Java Solutions: 2018

Wednesday, December 19, 2018

NetBeans: Cannot locate java installation in specified jdkhome

When I was trying to launch the NetBeans, I got the following message.

It happened after I updated java from jdk1.8.0_25 to jdk1.8.0_191.

I did the following to get rid of this message.

1. Open the C:\Program Files\NetBeans 7.4\etc\netbeans.conf

2. Search the file for "jdkhome" to locate the line
netbeans_jdkhome="C:\Program Files\Java\jdk1.8.0_25"

3. Change it to netbeans_jdkhome="C:\Program Files\Java\jdk1.8.0_191"

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Wednesday, November 21, 2018

Java server and client are in different timezones: Convert Timestamp / time to ZonedDateTime for comparison

If you are comparing a Timestamp from a remote server located in a different timezone with a local Timestamp, you need to convert either the remote Timestamp to a local one or vice versa.

You need to know your server's timezone id no matter which way you are going to convert. Let's say your server's timezone id is "America/New_York". (You can get all the available timezone ids by calling TimeZone.getAvailableIDs().)

1. Convert a remote Timestamp to a local ZonedDateTime

String remoteZoneId = "America/New_York";

TimeZone remoteTimeZone = TimeZone.getTimeZone(serverZoneId);

Timestamp remoteTimestamp = <the value to be converted>

//Firstly, create a ZonedDateTime representing the remote Timestamp

GregorianCalendar remoteCalendar = new GregorianCalendar(remoteTimeZone);

remoteCalendar.setTimeInMillis(remoteTimestamp.getTime());

ZonedDateTime remoteZDT = remoteCalendar.toZonedDateTime();

// ( OR use the following code to get the remote ZonedDateTime:

// Instant remoteInstant = Instant.ofEpochMilli(remoteTimestamp.getTime());
// ZonedDateTime remoteZDT = remoteInstant.atZone(remoteTimeZone.toZoneId());
// )

//Secondly, convert this remote ZonedDateTime to a local ZonedDateTime

TimeZone localTimeZone = TimeZone.getDefault();

ZonedDateTime remoteZonedResult;

if (remoteTimeZone.getRawOffset() == localTimeZone.getRawOffset()){

remoteZonedResult = remoteZDT;

} else {

remoteZonedResult = remoteZDT.withZoneSameInstant(localTimeZone.toZoneId());

}

2. Convert a local Timestamp to a local ZonedDateTime

Timestamp localTimeStamp = <your local time stamp>

TimeZone localTimeZone = TimeZone.getDefault();

ZonedDateTime localZonedResult = ZonedDateTime.of(localTimeStamp.toLocalDateTime(), localTimeZone.toZoneId());

3. Comparing

remoteZonedResult.isBefore(localZonedResult);

remoteZonedResult.isAfter(localZonedResult);

remoteZoneResult.equals(localZonedResult);

Of course, you can also convert the local Timestamp to a remote ZonedDateTime, and then comparing it with the remote ZonedDateTime representing a remote Timestamp.

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Monday, November 12, 2018

Crystal Reports: Retrieve a license key from a local machine

1. Open the SAP Crystal Reports console.

2. Click at the Help on the top menu and select License Manager

3. Write down the first part of the Existing key codes that is displayed somewhere you can reference later.

4. Click at the Window icon at the bottom-left corner of your computer monitor, type regedit, and open the regedit.

5. In the Registry Editor window, select the HKY_LOCAL_MACHINE in the left panel.

6. Type Ctrl+F to open the Find window. In the Find what slot, type the part of key code that you have saved in step 3. Click the Find Next button. The search may take some time to accomplish.

7. After the search finishes, read the complete license key from the right panel of the Registry Editor.

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Friday, September 14, 2018

NetBeans: Checkout a project with a certain tag from git

Before starting, make a copy of your current project, and store it somewhere.

Method A

1. In NetBeans, right click on the project, select Git, then Checkout, and then Checkout Files.

2. In the popped up Checkout Selected Paths window, check the Update Index with Entries from the Selected Revision: checkbox.

3. Click on the Select button. In the popped up Select Revision window, expand the Tags folder, select the tags you want to checkout, and click the Select button at the bottom.

Method B

1. In NetBeans, right click on the project, select Git, then Repository Browser.

2. In the Git Repository Browser pane, expand the Tags folder under your project, right click on the tag you would like to checkout, and select Checkout Revision.

After you have done with the tag, right click on the project again, select Git, then Checkout, and then Checkout Files. In the popped up window, click the Checkout button to checkout the HEAD of the project. And then replace your project folder with the copy you made at the beginning.

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Tuesday, August 7, 2018

ORA-01034: ORACLE not available / ORA-27101: shared memory realm does not exist

Your java program throws such an exception:

Stack Trace:
java.sql.SQLException: Listener refused the connection with the following error:
ORA-12505, TNS:listener does not currently know of SID given in connect descriptor

at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:673)
at oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:715)
at oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:385)
at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:30)
at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:564)
at java.sql.DriverManager.getConnection(DriverManager.java:664)
at java.sql.DriverManager.getConnection(DriverManager.java:247)
at com.xxx.dbase.DB.connectToDB(DB.java:111)

Caused by: oracle.net.ns.NetException: Listener refused the connection with the following error:
ORA-12505, TNS:listener does not currently know of SID given in connect descriptor

at oracle.net.ns.NSProtocolStream.negotiateConnection(NSProtocolStream.java:272)
at oracle.net.ns.NSProtocol.connect(NSProtocol.java:263)
at oracle.jdbc.driver.T4CConnection.connect(T4CConnection.java:1360)
at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:486)

When you try to log into sqlplus, you received these messages:

>$ sqlplus mydatabaseID/mydatabasePWD

SQL*Plus: Release 11.2.0.1.0 Production on Tue Aug 7 13:48:22 2018

Copyright (c) 1982, 2009, Oracle. All rights reserved.

ERROR:
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
Linux-x86_64 Error: 2: No such file or directory
Process ID: 0
Session ID: 0 Serial number: 0

Enter user-name:

After looking into the system, it turns out that the root user has filled all the space and the system has no space available for oracle users. The problem is fixed by removing some of the files and contents from the system.

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Tuesday, July 31, 2018

Solved - How to link an activated business license to your free personal TeamViewer?

You have installed a free version of TeamViewer on your computer for personal uses, but now you want to use it for business purposes. You have already had a business license and want to use it in your TeamViewer.

1. Launch and login to your TeamViewer.

2. Click the Connection on the top menu and select Open Management Console...

3. At your Management Console website, click your account icon in the top-right corner and select Edit Profile.

4. Click on the License on the left side of your profile. Click the Activate License to Account on the right site and enter your business license.

5. Enter your business license and click the Upgrade & Logout button.

6. Logout and log back in to your TeamViewer.

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Tuesday, July 3, 2018

GC overhead limit exceeded

The error, GC overhead limit exceeded, happens when the JVM is spending too much time doing garbage collection and not much memory is recovered. If the JVM spends more than 98% of its time doing GC and less than 2% of the heap memory is recovered, it will throw such an error. This means the speed of GC cannot catch up with the speed the heap memory being filled, resulting in the CPU is spending all its time with GC and no actual work is done; applications normally takes only milliseconds will now take minutes to finish.

You need to check your application to programmatically release whatever the memory it can after a process is done.

You can increase the heap size by setting the minimum and maximum memories

-Xms128m -Xmx800m

You can also use parallel garbage collections.

-XX:ParallelGCThreads=20 or -XX:+UseParallelGC

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Tuesday, June 26, 2018

Git Gui: Move a file from the Staged Changes area back to the Unstaged Changes list

After you saved your changes, you launch the Git Gui to commit your changes to the version control system.

You click the Stage Changed button to move the files from the Unstaged Changes to the Staged Changes (Will Commit) area.

Now, you noticed that there is a file you don't want to commit to the version control system. To move it back to the Unstaged Changes area, select the file in the Staged Changes area, click on the Commit in the top menu and select Unstage From Commit.

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Sunday, June 17, 2018

How to delete a youtube playlist

1. Login to your youtube account and click on the playlist you want to delete.

2. Click on the Edit at the bottom right of the screen.

3. Click at the menu icon appearing as three vertically-aligned dots and select Delete playlist.

4. Click the "Yes, delete it" button.

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Thursday, June 14, 2018

[Solved] How to automatically play YouTube video repeatedly

A. Use YouTube Loop option

The simplest way is to play the YouTube video in a modern web browser, while it is playing, right-click on the video and select Loop.

If you don't see the Loop option or the above method failed to loop, you can try the methods below.

B. Redirect the video to a repeatedly playing website

1. Open the YouTube video that you want to play repeatedly

2. Change the URL from

https://www.youtube.com/watch?v=A3yCcXgbKrE
to
youtuberepeat.com/watch?v=A3yCcXgbKrE
Then
press Enter

3. It will redirect you to the website below where you can play it repeatedly

If you use the Chrome browser, you can add a repeat button to your chrome tool bar by clicking the "Add to Chrome" located at the top-right corner of this website:

https://chrome.google.com/webstore/detail/listen-on-repeat-youtube/pgjcgpbffennccofdpganblbjiglnbip?hl=en

And acknowledge the warning message. Once you open the YouTube video you want to play repeatedly, click the repeat button located right next to the address bar, shown in the picture below denoted by the red arrow, it will automatically redirect you to the repeatedly playing website.

C. Create a playlist containing only this video

1. Open your YouTube video, click the Add to button at the bottom of the video and select Create new playlist.

2. Enter a name for the playlist. choose if you want the playlist to be public or private, then click Create.
3. Open the playlist by click the icon of three stacked horizontal lines denoted by the red arrow in the picture below and select the name of playlist you have just created in step 2.

4. Click the Play all button to play the video.

5. Click the Repleat playlist icon indicated by the red arrow in the picture below to play the video repleatly.

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Wednesday, June 13, 2018

java.sql.SQLRecoverableException: IO Error: The Network Adapter could not establish the connection hostname

You got the following error when you run your program

java.sql.SQLRecoverableException: IO Error: The Network Adapter could not establish the connection
at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:673)
at oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:715)
at oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:385)
at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:30)
at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:564)
at java.sql.DriverManager.getConnection(DriverManager.java:664)
at java.sql.DriverManager.getConnection(DriverManager.java:247)
...
Caused by: oracle.net.ns.NetException: The Network Adapter could not establish the connection
at oracle.net.nt.ConnStrategy.execute(ConnStrategy.java:445)
at oracle.net.resolver.AddrResolution.resolveAndExecute(AddrResolution.java:464)
at oracle.net.ns.NSProtocol.establishConnection(NSProtocol.java:594)
at oracle.net.ns.NSProtocol.connect(NSProtocol.java:229)
at oracle.jdbc.driver.T4CConnection.connect(T4CConnection.java:1360)
at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:486)
... 9 more
Caused by: java.net.ConnectException: Connection refused (Connection refused)
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at oracle.net.nt.TcpNTAdapter.connect(TcpNTAdapter.java:162)
at oracle.net.nt.ConnOption.connect(ConnOption.java:133)
at oracle.net.nt.ConnStrategy.execute(ConnStrategy.java:411)
... 14 more

Check the followings are correct:

1. the database URL
2. the database port
3. username and password are correct and granted the privilege for the operation
4. the host name is correct in the listener.ora and tnsnames.ora files. They are located at $ORACLE_HOME/netowrk/admin.
5. Check if the listener is running using the command: lsnrctl START

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How to start the Oracle listener and check if it is running on linux?

To start the Oracle listener:

1. Login and go to the Oracle home

cd $ORACLE_HOME or cd oracle_home_directory

2. Run the command: lsnrctl START or $ORACLE_HOME/bin/lsnrctl START

$> lsnrctl STARTLSNRCTL for Linux: Version 12.1.0.2.0 - Production on 13-JUN-2018 11:02:11
Copyright (c) 1991, 2014, Oracle. All rights reserved.
Starting /12c/app/oracle/product/12.1.0/db_1/bin/tnslsnr: please wait...
TNSLSNR for Linux: Version 12.1.0.2.0 - ProductionSystem parameter file is /12c/app/oracle/product/12.1.0/db_1/network/admin/listener.oraLog messages written to /12c/app/oracle/diag/tnslsnr/myserver_jxs/listener/alert/log.xmlListening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=196.223.1.2)(PORT=1521)))Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC1521)))
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=196.223.1.2)(PORT=1521)))STATUS of the LISTENER------------------------Alias LISTENERVersion TNSLSNR for Linux: Version 12.1.0.2.0 - ProductionStart Date 13-JUN-2018 08:56:06Uptime 0 days 2 hr. 11 min. 6 secTrace Level offSecurity ON: Local OS AuthenticationSNMP OFFListener Parameter File /12c/app/oracle/product/12.1.0/db_1/network/admin/listener.oraListener Log File /12c/app/oracle/diag/tnslsnr/myserver_jxs/listener/alert/log.xmlListening Endpoints Summary... (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=myserver_jxs)(PORT=1521))) (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC1521)))Services Summary...Service "cs" has 1 instance(s). Instance "cs", status UNKNOWN, has 1 handler(s) for this service...The command completed successfully

To check if the Oracle listener is running:

1. Repeat step 2 above

$> lsnrctl STARTLSNRCTL for Linux: Version 12.1.0.2.0 - Production on 13-JUN-2018 11:02:11Copyright (c) 1991, 2014, Oracle. All rights reserved.TNS-01106: Listener using listener name LISTENER has already been started

2. Run: $ORACLE_HOME/bin/tnsping $ORACLE_SID or tnsping database_name

$> tnsping $ORACLE_SID
TNS Ping Utility for Linux: Version 12.1.0.2.0 - Production on 13-JUN-2018 10:57:52
Copyright (c) 1997, 2014, Oracle. All rights reserved.
Used parameter files:
/12c/app/oracle/product/12.1.0/db_1/network/admin/sqlnet.ora
Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = cs)))
OK (10 msec)

3. Run lsnrctl STATUS

$> lsnrctl STATUS
LSNRCTL for Linux: Version 12.1.0.2.0 - Production on 13-JUN-2018 11:07:12
Copyright (c) 1991, 2014, Oracle. All rights reserved.
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=localhost)(PORT=1521)))
STATUS of the LISTENER
------------------------
Alias LISTENER
Version TNSLSNR for Linux: Version 12.1.0.2.0 - Production
Start Date 13-JUN-2018 08:56:06
Uptime 0 days 2 hr. 11 min. 6 sec
Trace Level off
Security ON: Local OS Authentication
SNMP OFF
Listener Parameter File /12c/app/oracle/product/12.1.0/db_1/network/admin/listener.ora
Listener Log File /12c/app/oracle/diag/tnslsnr/myserver_jxs/listener/alert/log.xml
Listening Endpoints Summary...
(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=myserver_jxs)(PORT=1521)))
(DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC1521)))
(DESCRIPTION=(ADDRESS=(PROTOCOL=tcps)(HOST=myserver_jxs)(PORT=5500))(Security=(my_wallet_directory=/12c/app/oracle/admin/cs/xdb_wallet))(Presentation=HTTP)(Session=RAW))
Services Summary...
Service "cs" has 1 instance(s).
Instance "cs", status READY, has 1 handler(s) for this service...
Service "csXDB" has 1 instance(s).
Instance "cs", status READY, has 1 handler(s) for this service...
The command completed successfully

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Wednesday, May 30, 2018

Access is denied when ending a task from the task manager

When a program becomes non-responding and you want to kill it, you right click on your task manager to run it as an administrator, find the project, clicked the End Task button and acknowledged the warning message to stop it, you get the following.

You are stuck and is not able to use your program to do anything.

To solve it,

1. Go to the detail tab of your task manager to find the PID of the program.

2. Open your Command Prompt as administrator by right click on it and run as administrator. You can also find the PID of your programs by running the command: tasklist

3. Run the command taskkill as below.

If the above does not work for your, logout and re-login or reboot your computer should solve the problem.

However, the problem still exits even after you have tried to log out and back in and reboot your computer, you may need to restore your computer to a time when it worked.

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Wednesday, May 23, 2018

USB device not recognized: The last USB device you connected to this computer malfunctioned and Windows does not recognize it

You get this message popped up on your screen.

Once you click on it, you see the window below

To fix it, open the control panel and click to open the Device Manager

In the Device Manager window, right click on the Unknown USB Device (Device Descriptor Request Failed), select Uninstall device and acknowledge the warning message to uninstall it. Restart your computer, Windows will reinstall the device automatically.

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Saturday, May 19, 2018

[Solved] Problem Ejecting USB Mass Storage Device: Windows cannot stop your 'Volume' device because a program is still using it

When you try to safely remove your external drive, you get the following message.

You can try the following methods to solve this problem. Among these methods, B and D have always worked for me :)

A. End the program using your external drive through the task manager.

1. Press Ctrl-Alt-Delete at the same time to open the task manager, select the Detail tab, click on the program that is using your external drive. If you cannot identify a program that is using your external drive, select explorer.exe. And then click on the End task button to stop it. If you have selected explorer.exe, continue to finish steps 2 and 3.

2. Click on File in the top menu of the task manager and select Run New Task.

3. Enter Explorer.exe in the popup window and click the OK button.

B. Change the drive letter

1. Open your control panel, go to Control Panel\System and Security\Administrative Tools and open the Computer Management.

2. Right-click on the external drive you want to remove, and select Change Drive Letter and Paths.

3. Select a new and not used letter for this drive and acknowledge the warning message.

4. If you want to continue using the original letter, change it back before you eject your external drive.

C. Clean the clipboard

If you have copied anything from your external drive, chances are that it is still in your clipboard which is like a temporary memory. To clear your clipboard, copy anything that is not part of your external drive or press the print screen key to replace the content in your clipboard.

D. Set your external drive to be removable.

1. Open your Windows Explorer, right-click on your external drive and choose Properties.

2. In the popup window, select the Hardware tab. Click to select your external drive and then click the Properties button.

3. Click the Change settings button in the new popup window.

4. In the new popup window, select the Policies tab and check the Quik Removeal radio button, which will allow you to remove your external drive safely without using the Safely Remove Hardware notification.

5. Click the OK button on all the windows to close them.

Of course, log out and log back in can always help. I hope that you don't need to go so far to shut down your computer. Then, of course, you can unplug the external drive without asking for any permission.

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