until after the first client has ended (see code
snippet below).
How should I approach this (without the use of threads)?
(I am using the loopback address of "127.0.0.1" as both clients are on the
same PC)
private ServerSocket ss1;
private ServerSocket ss2;
private Socket socket1;
private Socket socket2;
try
{
ss1 = new ServerSocket(3000);
ss2 = new ServerSocket(4000);
}
and then
socket1 = ss1.accept();
socket2 = ss2.accept();
- 6
- Problem with Session Beans stateHi, I'm currently making a session bean, which will eventually act as
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I have implemented the bean so that it just accepts a string (which
will eventually be an object reference), and the user can add and
remove strings.
Unfortunately, if I access the same bean from another machine and
create an instance of the session bean, they are shown the same
contents as from the other machine.
The session bean type is set to stateful (and I have tried stateless).
Can anyone point me in the direction of the problem please?
Cheers,
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- 7
- The server encountered an internal error () that prevented itHi All
I am using Developing a Spring Framework MVC application step-by-step
from www.springframework.org. I use apache-tomcat-5.5.23, Ant 1.6 and
jdk1.4.
when i used ant, ant deploy, ant list and ant build the these all
commands
give me message suceessful but when i write url(http://localhost:8080/
springapp/hello.htm) on the browser then I am getting the following
error. do you have solution for this problem.
type Exception report
message
description The server encountered an internal error () that prevented
it from fulfilling this request.
exception
org.apache.jasper.JasperException: /WEB-INF/jsp/hello.jsp(1,1) The
absolute uri: http://java.sun.com/jstl/core cannot be resolved in
either web.xml or the jar files deployed with this application
org.apache.jasper.compiler.DefaultErrorHandler.jsp
Error(DefaultErrorHandler.java:40)
org.apache.jasper.compiler.ErrorDispatcher.dispatc
h(ErrorDispatcher.java:407)
org.apache.jasper.compiler.ErrorDispatcher.jspErro
r(ErrorDispatcher.java:88)
org.apache.jasper.compiler.Parser.processIncludeDi rective(Parser.java:
340)
org.apache.jasper.compiler.Parser.parseIncludeDire ctive(Parser.java:
373)
org.apache.jasper.compiler.Parser.parseDirective(P arser.java:485)
org.apache.jasper.compiler.Parser.parseElements(Pa rser.java:1557)
org.apache.jasper.compiler.Parser.parse(Parser.jav a:127)
org.apache.jasper.compiler.ParserController.doPars
e(ParserController.java:212)
org.apache.jasper.compiler.ParserController.parse( ParserController.java:
101)
org.apache.jasper.compiler.Compiler.generateJava(C ompiler.java:156)
org.apache.jasper.compiler.Compiler.compile(Compil er.java:296)
org.apache.jasper.compiler.Compiler.compile(Compil er.java:277)
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org.apache.jasper.JspCompilationContext.compile(Js
pCompilationContext.java:564)
org.apache.jasper.servlet.JspServletWrapper.servic
e(JspServletWrapper.java:299)
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315)
org.apache.jasper.servlet.JspServlet.service(JspSe rvlet.java:265)
javax.servlet.http.HttpServlet.service(HttpServlet .java:803)
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rceView.renderMergedOutputModel(InternalResourceVi ew.java:97)
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render(AbstractView.java:250)
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render(DispatcherServlet.java:928)
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doDispatch(DispatcherServlet.java:705)
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method parse(Ljava/io/InputStream;Lorg/xml/sax/helpers/DefaultHandler;)V not found
This method is definitely in the latest xerces jar, so I'm guessing
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Unfortunately I have little control over the production server, so
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- I am having trouble with OJB and locking when adding things that have cascading relationshipsHi all, I am using OJB and I can't seem to add a record to the
database if that object contains another object that is a) mapped in
the mapping and b) not already in the mapping. The error I get is:
OJB works reliably in all the other test suits:
-- adding any object and not imposing any connections, ie, they have
no elements that need to cascade
-- retreiving results (either with a criteria or alll records)
I dont know whats going on and would appreciate som ehelp - thanks in
advance
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Time: 2.674
There was 1 error:
1) testAddProjectWithExistingEmployer(com.joshlong.portfolio.bos.tests.PortfolioTest)com.joshlong.portfolio.PortfolioException:
org.odmg.LockNotGrantedException: Can not lock ID:0Finished:Mon Nov 10
04:02:34 PST 2003
Started:Mon Nov 10 04:02:34 PST 2003
Title:Foo Bar
Employer:
------------------------
public void testAddProjectWithNewEmployer()
throws Exception {
// the pk for the Employer class is id and I didnt
//set it -- I want OJB to add it as well as add the Employer
//which also doesnt have the pk set which I presume makes it
// add it as opposed to updating it ...
Employer employer = new Employer();
employer.setContactInfo("this is the contact info");
employer.setName("le nom - " + new Date());
employer.setDuties("a;b;c;d");
portfolio.addEmployer(employer); // see below fo rthe code
behind addEmployer ( Employer);
Employer e = portfolio.getEmployerByName(name);
Project project = new Project();
project.setEmployer(employer);
project.setDescription("This is a description of the
things.");
project.setFinished(new Date());
project.setStarted(new Date());
project.setName("Joshua Long");
portfolio.addProject(project);
}
addEmployer is basically just a more specific method that in turn
calls:
void addRecord ( Object record )
throws PortfolioException
{
Implementation i = OJB.getInstance();
Database db = i.newDatabase();
db.open("default", Database.OPEN_READ_WRITE);
Transaction txc = i.newTransaction();
txc.begin();
txc.lock(record, Transaction.WRITE);
txc.commit();
db.close() ;
}
- 11
- Sessionhandling with Apache AxisHello Group,
i 've already written a littlr webservice with Apache Axis.
My Service starts a thread to process some data. The Client may
Access the output via different functions.
Everything very fine.
But if i kick the Client and the Session times out after 30
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I want to tell the Service to kick the Thread after a timeout,
maybe this should possible via a Session.
How can i find out if a Session is timed out?
Thanks for your help and a happy x-mas (ok ok, some days to early :-) )
Greetings,
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- 12
- JCE - load key from stringHi All,
We're trying to use JCE to encrypt some data. The issue is key storage.
We want to store it in some database, so the question is how to
re-create the key for decryption from varchar2 column?
The key in string form looks like this:
cryptix.jce.provider.key.RawSecretKey@3bfce353
This can be stored in the database easily. But how to load this into
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TIA
Michael
- 13
- tomcat/applet question...this is really weird, in tomcat/webapps/<appName>I have a jsp AND an
applet.. I'm using a package called smack for writing jabber clients
(http://www.jivesoftware.org/smack/), so:
in jsp:
<%@ page import="org.jivesoftware.smack.*"%>
no problems...
in applet:
import org.jivesoftware.smack.*;
when try to compile get told this package doesn't exist...
package is where all packages are supposed to be in Tomcat
(C:\tomcat\common\lib) and, again, the jsp has no problems with it, but
the applet, which is in exact same location as jsp, for some reason
can't find it..
(in applet am even getting en error (identifier expected) on
system.out.println()... don't know what to make of this..
this is line: System.out.println("test");...)
weird thing is, if I hide System.out.println() line get told package
smack doesn't exist.. if I don't hide System.out.println() line get
ONLY identifier-expected error on System.out.println() line..
would appreciate any help... thank you.. Frances
- 14
- Quick help needed. Code runs, but one problem cannot be solvedHey, guys. I designed this code for guessing numbers.
The program should pick a random number between 1 and 10, inclusive
both. Then repeatedly prompt the user to guess the number. On each
guess report to the user that he or she is correct or that the guess is
high or low. Continue accepting guesses until the user guesses
correctly or choose to quit. Count the number of guesses and report
that value when the user guesses correctly. At the end of each game,
prompt to determine whether the user wants to play again. Continue
playing games until the user chooses to stop
Here is the problem, I let the random number print, so I know what
number is it. But when I input that number, instead of showing up
"Congratulations...", it shows up the correct number I entered is too
high. Please let me know what is going on. Thank you
//Code started!
import java.util.Random;
import java.util.Scanner;
public class HighLow
{
//
// Plays the Hi-Lo guessing game with the user
//
public static void main(String[] args)
{
boolean done = false;
boolean playAgain = true;
Random numberGenerator = new Random();
int randomNumber, numberOfGuesses, userNumber;
Scanner scan = new Scanner(System.in);
//
// Constants for messages to the user
//
final String guessMessage = "Enter your guess (-1 to quit): ";
final String tooHigh = "Sorry, the number you entered is higher than
my number.";
final String tooLow = "Sorry, the number you entered is lower than my
number.";
final String justRight = "Congratulations! You guessed my number!";
final String playAgainMessage = "Play again?";
while (playAgain) {
//
// Pick a random number
//
randomNumber = numberGenerator.nextInt(10) + 1;
System.out.println("The correct number is " +randomNumber);
//
// Start the guessing game
//
System.out.print(guessMessage);
userNumber = scan.nextInt();
numberOfGuesses = 1;
if (userNumber > randomNumber)
{
System.out.println(tooHigh);
numberOfGuesses += 1;
}
if (userNumber <0 && userNumber!=-1)
{
System.out.println("1-10 only");
}
if (userNumber < randomNumber && userNumber > 0)
{
System.out.println(tooLow);
numberOfGuesses += 1;
}
if (userNumber == randomNumber)
{
System.out.println(justRight);
numberOfGuesses += 1;
System.out.println("It taks you " +numberOfGuesses+ " times to
guess right");
}
//
// Check to see if the user wants to stop guessing
//
if (userNumber == -1)
done = true;
//
// Check to see if the user wants to play again
//
System.out.print("Would you like to play again? (y/n)? ");
if (scan.next().equals("n"))
playAgain = false;
else
done = false;
} // while loop
System.out.println("Thanks for playing! Bye!" );
} //method main
} //class HiLoGame
- 15
- XPathAPI(node, xpathStr) & XPathContext.getDTMHandleFromNode(node) slowHello,
I am using xalan 2.7.0: http://xml.apache.org/xalan-j/
As I run XPathAPI.eval(node, xpathStr) over and over again on several
nodes, it gets slower and slower.
This is documented in the XPathAPI documentation, and it suggests to
use the low-level XPath API:
http://xml.apache.org/xalan-j/apidocs/org/apache/xpath/XPathAPI.html
I am now using the low-level XPath API as follows:
XPathContext xpathSupport = new XPathContext();
PrefixResolverDefault prefixResolver = new
PrefixResolverDefault(document);
XPath xpath = new XPath(xpathStr, null, prefixResolver,
XPath.SELECT, null);
and then, for each node:
int ctxtNode = xpathSupport.getDTMHandleFromNode(contextNode);
XObject object = xpath.execute(xpathSupport, node,
prefixResolver);
It gets a bit better, but still, after using over and over again on
several nodes, it gets slower and slower.
I think that the problem is that
XPathContext.getDTMHandleFromNode(child) does not free memory.
Test this simplistic example yourself:
++++++++++++++++++++++++++++++++++++++++++++
import org.w3c.dom.*;
import javax.xml.parsers.*;
import javax.xml.transform.*;
import javax.xml.transform.dom.*;
import org.apache.xpath.*;
import org.apache.xml.utils.*;
public class Test {
public static void main(String[] argv) throws Exception {
int numChilds = 100000+1;
System.out.println("Building a document with " + numChilds + "
childs");
Document doc =
DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument();
Element root = doc.createElement("root");
doc.appendChild(root);
for (int i = 0; i < numChilds; i ++) {
Element child = doc.createElement("child");
root.appendChild(child);
Element subChild = doc.createElement("sub-child");
child.appendChild(subChild);
Element subSubChild = doc.createElement("sub-sub-child");
subChild.appendChild(subSubChild);
subSubChild.setAttribute("title", "title" + i);
}
XPathContext xpathSupport = new XPathContext();
PrefixResolverDefault prefixResolver = new
PrefixResolverDefault(doc);
XPath titleXpath = new XPath("sub-child/sub-sub-child/@title",
null, prefixResolver, XPath.SELECT, null);
Runtime r = Runtime.getRuntime();
System.out.println("Evaluating XPath for each " + numChilds +
" childs");
NodeList nodeList = root.getChildNodes();
int size = nodeList.getLength();
for (int i = 0; i < size; i++) {
long start = System.currentTimeMillis();
Element child = (Element) nodeList.item(i);
int ctxtNode = xpathSupport.getDTMHandleFromNode(child);
//String title = titleXpath.execute(xpathSupport,
ctxtNode, prefixResolver).toString();
long duration = System.currentTimeMillis() - start;
if (i < 10 || (i % (numChilds/10)) == 0)
System.out.println("child #" + i + "\t took " +
duration + " ms." +
"\tfreeMemory: " + r.freeMemory() +
"\ttotalMemory: "+r.totalMemory());
else if (i == 10)
System.out.println("printing some selected childs only
from now on...");
}
}
}
++++++++++++++++++++++++++++++++++++++++++++
Here you can see an example of the result:
$ java Test
Building a document with 100001 childs
Evaluating XPath for each 100001 childs
child #0 took 77 ms. freeMemory: 10642840 totalMemory:
45129728
child #1 took 1 ms. freeMemory: 10583848 totalMemory:
45129728
child #2 took 0 ms. freeMemory: 10583848 totalMemory:
45129728
child #3 took 0 ms. freeMemory: 10583848 totalMemory:
45129728
child #4 took 0 ms. freeMemory: 10583848 totalMemory:
45129728
child #5 took 0 ms. freeMemory: 10583848 totalMemory:
45129728
child #6 took 0 ms. freeMemory: 10583848 totalMemory:
45129728
child #7 took 1 ms. freeMemory: 10583848 totalMemory:
45129728
child #8 took 0 ms. freeMemory: 10583848 totalMemory:
45129728
child #9 took 0 ms. freeMemory: 10583848 totalMemory:
45129728
printing some selected childs only from now on...
child #10000 took 3 ms. freeMemory: 10980392 totalMemory:
45129728
child #20000 took 5 ms. freeMemory: 9976808 totalMemory:
45129728
child #30000 took 7 ms. freeMemory: 6332656 totalMemory:
45129728
child #40000 took 9 ms. freeMemory: 5112168 totalMemory:
45129728
child #50000 took 12 ms. freeMemory: 1373472 totalMemory:
45129728
child #60000 took 14 ms. freeMemory: 19851264 totalMemory:
66650112
child #70000 took 16 ms. freeMemory: 16515832 totalMemory:
66650112
child #80000 took 19 ms. freeMemory: 15040280 totalMemory:
66650112
child #90000 took 21 ms. freeMemory: 7435744 totalMemory:
66650112
child #100000 took 24 ms. freeMemory: 17416944 totalMemory:
66650112
++++++++++++++++++++++++++++++++++++++++++++
each time I call xpathSupport.getDTMHandleFromNode(child) it does not
free the memory,
and so it gets slower and slower.
How to solve this problem?
Some people has suggested to use the DOM4J package instead of Xalan.
However, we already have quite a lot of software using Xalan and
changing the code would have some cost.
Is it possible to solve this problem without discarding xalan?
Regards,
DAvid
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