Develop Reference

Error writing to S3 using TextIO.write() (Google Dataflow)

I have a Google Dataflow code similar to the below
import org.apache.beam.sdk.Pipeline;
import org.apache.beam.sdk.io.FileSystems;
import org.apache.beam.sdk.io.TextIO;
import org.apache.beam.sdk.io.fs.ResourceId;
import org.apache.beam.sdk.options.*;
import org.apache.beam.sdk.transforms.Create;
public class S3Test {
public static void main(String[] args) {
PipelineOptions options = PipelineOptionsFactory.fromArgs(args).withValidation().create();
Pipeline pipeline = Pipeline.create(options);
ResourceId outputDir = FileSystems.matchNewResource("s3://my-bucket/temp/", true);
pipeline
.apply("New",
Create.of("Hello World!!")
)
.apply(
"Write to S3",
TextIO.write()
.to("s3://my-bucket/test.txt")
.withoutSharding()
.withTempDirectory(outputDir)
);
pipeline.run();
}
}
This works to some extent, in that it first creates a temporary file on my S3 bucket. However, when it tries to rename it to my final desired/input filename, it throws the following error.
Receiver class org.apache.beam.sdk.io.aws.s3.S3FileSystem does not
define or inherit an implementation of the resolved method 'abstract
void rename(java.util.List, java.util.List,
org.apache.beam.sdk.io.fs.MoveOptions[])' of abstract class
org.apache.beam.sdk.io.FileSystem.
I guess I have to override or implement a rename() function, but not sure where I'd start on that.
Has anyone tried to write successfully to S3 using TextIO.write()?
EDIT:
Below is the full message in the Run window:
Dec 24, 2022 4:56:34 PM
org.apache.beam.sdk.io.WriteFiles$WriteShardsIntoTempFilesFn
processElement INFO: Opening writer
8a0dbf70-a0fc-48dd-92f9-8ff4000a8076 for window
org.apache.beam.sdk.transforms.windowing.GlobalWindow#2dddc1b9 pane
PaneInfo{isFirst=true, isLast=true, timing=ON_TIME, index=0,
onTimeIndex=0} destination null Dec 24, 2022 4:56:37 PM
org.apache.beam.sdk.io.FileBasedSink$Writer close INFO: Successfully
wrote temporary file
s3://my-bucket/temp/.temp-beam-13da7e3e-15a9-4285-a90c-30c7c6dcfe99/9e53ec6a8a0dbf70-a0fc-48dd-92f9-8ff4000a8076
Dec 24, 2022 4:56:37 PM
org.apache.beam.sdk.io.WriteFiles$FinalizeTempFileBundles$FinalizeFn
process INFO: Finalizing 1 file results Dec 24, 2022 4:56:37 PM
org.apache.beam.sdk.io.FileBasedSink$WriteOperation
createMissingEmptyShards INFO: Finalizing for destination null num
shards 1. Dec 24, 2022 4:56:37 PM
org.apache.beam.sdk.io.FileBasedSink$WriteOperation moveToOutputFiles
INFO: Will copy temporary file
FileResult{tempFilename=s3://my-bucket/temp/.temp-beam-13da7e3e-15a9-4285-a90c-30c7c6dcfe99/9e53ec6a8a0dbf70-a0fc-48dd-92f9-8ff4000a8076,
shard=0,
window=org.apache.beam.sdk.transforms.windowing.GlobalWindow#2dddc1b9,
paneInfo=PaneInfo{isFirst=true, isLast=true, timing=ON_TIME, index=0,
onTimeIndex=0}} to final location s3://my-bucket/test.txt Exception in
thread "main" org.apache.beam.sdk.Pipeline$PipelineExecutionException:
java.lang.AbstractMethodError: Receiver class
org.apache.beam.sdk.io.aws.s3.S3FileSystem does not define or inherit
an implementation of the resolved method 'abstract void
rename(java.util.List, java.util.List,
org.apache.beam.sdk.io.fs.MoveOptions[])' of abstract class
org.apache.beam.sdk.io.FileSystem. at
org.apache.beam.runners.direct.DirectRunner$DirectPipelineResult.waitUntilFinish(DirectRunner.java:374)
at
org.apache.beam.runners.direct.DirectRunner$DirectPipelineResult.waitUntilFinish(DirectRunner.java:342)
at
org.apache.beam.runners.direct.DirectRunner.run(DirectRunner.java:218)
at
org.apache.beam.runners.direct.DirectRunner.run(DirectRunner.java:67)
at org.apache.beam.sdk.Pipeline.run(Pipeline.java:323) at
org.apache.beam.sdk.Pipeline.run(Pipeline.java:309) at
com.example.S3Test.main(S3Test.java:255) Caused by:
java.lang.AbstractMethodError: Receiver class
org.apache.beam.sdk.io.aws.s3.S3FileSystem does not define or inherit
an implementation of the resolved method 'abstract void
rename(java.util.List, java.util.List,
org.apache.beam.sdk.io.fs.MoveOptions[])' of abstract class
org.apache.beam.sdk.io.FileSystem. at
org.apache.beam.sdk.io.FileSystems.renameInternal(FileSystems.java:323)
at org.apache.beam.sdk.io.FileSystems.rename(FileSystems.java:308)
at
org.apache.beam.sdk.io.FileBasedSink$WriteOperation.moveToOutputFiles(FileBasedSink.java:802)
at
org.apache.beam.sdk.io.WriteFiles$FinalizeTempFileBundles$FinalizeFn.process(WriteFiles.java:1077)

Try updating your pipeline... by default withNumShards() is set to zero, so it will write to a single file
pipeline
.apply("New",
Create.of("Hello World!!")
)
.apply(
"Write to S3",
TextIO.write()
.to("s3://my-bucket/test.txt")
.withNumShards(1)
.withTempDirectory(outputDir)
);

WebListener prevents the web application to launch

I have a Vaadin web application, that is deploying OK.
BUT when I add a FolderWatcher service as a Listener using
#WebListener
The application fails to deploy, but it starts the thread if I disable the annotation #WebListener the application does deploy.
Folder watcher class
public class FolderWatchService {
private final WatchService watcher;
private final Map<WatchKey, Path> keys;
private static final Logger LOGGER = Logger.getLogger( FolderWatchService.class.getName() );
/**
* Creates a WatchService and registers the given directory
*/
public FolderWatchService(Path dir) throws IOException {
this.watcher = FileSystems.getDefault().newWatchService();
this.keys = new HashMap<WatchKey, Path>();
walkAndRegisterDirectories(dir);
}
/**
* Register the given directory with the WatchService; This function will be called by FileVisitor
*/
private void registerDirectory(Path dir) throws IOException
{
WatchKey key = dir.register(watcher, ENTRY_CREATE, ENTRY_DELETE, ENTRY_MODIFY);
keys.put(key, dir);
}
/**
* Register the given directory, and all its sub-directories, with the WatchService.
*/
private void walkAndRegisterDirectories(final Path start) throws IOException {
// register directory and sub-directories
Files.walkFileTree(start, new SimpleFileVisitor<Path>() {
#Override
public FileVisitResult preVisitDirectory(Path dir, BasicFileAttributes attrs) throws IOException {
registerDirectory(dir);
return FileVisitResult.CONTINUE;
}
});
}
/**
* Process all events for keys queued to the watcher
*/
public void processEvents() {
for (;;) {
// wait for key to be signaled
WatchKey key;
try {
key = watcher.take();
} catch (InterruptedException x) {
return;
}
Path dir = keys.get(key);
if (dir == null) {
LOGGER.log( Level.FINE, "WatchKey not recognized!!", "" );
System.err.println("WatchKey not recognized!!");
continue;
}
for (WatchEvent<?> event : key.pollEvents()) {
#SuppressWarnings("rawtypes")
WatchEvent.Kind kind = event.kind();
// Context for directory entry event is the file name of entry
#SuppressWarnings("unchecked")
Path name = ((WatchEvent<Path>)event).context();
Path child = dir.resolve(name);
String fileContent;
// if directory is created, and watching recursively, then register it and its sub-directories
if (kind == ENTRY_CREATE) {
System.out.println("File created");
LOGGER.log( Level.FINER, "New File created", "" );
readFile(child.toString());
}
}
// reset key and remove from set if directory no longer accessible
boolean valid = key.reset();
if (!valid) {
keys.remove(key);
// all directories are inaccessible
if (keys.isEmpty()) {
break;
}
}
}
}
private static void readFile(String pathname){
try {
File file = new File(pathname);
StringBuilder fileContents = new StringBuilder((int)file.length());
Scanner scanner = new Scanner(file);
String lineSeparator = System.getProperty("line.separator");
try {
while(scanner.hasNextLine()) {
fileContents.append(scanner.nextLine() + lineSeparator);
}
String fileContent = fileContents.toString();
System.out.println("File name: "+FilenameUtils.getBaseName(pathname));
LOGGER.log( Level.FINER, "File name: "+FilenameUtils.getBaseName(pathname), "" );
String title = "File Title: "+fileContent.substring(0, 64).trim().lastIndexOf(System.getProperty("line.separator"))+"...";
} finally {
scanner.close();
}
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
ContextLister class
#WebListener
public class ContextListener implements ServletContextListener {
#Override
public void contextDestroyed(ServletContextEvent arg0) {
System.out.println("#### Folder watcher service destroyed");
}
#Override
public void contextInitialized(ServletContextEvent arg0) {
System.out.println("#### Folder watcher service initialized");
Path dir = Paths.get(PropertiesCache.getInstance().getProperty("file_input_location"));
try {
new FolderWatchService(dir).processEvents();
System.out.println("#### Folder watcher service started");
} catch (IOException e) {
System.out.println("#### Folder watcher Problem");
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
EDIT: Added what is printed out by logs
Jun 26, 2017 10:56:31 PM org.apache.catalina.core.AprLifecycleListener
lifecycleEvent
INFO: Loaded APR based Apache Tomcat Native library 1.2.12 using APR version
1.5.2.
Jun 26, 2017 10:56:31 PM org.apache.catalina.core.AprLifecycleListener
lifecycleEvent
INFO: APR capabilities: IPv6 [true], sendfile [true], accept filters
[false], random [true].
Jun 26, 2017 10:56:31 PM org.apache.catalina.core.AprLifecycleListener
lifecycleEvent
INFO: APR/OpenSSL configuration: useAprConnector [false], useOpenSSL [true]
Jun 26, 2017 10:56:31 PM org.apache.catalina.core.AprLifecycleListener
initializeSSL
INFO: OpenSSL successfully initialized (OpenSSL 1.0.2k 26 Jan 2017)
Jun 26, 2017 10:56:31 PM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["http-nio-8080"]
Jun 26, 2017 10:56:31 PM org.apache.tomcat.util.net.NioSelectorPool
getSharedSelector
INFO: Using a shared selector for servlet write/read
Jun 26, 2017 10:56:31 PM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["ajp-nio-8009"]
Jun 26, 2017 10:56:31 PM org.apache.tomcat.util.net.NioSelectorPool
getSharedSelector
INFO: Using a shared selector for servlet write/read
Jun 26, 2017 10:56:31 PM org.apache.catalina.startup.Catalina load
INFO: Initialization processed in 1392 ms
Jun 26, 2017 10:56:31 PM org.apache.catalina.core.StandardService
startInternal
INFO: Starting service Catalina
Jun 26, 2017 10:56:31 PM org.apache.catalina.core.StandardEngine
startInternal
INFO: Starting Servlet Engine: Apache Tomcat/8.5.12
Jun 26, 2017 10:56:32 PM org.apache.catalina.util.SessionIdGeneratorBase
createSecureRandom
INFO: Creation of SecureRandom instance for session ID generation using
[SHA1PRNG] took [126] milliseconds.
Jun 26, 2017 10:56:40 PM org.apache.jasper.servlet.TldScanner scanJars
INFO: At least one JAR was scanned for TLDs yet contained no TLDs. Enable
debug logging for this logger for a complete list of JARs that were scanned
but no TLDs were found in them. Skipping unneeded JARs during scanning can
improve startup time and JSP compilation time.
#### Folder watcher service initialized
The last line here is println from ContextLister, and the applic
What am I doing wrong here?

It seems that the listener implementation is blocking at new FolderWatchService(dir).processEvents();. You should run event processing in another thread (ie using a ExecutorService to submit processEvents job and maybe cancel/shutdown in contextDestroyed)

sending a cmdarray for exec to process -- hello world

Am I not sending an array of commands, "hello world ", to exec() correctly?
correct output, hello world:
thufir#mordor:~$
thufir#mordor:~$ java -jar NetBeansProjects/HelloExec/dist/HelloExec.jar
Apr 05, 2016 7:11:23 AM net.bounceme.mordor.telnet.Main run
INFO: starting..
Apr 05, 2016 7:11:23 AM net.bounceme.mordor.telnet.Telnet <init>
INFO: connecting..
Apr 05, 2016 7:11:23 AM net.bounceme.mordor.telnet.Telnet connect
INFO: connect..
Apr 05, 2016 7:11:23 AM net.bounceme.mordor.telnet.Telnet connect
INFO: [echo hello 1, echo hello 2, echo hello 3]
Apr 05, 2016 7:11:24 AM net.bounceme.mordor.telnet.Telnet connect
INFO: did process..
Apr 05, 2016 7:11:24 AM net.bounceme.mordor.telnet.Telnet connect
INFO: trying..
hello 1
Apr 05, 2016 7:11:24 AM net.bounceme.mordor.telnet.Telnet read
SEVERE: exiting.. 0
thufir#mordor:~$
code:
package net.bounceme.mordor.telnet;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;
import java.util.logging.Level;
import java.util.logging.Logger;
import static java.lang.System.out;
public class Telnet {
private final static Logger LOG = Logger.getLogger(Telnet.class.getName());
public Telnet() {
LOG.info("connecting..");
}
private List<String> getCommand() {
List<String> commands = new ArrayList<>();
commands.add("echo hello 1");
commands.add("echo hello 2");
commands.add("echo hello 3");
return commands;
}
private void read(Process process) throws IOException, InterruptedException {
BufferedReader input = new BufferedReader(new InputStreamReader(process.getInputStream()));
String line = null;
while ((line = input.readLine()) != null) {
out.println(line);
}
int exitVal = process.waitFor();
LOG.log(Level.SEVERE, "exiting.. {0}", exitVal);
}
private void connect() {
LOG.info("connect..");
Runtime runtime = Runtime.getRuntime();
List<String> cmds = getCommand();
String[] cmdArray = cmds.toArray(new String[cmds.size()]);
String command = cmdArray[0];
LOG.info(cmds.toString());
Process process = null;
try {
process = runtime.exec(command);
} catch (IOException ex) {
LOG.severe("process wrong");
Logger.getLogger(Telnet.class.getName()).log(Level.SEVERE, null, ex);
}
LOG.info("did process..");
LOG.info("trying..");
try {
read(process);
} catch (IOException | InterruptedException ex) {
LOG.severe("read wrong");
Logger.getLogger(Telnet.class.getName()).log(Level.SEVERE, null, ex);
}
}
public void tryConnect() {
connect();
}
}
crash:
thufir#mordor:~$
thufir#mordor:~$ java -jar NetBeansProjects/HelloExec/dist/HelloExec.jar
Apr 05, 2016 7:12:32 AM net.bounceme.mordor.telnet.Main run
INFO: starting..
Apr 05, 2016 7:12:32 AM net.bounceme.mordor.telnet.Telnet <init>
INFO: connecting..
Apr 05, 2016 7:12:32 AM net.bounceme.mordor.telnet.Telnet connect
INFO: connect..
Apr 05, 2016 7:12:32 AM net.bounceme.mordor.telnet.Telnet connect
INFO: [echo hello 1, echo hello 2, echo hello 3]
Apr 05, 2016 7:12:32 AM net.bounceme.mordor.telnet.Telnet connect
SEVERE: process wrong
Apr 05, 2016 7:12:32 AM net.bounceme.mordor.telnet.Telnet connect
SEVERE: null
java.io.IOException: Cannot run program "echo hello 1": error=2, No such file or directory
at java.lang.ProcessBuilder.start(ProcessBuilder.java:1048)
at java.lang.Runtime.exec(Runtime.java:620)
at java.lang.Runtime.exec(Runtime.java:485)
at net.bounceme.mordor.telnet.Telnet.connect(Telnet.java:48)
at net.bounceme.mordor.telnet.Telnet.tryConnect(Telnet.java:66)
at net.bounceme.mordor.telnet.Main.run(Main.java:17)
at net.bounceme.mordor.telnet.Main.main(Main.java:11)
Caused by: java.io.IOException: error=2, No such file or directory
at java.lang.UNIXProcess.forkAndExec(Native Method)
at java.lang.UNIXProcess.<init>(UNIXProcess.java:248)
at java.lang.ProcessImpl.start(ProcessImpl.java:134)
at java.lang.ProcessBuilder.start(ProcessBuilder.java:1029)
... 6 more
Apr 05, 2016 7:12:32 AM net.bounceme.mordor.telnet.Telnet connect
INFO: did process..
Apr 05, 2016 7:12:32 AM net.bounceme.mordor.telnet.Telnet connect
INFO: trying..
Exception in thread "main" java.lang.NullPointerException
at net.bounceme.mordor.telnet.Telnet.read(Telnet.java:30)
at net.bounceme.mordor.telnet.Telnet.connect(Telnet.java:57)
at net.bounceme.mordor.telnet.Telnet.tryConnect(Telnet.java:66)
at net.bounceme.mordor.telnet.Main.run(Main.java:17)
at net.bounceme.mordor.telnet.Main.main(Main.java:11)
thufir#mordor:~$
when trying to use cmdArray:
process = runtime.exec(cmdArray);
The reasoning:
...it's because when exec is given a single string, it parses it first
(in a way that we don't like). In contrast, when exec is given a
string array, it simply passes it on to the operating system without
parsing it.
https://stackoverflow.com/a/19383655/262852

Null Pointer Exception on Session in Hibernate Java

I am creating a simple application and for some reason I keep getting null pointer exception. My guess is that it has something to do with my session.open being inside a if statement?
The error I am getting is on the finally block where it says session.close();
import java.util.*;
import javax.persistence.*;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
public class OrderTester {
private static SessionFactory sessionFactory;
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
Session session = null;
Transaction transaction = null;
System.out.println("Press 1 to log in or press 2 to sign up");
int n = scan.nextInt();
if (n == 1) {
Customer c = new Customer();
// c.logIn();
} else if (n == 2) {
try {
sessionFactory = HibernateUtil.getSessionFactory();
session = sessionFactory.openSession();
transaction = session.beginTransaction();
Customer c = new Customer();
Address a = new Address();
session.save(c);
session.save(a);
Scanner read = new Scanner(System.in);
System.out.println("Enter a username");
String userName = read.next();
c.setUsername(userName);
System.out.println("Enter a password");
String password = read.next();
c.setPassword(password);
System.out.println("Enter the street name");
String streetName = read.next();
a.setStreetName(streetName);
System.out.println("Enter city");
String city = read.next();
a.setCity(city);
System.out.println("Enter state");
String state = read.next();
a.setState(state);
System.out.println("Enter zipcode");
String zipcode = read.next();
a.setZipCode(zipcode);
read.close();
transaction.commit();
} catch (Exception ex) {
transaction.rollback();
System.out.println("Transaction is rolled back.");
} finally {
session.close();
sessionFactory.close();
}
}
}
}
The error:
Press 1 to log in or press 2 to sign up
2
Mar 05, 2016 4:51:44 PM org.hibernate.annotations.common.reflection.java.JavaReflectionManager <clinit>
INFO: HCANN000001: Hibernate Commons Annotations {4.0.5.Final}
Mar 05, 2016 4:51:44 PM org.hibernate.Version logVersion
INFO: HHH000412: Hibernate Core {4.3.11.Final}
Mar 05, 2016 4:51:44 PM org.hibernate.cfg.Environment <clinit>
INFO: HHH000206: hibernate.properties not found
Mar 05, 2016 4:51:44 PM org.hibernate.cfg.Environment buildBytecodeProvider
INFO: HHH000021: Bytecode provider name : javassist
Mar 05, 2016 4:51:44 PM org.hibernate.cfg.Configuration configure
INFO: HHH000043: Configuring from resource: /hibernate.cfg.xml
Mar 05, 2016 4:51:44 PM org.hibernate.cfg.Configuration getConfigurationInputStream
INFO: HHH000040: Configuration resource: /hibernate.cfg.xml
Mar 05, 2016 4:51:45 PM org.hibernate.internal.util.xml.DTDEntityResolver resolveEntity
WARN: HHH000223: Recognized obsolete hibernate namespace http://hibernate.sourceforge.net/. Use namespace http://www.hibernate.org/dtd/ instead. Refer to Hibernate 3.6 Migration Guide!
Exception in thread "main" java.lang.NullPointerException
at Pizza.OrderTester.main(OrderTester.java:65)

A NullPointerException on that line with nothing else in the stack trace can only mean that session is null. The only way that could happen, as far as I can tell, is if the session = sessionFactory.openSession(); assignment is never executed - which would mean that an exception is happening either in sessionFactory.openSession() or in HibernateUtil.getSessionFactory(), with that exception being hidden by the later exception raised in the finally block.
I expect that if you step through this code in a debugger you will see the execution flow jump from one of those two lines to the catch block, then hit a NullPointerException on transaction.rollback() (because the transaction assignment never happened either) and jump to the finally block, where it hits another NullPointerException and bails out.

Since both session and sessionFactory are initialized as null outside the try/catch block, never assume they will not be null in finally clause and call close() directly. Change it to the following:
} catch (Exception ex) {
if(transaction != null) {
try {
transaction.rollback();
} catch (Exception e) { // Log error }
}
ex.printStackTrace();
System.out.println("Transaction is rolled back.");
} finally {
if(session != null) {
try {
session.close();
} catch (Exception e) { // Log error }
}
if(sessionFactory != null) {
try {
sessionFactory.close();
} catch (Exception e) { // Log error }
}
}

query for row EXIST with JPA JQL

isUnique should just check for the existence of a newsgroup and return a boolean reflecting that:
init:
Deleting: /home/thufir/NetBeansProjects/USENET/build/built-jar.properties
deps-jar:
Updating property file: /home/thufir/NetBeansProjects/USENET/build/built-jar.properties
compile:
run:
DEBUG: nntp: newsrc loading /home/thufir/.newsrc
DEBUG: nntp: newsrc load: 5 groups in 26ms
Jul 29, 2012 8:37:13 PM net.bounceme.dur.usenet.driver.Main getFolders
INFO: [gwene.com.androidcentral, gwene.com.blogspot.emacsworld, gwene.com.blogspot.googlecode, gwene.com.blogspot.googlereader, gwene.com.economist]
[EL Info]: 2012-07-29 20:37:17.607--ServerSession(20908501)--EclipseLink, version: Eclipse Persistence Services - 2.3.0.v20110604-r9504
[EL Info]: 2012-07-29 20:37:19.815--ServerSession(20908501)--file:/home/thufir/NetBeansProjects/USENET/build/classes/_USENETPU login successful
Jul 29, 2012 8:37:20 PM net.bounceme.dur.usenet.driver.Main persist
INFO: gwene.com.androidcentral
Jul 29, 2012 8:37:20 PM net.bounceme.dur.usenet.driver.Main isUnique
INFO: []
Jul 29, 2012 8:37:20 PM net.bounceme.dur.usenet.driver.Main isUnique
INFO: gwene.com.androidcentral new
Jul 29, 2012 8:37:20 PM net.bounceme.dur.usenet.driver.Main persist
INFO: gwene.com.blogspot.emacsworld
Jul 29, 2012 8:37:20 PM net.bounceme.dur.usenet.driver.Main isUnique
INFO: [gwene.com.androidcentral]
Jul 29, 2012 8:37:20 PM net.bounceme.dur.usenet.driver.Main isUnique
INFO: gwene.com.blogspot.emacsworld new
Jul 29, 2012 8:37:20 PM net.bounceme.dur.usenet.driver.Main persist
INFO: gwene.com.blogspot.googlecode
Jul 29, 2012 8:37:20 PM net.bounceme.dur.usenet.driver.Main isUnique
INFO: [gwene.com.androidcentral, gwene.com.blogspot.emacsworld]
Jul 29, 2012 8:37:20 PM net.bounceme.dur.usenet.driver.Main isUnique
INFO: gwene.com.blogspot.googlecode new
Jul 29, 2012 8:37:20 PM net.bounceme.dur.usenet.driver.Main persist
INFO: gwene.com.blogspot.googlereader
Jul 29, 2012 8:37:20 PM net.bounceme.dur.usenet.driver.Main isUnique
INFO: [gwene.com.androidcentral, gwene.com.blogspot.emacsworld, gwene.com.blogspot.googlecode]
Jul 29, 2012 8:37:20 PM net.bounceme.dur.usenet.driver.Main isUnique
INFO: gwene.com.blogspot.googlereader new
Jul 29, 2012 8:37:20 PM net.bounceme.dur.usenet.driver.Main persist
INFO: gwene.com.economist
Jul 29, 2012 8:37:20 PM net.bounceme.dur.usenet.driver.Main isUnique
INFO: [gwene.com.androidcentral, gwene.com.blogspot.emacsworld, gwene.com.blogspot.googlecode, gwene.com.blogspot.googlereader]
Jul 29, 2012 8:37:20 PM net.bounceme.dur.usenet.driver.Main isUnique
INFO: gwene.com.economist new
BUILD SUCCESSFUL (total time: 9 seconds)
From querying the database, this seems to work as advertised. However, it seems like the wrong type of query:
package net.bounceme.dur.usenet.driver;
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Logger;
import javax.mail.Folder;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.TypedQuery;
import net.bounceme.dur.usenet.model.Newsgroups;
import net.bounceme.dur.usenet.model.Usenet;
public class Main {
private static final Logger LOG = Logger.getLogger(Main.class.getName());
private Usenet u = Usenet.INSTANCE;
public static void main(String[] args) {
Main main = new Main();
}
public Main() {
List<Newsgroups> folderGroups = getFolders();
EntityManagerFactory emf;
EntityManager em;
emf = Persistence.createEntityManagerFactory("USENETPU");
em = emf.createEntityManager();
for (Newsgroups n : folderGroups) {
persist(em, n);
}
em.close();
}
private void persist(EntityManager em, Newsgroups newNewsgroup) {
LOG.info(newNewsgroup.toString());
TypedQuery<Newsgroups> query = em.createQuery("SELECT n FROM Newsgroups n", Newsgroups.class);
List<Newsgroups> results = query.getResultList();
if (isUnique(newNewsgroup, results)) {
em.getTransaction().begin();
em.persist(newNewsgroup);
em.getTransaction().commit();
}
}
private boolean isUnique(Newsgroups newNewsgroup, Iterable<Newsgroups> results) {
LOG.info(results.toString());
for (Newsgroups existingNewsgroup : results) {
if ((existingNewsgroup.getNewsgroup().equals(newNewsgroup.getNewsgroup()))) {
return false;
}
}
LOG.info(newNewsgroup + "\tnew");
return true;
}
private boolean queryDB2(EntityManager em, Newsgroups ng) {
String newsgroup = ng.getNewsgroup();
TypedQuery<Newsgroups> query = em.createQuery("SELECT n FROM Newsgroups n WHERE n.newsgroup = :newsgroup", Newsgroups.class);
Newsgroups result = query.getSingleResult();
LOG.info("query result:\n" + result + "\ncompared to\n" + ng);
return false;
}
private List<Newsgroups> getFolders() {
List<Folder> folders = u.getFolders();
List<Newsgroups> newsgroups = new ArrayList<>();
for (Folder folder : folders) {
Newsgroups newsgroup = new Newsgroups(folder);
newsgroups.add(newsgroup);
}
LOG.info(newsgroups.toString());
return newsgroups;
}
}
Where rather than using isUnique to iterate through the query result, what would be the syntax for a match?
I see that in SQL there's an EXISTS key word. How can I turn the isUnique method into just a query for existence?

You can try simple query as:
SELECT 1
FROM Newsgroups n
WHERE newNewsgroup = 'newNewsgroup'
LIMIT 1;