Archive for the ‘Java 8’ Category
SQL Developer JDK
In my classes, we use a VMware Linux install with SQL Developer. One of my students called me in a panic after an upgrade of packages when SQL Developer failed to launch. The student was astute enough to try running it from the command line where it generates an error like:
Oracle SQL Developer Copyright (c) 2005, 2018, Oracle and/or its affiliates. All rights reserved. /opt/sqldeveloper/sqldeveloper/bin/../../ide/bin/launcher.sh: line 954: [: : integer expression expected The JDK (/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.222.b10-0.fc30.x86_64/) is not a valid JDK. The JDK was specified by a SetJavaHome directive in a .conf file or by a --setjavahome option. Type the full pathname of a JDK installation (or Ctrl-C to quit), the path will be stored in /home/student/.sqldeveloper/19.2.0/product.conf Error: Unable to get APP_JAVA_HOME input from stdin after 10 tries |
The error is simple, the SQL Developer package update wipe clean the configuration of the SetJavaHome variable in the user’s ~/.sqldeveloper/19.2.0/product.conf file. The fix is three steps because its very likely that the Java packages were also updated. Here’s how to fix it:
- Navigate to the directory where you’ve installed the Java Virtual Machine (JVM) and find the current version of the JVM installed:
cd /usr/lib/jvm ls java*
It will return a set of files, like:
java java-1.8.0 java-1.8.0-openjdk java-1.8.0-openjdk-1.8.0.252.b09-0.fc30.x86_64 java-openjdk jre jre-1.8.0 jre-1.8.0-openjdk jre-1.8.0-openjdk-1.8.0.252.b09-0.fc30.x86_64 jre-openjdk
- Navigate to your user’s product configuration file with this command:
cd ~/.sqldeveloper/19.2.0
- Add the following line to the
product.conffile:# SetJavaHome /path/jdk SetJavaHome /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.252.b09-0.fc30.x86_64/
Now, you should be able to run it from the command line. The shortcut icon should also work if one was installed. Also, don’t forget to update your $JAVA_HOME variable in the master Bash resource file, or your local user’s .bashrc files.
As always, I hope this helps those looking for a quick solution.
MySQL 8.0.20 JDBC
In April, when I updated from MySQL 8.0.17 to MySQL 8.0.19, I found that my Java connection example failed. That’s because of a change in the JDBC driver, which I blogged about then. Starting yesterday, I began updating a base Fedora 30 configuration again to MySQL 8.0.20. I wrote a testing program for the Java JDBC file last time, and when I ran it this time it told me that I didn’t have the JDBC driver installed, or in the $CLASSPATH. My Java diagnostic script, MySQLDriver.java, returned the following error message:
Error: Could not find or load main class MySQLDriver |
The Java JDBC test program code is in the prior post. It simply loads the user, password, database, host, and port statically for my student image, which you can update for your MySQL deployment.
You can find the MySQL 8.0 Connector/J installation in Chapter 4 of the MySQL Connector/J 8.0 Developer Guide. The link to page where you can download the Connector/J driver is in Chapter 4, but to save time you can click on the following download link. You’ll find Ubuntu, Debian, SUSE Enterprise Linux Server, Red Hat Enterprise Linux/Oracle Linux, Fedora, Platform Independent, and Source Code at that download link.
I downloaded Fedora 30, 31, and 32 because eventually they get deprecated and sometimes I need the deprecated versions. Since Python 2.7 is deprecated, keeping an old Fedora 30 with both Python 2.7 and 3.7 is very attractive as a developer, keeping these Java libraries is also a potential convenience. On the Fedora 30 platform, you should download:
mysql-connector-java-8.0.20-1.fc30.noarch.rpm |
You install the RPM package with the following syntax:
rpm -ivh mysql-connector-java-8.0.20-1.fc30.noarch.rpm |
It installs a single mysql-connector-java.jar file in the /usr/share/java directory. Then, you need to export the Java Archive file like so in your .bashrc file:
# Set the Java CLASSPATH path. export CLASSPATH=/usr/share/java/mysql-connector-java.jar:. |
Now, my MySQLDriver Java program returned:
Cannot connect to database server: The server time zone value 'MDT' is unrecognized or represents more than one time zone. You must configure either the server or JDBC driver (via the 'serverTimezone' configuration property) to use a more specifc time zone value if you want to utilize time zone support. |
As qualified in the prior post, it required me to add the following line to my /etc/my.cnf configuration file, which synchronizes the database’s timezone with the operating system.
# Synchronize the MySQL clock with the computer system clock. default-time-zone='+00:00' |
You need to restart the MySQL Daemon to apply the change, like:
sudo systemctl restart mysqld.service |
Then, running my MySQL Driver connection test program worked like a charm. It returns the following:
Database connection established MySQLDriver Version [8.0.20] Database connection terminated |
As always, I hope this helps those looking for a quick solution.
SQL Developer Error
It’s been a couple releases trying to fix the following error thrown by SQL Developer on Fedora 30 and shown as the following dialog:
When you click the Detail button it shows the following error stack:
java.lang.NoClassDefFoundError: javafx/embed/swing/JFXPanel at oracle.dbtools.raptor.javafx.ui.JFXPanelFactory.createJFXPanelImpl(JFXPanelFactory.java:58) at oracle.dbtools.raptor.javafx.ui.JFXPanelFactory.createJFXPanel(JFXPanelFactory.java:34) at oracle.dbtools.raptor.startpage.StartPageViewer.createGUIComponent(StartPageViewer.java:179) at oracle.dbtools.raptor.startpage.StartPageViewer.getEditorContent(StartPageViewer.java:136) at oracle.ide.editor.AsynchronousEditor$2.run(AsynchronousEditor.java:345) at oracle.ide.editor.AsynchronousEditor$5.run(AsynchronousEditor.java:555) at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1443) at org.netbeans.modules.openide.util.GlobalLookup.execute(GlobalLookup.java:68) at org.openide.util.lookup.Lookups.executeWith(Lookups.java:303) at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2058) Caused by: java.lang.ClassNotFoundException: javafx.embed.swing.JFXPanel cannot be found by oracle.sqldeveloper_19.2.0 at org.eclipse.osgi.internal.loader.BundleLoader.findClassInternal(BundleLoader.java:501) at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:421) at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:412) at org.eclipse.osgi.internal.baseadaptor.DefaultClassLoader.loadClass(DefaultClassLoader.java:107) at org.netbeans.modules.netbinox.NetbinoxLoader.loadClass(NetbinoxLoader.java:81) at java.lang.ClassLoader.loadClass(ClassLoader.java:352) ... 10 more |
I thought applying the Open Java FX package might fix the problem. I installed the package like the following:
yum install -y openjfx |
The installation log:
Last metadata expiration check: 4:03:29 ago on Tue 21 Apr 2020 06:42:26 PM MDT. Dependencies resolved. ============================================================================================= Package Architecture Version Repository Size ============================================================================================= Installing: openjfx x86_64 8.0.202-8.b07.fc30 updates 8.8 M Transaction Summary ============================================================================================= Install 1 Package Total download size: 8.8 M Installed size: 11 M Downloading Packages: openjfx-8.0.202-8.b07.fc30.x86_64.rpm 2.5 MB/s | 8.8 MB 00:03 --------------------------------------------------------------------------------------------- Total 2.1 MB/s | 8.8 MB 00:04 Running transaction check Transaction check succeeded. Running transaction test Transaction test succeeded. Running transaction Preparing : 1/1 Installing : openjfx-8.0.202-8.b07.fc30.x86_64 1/1 Running scriptlet: openjfx-8.0.202-8.b07.fc30.x86_64 1/1 Verifying : openjfx-8.0.202-8.b07.fc30.x86_64 1/1 Installed: openjfx-8.0.202-8.b07.fc30.x86_64 Complete! |
After installing the software, I determined the new JAR files. Then, I added them to my $CLASSPATH environment variable, like:
export CLASSPATH=/usr/share/java/mysql-connector-java.jar:/usr/lib/jvm/openjfx/rt/lib/ext/fxrt.jar:/usr/lib/jvm/openjfx/rt/lib/jfxswt.jar:. |
While it appears to load faster with these JAR files, it still raises the same Dialog error. I simply have to continue to look for a complete fix.
Java & MySQL 8.0.19
It’s the in-between term time and we’re all stuck at home. I decided to update the image for my Fedora 30 virtual machine. I had a work around to the update issue that I had encountered last October in Bug #96969 but it was not required with the current version. However, after updating from MySQL 8.0.17 to MySQL 8.0.19, I found that my Java connection example failed.
The $CLASSPATH value was correct:
/usr/share/java/mysql-connector-java.jar:. |
The first error that I got was the my reference to MySQL JDBC driver was incorrect. The error message is quite clear:
Loading class `com.mysql.jdbc.Driver'. This is deprecated. The new driver class is `com.mysql.cj.jdbc.Driver'. The driver is automatically registered via the SPI and manual loading of the driver class is generally unnecessary. Cannot connect to database server: The server time zone value 'MDT' is unrecognized or represents more than one time zone. You must configure either the server or JDBC driver (via the 'serverTimezone' configuration property) to use a more specifc time zone value if you want to utilize time zone support. |
I changed the MySQL Driver reference as instructed by the error message:
29 30 31 | // Create instance of MySQLDriver. Class.forName ("com.mysql.cj.jdbc.Driver").newInstance(); conn = DriverManager.getConnection (url, username, password); |
After the change, I got the following error while retesting my little MySQL Java driver connection test program. Initially, I thought this required a change in the Java environment but that wasn’t it.
Cannot connect to database server: The server time zone value 'MDT' is unrecognized or represents more than one time zone. You must configure either the server or JDBC driver (via the 'serverTimezone' configuration property) to use a more specifc time zone value if you want to utilize time zone support. |
It required me to add the following line to my /etc/my.cnf configuration file, which synchronizes the database’s timezone with the operating system.
# Synchronize the MySQL clock with the computer system clock. default-time-zone='+00:00' |
Then, running my MySQL Driver connection test program worked like a charm. It returns the following:
Database connection established MySQLDriver Version [8.0.19] Database connection terminated |
Here’s the MySQL Connector Java code if you’d like to use the MySQLDriver.java file:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 | // Import classes. import java.sql.*; /* You can't include the following on Linux without raising an exception. */ // import com.mysql.jdbc.Driver; public class MySQLDriver { public MySQLDriver() { /* Declare variables that require explicit assignments because they're addressed in the finally block. */ Connection conn = null; Statement stmt = null; ResultSet rset = null; /* Declare other variables. */ String url; String username = "student"; String password = "student"; String database = "studentdb"; String hostname = "localhost"; String port = "3306"; String sql; /* Attempt a connection. */ try { // Set URL. url = "jdbc:mysql://" + hostname + ":" + port + "/" + database; // Create instance of MySQLDriver. Class.forName ("com.mysql.cj.jdbc.Driver").newInstance(); conn = DriverManager.getConnection (url, username, password); // Query the version of the database. sql = "SELECT version()"; stmt = conn.createStatement(); rset = stmt.executeQuery(sql); System.out.println ("Database connection established"); // Read row returns for one column. while (rset.next()) { System.out.println("MySQLDriver Version [" + rset.getString(1) + "]"); } } catch (SQLException e) { System.err.println ("Cannot connect to database server:"); System.out.println(e.getMessage()); } catch (ClassNotFoundException e) { System.err.println ("Cannot find MySQL driver class:"); System.out.println(e.getMessage()); } catch (InstantiationException e) { System.err.println ("Cannot instantiate class:"); System.out.println(e.getMessage()); } catch (IllegalAccessException e) { System.err.println ("Illegal access exception:"); System.out.println(e.getMessage()); } finally { if (conn != null) { try { rset.close(); stmt.close(); conn.close(); System.out.println ("Database connection terminated"); } catch (Exception e) { /* ignore close errors */ } } } } /* Unit test. */ public static void main(String args[]) { new MySQLDriver(); } } |
As always, I hope this helps those who encounter similar problems.
Java and Postgres
I wanted to get Java working with PostgreSQL to test some GUI interfaces on Linux. Figuring out the necessary JAR file for the JDBC was my first hurdle. I found it was postgreSQL-42-2.5.jar file.
You can download it with the following command line:
wget https://jdbc.postgresql.org/download/postgresql-42.2.5.jar |
I downloaded it to a Java directory off the home/student directory. Then, I added the following CLASSPATH to local java.env environment file.
#!/usr/bin/bash # Set the Java CLASSPATH environment variable to include the JDBC jar file. export set CLASSPATH=/home/student/Java/postgresql-42.2.5.jar:. |
I sourced the postgresql-42.2.5.jar file and I wrote the following JavaTest.java program:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 | /* Import classes. */ import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; import java.util.logging.Level; import java.util.logging.Logger; public class JavaTest { public static void main(String[] args) { /* Set default strings for the connection. */ String url = "jdbc:postgresql://localhost:5432/videodb"; String user = "student"; String password = "student"; /* Try the connection and statement. */ try { Connection conn = DriverManager.getConnection(url, user, password); Statement st = conn.createStatement(); ResultSet rs = st.executeQuery("SELECT VERSION()"); if (rs.next()) { System.out.println(rs.getString(1)); } /* Close the result set and statement. */ rs.close(); st.close(); } catch (SQLException e) { Logger logger = Logger.getLogger(JavaTest.class.getName()); logger.log(Level.SEVERE, e.getMessage(), e); } } } |
I compiled the JavaTest.java program and tested it. It failed with the following error:
FATAL: Ident authentication failed for user - Unable to connect to PostgreSQL |
The failure occurred because I hadn’t allowed the connection in PostgreSQL’s pg_hba.conf file. I changed the following line in my pg_hba.conf file:
host all all 127.0.0.1/32 ident |
to
host all all 127.0.0.1/32 trust |
Then, I restarted the postgresql-11 service, like this:
systemctl restart postgresql-11.service |
The JavaTest program ran successfully and returned:
PostgreSQL 11.5 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 9.1.1 20190503 (Red Hat 9.1.1-1), 64-bit |
You can extend the logic to output a comma-separated value file by leveraging the JDBC help page, like this:
/* Import classes. */ import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.ResultSetMetaData; import java.sql.SQLException; import java.sql.Statement; import java.util.logging.Level; import java.util.logging.Logger; /* Create class withonly a static method for runtime testing. */ public class JavaReturnSet { public static void main(String[] args) { /* Set default strings for the connection. */ String url = "jdbc:postgresql://localhost:5432/videodb"; String user = "student"; String password = "student"; /* Try the connection and statement. */ try { /* Set connection, statement, and result set. */ Connection conn = DriverManager.getConnection(url, user, password); Statement st = conn.createStatement(); /* Use the + to concatenate lines for query clarity. */ ResultSet rs = st.executeQuery("SELECT m.account_number\n" + ", CONCAT(c.last_name,', ',c.first_name)\n" + "FROM member m JOIN contact c\n" + "ON m.member_id = c.member_id"); /* Get query metadata for subsequent management of results. */ ResultSetMetaData rsmd = rs.getMetaData(); String line; while (rs.next()) { /* Initialize the line output for each row. */ line = ""; /* Process the columns. */ for (int i = 0; i < rsmd.getColumnCount(); i++) { if (rsmd.getColumnType(i + 1) == 12) { line = line + "\"" + rs.getString(i + 1) + "\""; } else { line = line + rs.getInt(i + 1); } /* Put a comma between output columns. */ if (i < rsmd.getColumnCount() - 1) { line = line + ","; } } System.out.println(line); } /* Close the result set and statement. */ rs.close(); st.close(); } catch (SQLException e) { Logger logger = Logger.getLogger(JavaReturnSet.class.getName()); logger.log(Level.SEVERE, e.getMessage(), e); } } } |
As always, I hope this helps those looking for a clean solution.
Cassandra on Fedora 30
The first thing to do with Fedora 30 is to check what part of Apache Cassandra is installed. You can use the following rpm command to determine that:
rpm -qa | grep cassandra |
My Fedora 30 returned the following values:
cassandra-java-libs-3.11.1-12.fc30.x86_64 cassandra-python2-cqlshlib-3.11.1-12.fc30.x86_64 cassandra-3.11.1-12.fc30.x86_64 python2-cassandra-driver-3.18.0-1.fc30.x86_64 |
Notably missing from the list of rpm list is the cassandra-server package. You install cassandra-server with the def utility:
dnf install -y cassandra-server |
You should get an installation log like the following for the cassandra-server package:
Display detailed console log →
Last metadata expiration check: 0:26:07 ago on Wed 11 Sep 2019 09:10:08 PM MDT. Package cassandra-3.11.1-12.fc30.x86_64 is already installed. Dependencies resolved. =========================================================================================================================== Package Architecture Version Repository Size =========================================================================================================================== Installing: cassandra-server x86_64 3.11.1-12.fc30 fedora 180 k Installing dependencies: sigar x86_64 1.6.5-0.20.git58097d9.fc27 fedora 76 k Transaction Summary =========================================================================================================================== Install 2 Packages Total download size: 255 k Installed size: 738 k Is this ok [y/N]: y Downloading Packages: (1/2): sigar-1.6.5-0.20.git58097d9.fc27.x86_64.rpm 131 kB/s | 76 kB 00:00 (2/2): cassandra-server-3.11.1-12.fc30.x86_64.rpm 233 kB/s | 180 kB 00:00 --------------------------------------------------------------------------------------------------------------------------- Total 116 kB/s | 255 kB 00:02 Running transaction check Transaction check succeeded. Running transaction test Transaction test succeeded. Running transaction Preparing : 1/1 Installing : sigar-1.6.5-0.20.git58097d9.fc27.x86_64 1/2 Running scriptlet: sigar-1.6.5-0.20.git58097d9.fc27.x86_64 1/2 Running scriptlet: cassandra-server-3.11.1-12.fc30.x86_64 2/2 Installing : cassandra-server-3.11.1-12.fc30.x86_64 2/2 Running scriptlet: cassandra-server-3.11.1-12.fc30.x86_64 2/2 Verifying : cassandra-server-3.11.1-12.fc30.x86_64 1/2 Verifying : sigar-1.6.5-0.20.git58097d9.fc27.x86_64 2/2 Installed: cassandra-server-3.11.1-12.fc30.x86_64 sigar-1.6.5-0.20.git58097d9.fc27.x86_64 Complete! |
Fedora Magazine has a great Get Started with Apache Cassandra on Fedora article on all the steps required to setup clusters. This article only covers creating and enabling the Cassandra service, and setting up a single node Cassandra instance.
You start Cassandra with the following command as the root user:
systemctl start cassandra |
You enable Cassandra with the following command as the root user:
systemctl enable cassandra |
It creates the following symlink:
Created symlink /etc/systemd/system/multi-user.target.wants/cassandra.service → /usr/lib/systemd/system/cassandra.service. |
You can connect to the Test cluster with the following command:
cqlsh |
You should see the following:
Connected to Test Cluster at 127.0.0.1:9042. [cqlsh 5.0.1 | Cassandra 3.11.1 | CQL spec 3.4.4 | Native protocol v4] Use HELP for help. |
You can see the options by typing the help command:
Documented shell commands: =========================== CAPTURE CLS COPY DESCRIBE EXPAND LOGIN SERIAL SOURCE UNICODE CLEAR CONSISTENCY DESC EXIT HELP PAGING SHOW TRACING CQL help topics: ================ AGGREGATES CREATE_KEYSPACE DROP_TRIGGER TEXT ALTER_KEYSPACE CREATE_MATERIALIZED_VIEW DROP_TYPE TIME ALTER_MATERIALIZED_VIEW CREATE_ROLE DROP_USER TIMESTAMP ALTER_TABLE CREATE_TABLE FUNCTIONS TRUNCATE ALTER_TYPE CREATE_TRIGGER GRANT TYPES ALTER_USER CREATE_TYPE INSERT UPDATE APPLY CREATE_USER INSERT_JSON USE ASCII DATE INT UUID BATCH DELETE JSON BEGIN DROP_AGGREGATE KEYWORDS BLOB DROP_COLUMNFAMILY LIST_PERMISSIONS BOOLEAN DROP_FUNCTION LIST_ROLES COUNTER DROP_INDEX LIST_USERS CREATE_AGGREGATE DROP_KEYSPACE PERMISSIONS CREATE_COLUMNFAMILY DROP_MATERIALIZED_VIEW REVOKE CREATE_FUNCTION DROP_ROLE SELECT CREATE_INDEX DROP_TABLE SELECT_JSON |
Here’s my script that creates Cassandra keyspace, which is more or less a database. You use the USE command to connect to the keyspace or database, like you would in MySQL. You do not have sequences in Cassandra because they’re not a good fit for a distributed architecture. Cassandra does not support a native procedural extension like relational databases. You must create User-defined functions (UDFs) by embedding the logic in Java.
This script does the following:
- Creates a keyspace
- Uses the keyspace
- Conditionally drops tables and functions
- Creates two tables
- Inserts data into the two tables
- Queries data from the tables
I also included a call to a UDF inside a query in two of the examples. One of the queries demonstrates how to return a JSON structure from a query. To simplify things and provide clarification of the scripts behaviors, the details are outlined below.
- The first segment of the script creates the keyspace, changes the scope to use the keyspace, conditionally drop tables, create tables, and insert values into the tables:
/* Create a keyspace in Cassandra, which is like a database in MySQL or a schema in Oracle. */ CREATE KEYSPACE IF NOT EXISTS student WITH REPLICATION = { 'class':'SimpleStrategy' ,'replication_factor': 1 } AND DURABLE_WRITES = true; /* Use the keyspace or connect to the database. */ USE student; /* Drop the member table from the student keyspace. */ DROP TABLE IF EXISTS member; /* Create a member table in the student keyspace. */ CREATE TABLE member ( member_number VARCHAR , member_type VARCHAR , credit_card_number VARCHAR , credit_card_type VARCHAR , PRIMARY KEY ( member_number )); /* Conditionally drop the contact table from the student keyspace. */ DROP TABLE IF EXISTS contact; /* Create a contact table in the student keyspace. */ CREATE TABLE contact ( contact_number VARCHAR , contact_type VARCHAR , first_name VARCHAR , middle_name VARCHAR , last_name VARCHAR , member_number VARCHAR , PRIMARY KEY ( contact_number )); /* Insert a row into the member table. */ INSERT INTO member ( member_number, member_type, credit_card_number, credit_card_type ) VALUES ('SFO-12345','GROUP','2222-4444-5555-6666','VISA'); /* Insert a row into the contact table. */ INSERT INTO contact ( contact_number, contact_type, first_name, middle_name, last_name, member_number ) VALUES ('CUS_00001','FAMILY','Barry', NULL,'Allen','SFO-12345'); /* Insert a row into the contact table. */ INSERT INTO contact ( contact_number, contact_type, first_name, middle_name, last_name, member_number ) VALUES ('CUS_00002','FAMILY','Iris', NULL,'West-Allen','SFO-12345'); /* Insert a row into the member table. */ INSERT INTO member ( member_number, member_type, credit_card_number, credit_card_type ) VALUES ('SFO-12346','GROUP','3333-8888-9999-2222','VISA'); /* Insert a row into the contact table. */ INSERT INTO contact ( contact_number, contact_type, first_name, middle_name, last_name, member_number ) VALUES ('CUS_00003','FAMILY','Caitlin','Marie','Snow','SFO-12346');
The following queries the member table:
/* Select all columns from the member table. */ SELECT * FROM member;
It returns the following:
member_number | credit_card_number | credit_card_type | member_type ---------------+---------------------+------------------+------------- SFO-12345 | 2222-4444-5555-6666 | VISA | GROUP SFO-12346 | 3333-8888-9999-2222 | VISA | GROUP
- Create a
concatenateUser-defined function (UDF) for Cassandra. The first step requires you to edit thecassandra.yamlfile, which you find in the/etc/cassandra/default.confdirectory. There is a single parameter that you need to edit, and it is theenable_user_defined_functionsparameter. By default the parameter is set tofalse, and you need to enable it to create UDFs.If you open the
cassandra.yamlfile as therootuser, you should find the parameter on line 987, like:983 984 985 986 987
# If unset, all GC Pauses greater than gc_log_threshold_in_ms will log at # INFO level # UDFs (user defined functions) are disabled by default. # As of Cassandra 3.0 there is a sandbox in place that should prevent execution of evil code. enable_user_defined_functions: false
After you make the edit, the
cassandra.yamlfile should look like this:983 984 985 986 987
# If unset, all GC Pauses greater than gc_log_threshold_in_ms will log at # INFO level # UDFs (user defined functions) are disabled by default. # As of Cassandra 3.0 there is a sandbox in place that should prevent execution of evil code. enable_user_defined_functions: true
After you make the change, you can create your own UDF. The following UDF formats the first, middle, and last name so there’s only one whitespace between the first and last name when there middle name value is null.
This type of function must use a
CALLED ON NULL INPUTclause in lieu of aRETURNS NULL ON NULL INPUTclause. The latter would force the function to return a null value if any one of the parameters were null./* Drop the concatenate function because a replace disallows changing a RETURNS NULL ON NULL INPUT with a CALLED ON NULL INPUT without raising an "89: InvalidRequest" exception. */ DROP FUNCTION concatenate; /* Create a user-defined function to concatenate names. */ CREATE OR REPLACE FUNCTION concatenate (first_name VARCHAR, middle_name VARCHAR, last_name VARCHAR) CALLED ON NULL INPUT RETURNS VARCHAR LANGUAGE java AS $$ /* Concatenate first and last names when middle name is null, and first, middle, and last names when middle name is not null. */ String name; /* Check for null middle name. */ if (middle_name == null) { name = first_name + " " + last_name; } else { name = first_name + " " + middle_name + " " + last_name; } return name; $$;
Query the values from the contact table with the UDF function in the SELECT-list:
/* Query the contact information. */ SELECT member_number , contact_number , contact_type , concatenate(first_name, middle_name, last_name) AS full_name FROM contact; |
It returns the following:
member_number | contact_number | contact_type | full_name ---------------+----------------+--------------+-------------------- SFO-12345 | CUS_00001 | FAMILY | Barry Allen SFO-12345 | CUS_00002 | FAMILY | Iris West-Allen SFO-12346 | CUS_00003 | FAMILY | Caitlin Marie Snow |
Query the values from the contact table with a JSON format:
/* Query the contact information and return in a JSON format. */ SELECT JSON contact_number , contact_type , concatenate(first_name, middle_name, last_name) AS full_name FROM contact; |
It returns the following:
[json] ------------------------------------------------------------------------------------------------- {"contact_number": "CUS_00001", "contact_type": "FAMILY", "full_name": "Barry Allen"} {"contact_number": "CUS_00002", "contact_type": "FAMILY", "full_name": "Iris West-Allen"} {"contact_number": "CUS_00003", "contact_type": "FAMILY", "full_name": "Caitlin Marie Snow"} |
Subscribe via RSS