In late April 2021 I had to install a Java development environment in my Ubuntu 20.04 machine and be able to use my Ant/Ivy-based build machinery with local IVY repositories. What follows is a writeup of how I proceeded.

The Java 11 runtime was already installed so I only needed to install the JDK with:

sudo apt install javac

It should be noted that in the previous Java developement environment I had on the T460 ThinkPad machine I had Java 8. This caused a problem further down the road (read on).

I then installed Ant with:

sudo apt install ant

The next question was how to install Ivy. Here, I tried various approaches and even though some initial ones were successful, in the end I used a different method. As documented, Ivy is simply a jar and it can be installed in two ways:

1. locally, for the current user, at ~/.ant/lib
2. in some global location which you can google

Furthermore, in Ubuntu 20 there's also a third way:

3. by using

   sudo apt install ivy

   which places the ivy.jar under /usr/share/java

Next, I had to install some auxiallary Ant tasks (ant-contrib) which is some sort of abandonware available at: sourceforge. This project only makes the sources available (not the compiled library) and I had some issues getting the code to compile. Fortunately, once I copied over the /proj/DS.ots directory as mentioned above, this point too became moot as the ant-contrib library is available there too, as well, as an OTS dependency.

I then had to edit the various build.xml scripts as in the T460 laptop they used absolute paths to reach the home of the archetype-java-ant-ivy/build-system-machinery whereas in the P320 desktop I am using relative paths. In the same spirit, I also had to change certain symlinks to use relative, instead of absolute, paths (the latter never being a good idea).

In the save vein I had to change some hardcoded executables, e.g. the javac.executable property in file /repos/prj/archetype-java-ant-ivy/build-system-machinery/build-env.properties

Finally, another issue I had to solve was that in Java 11 the javax.activation package is not available (it has actually been retired since Java 9). As such I was getting a compilation error in the ~/repos/prj/js-react-leaflet/common project. The solution was found in SO. To implement the SO solution I had to add the following ivy dependency in the ivy,xml file of the above-mentioned project.

<dependency org="com.sun.activation" name="javax.activation" rev="1.2.0" conf="compile-time->master"/> 

<property name="enable-ibiblio" value="true"/>

After the above modifications, I was able to fully build the js-react-leaflet project. However, I also wanted to recreate the entire LFSBIR from scratch as opposed to copying it over from the ThinkPad T460 machine and also include this new dependency there (in the LFSBIR) as opposed to setting the enable-ibiblio property to true. To that end I modified file ~/repos/prj/archetype-java-ant-ivy/ivy-importation-to-local-fs/build-ivy-install-local.xml and discoverd, in the process, that I had to further retrieve a couple of more additional packages there. During this process I also changed the properties in the /data/asc3/mperdike/ directory to make it writable. I was then able to fetch a fresh /data/asc3/mperdike/local-ivy-repository and I verified that its size profile was similar to the previous one.

I then removed the enable-ibiblio property from the build.xml file in the ~/repos/prj/js-react-leaflet/common project , cleaned the Ivy cache, re-build everything (including the sibling rest-backend project and so successfully concluded this process.

update June 25 2021

When trying to implement the new Java-based IACS backend I ended up adding:
<dependency org="javax.activation" name="activation" rev="1.1" conf="compile-time->master"/>
… which also worked. Initially I had tried to use rev="1.1.1" (from some other SO answer I won't bother linking to) but that failed as that exact version was not present in the LFSBIR.

The following worked like a charm in June, 2019

$ sudo apt-get install openjdk-8-jdk
$ sudo apt-get install openjdk-8-jre
$ sudo update-alternatives --config java
$ sudo update-alternatives --config javac

With hindsight it was probably uncessary to install the JRE once I had already installed the JDK but then again it didn't hurt either.

NB: even after updating the alternatives, the JAVA_HOME environment in my shell was:

 $ echo $JAVA_HOME
/usr/lib/jvm/java-8-oracle

$ cat /etc/profile.d/jdk.sh
export J2SDKDIR=/usr/lib/jvm/java-8-oracle
export J2REDIR=/usr/lib/jvm/java-8-oracle/jre
export PATH=$PATH:/usr/lib/jvm/java-8-oracle/bin:/usr/lib/jvm/java-8-oracle/db/bin:/usr/lib/jvm/java-8-oracle/jre/bin
export JAVA_HOME=/usr/lib/jvm/java-8-oracle
export DERBY_HOME=/usr/lib/jvm/java-8-oracle/db

Java JAR files may be compared with the awesome package change analyzer pkgdiff — which in fact can be used to visualize changes in any kind of Linux software package.

$ pkgdiff dist/cxcaccount-1.0.0.war dist.safe/cxcaccount-1.0.0.war
reading packages ...
comparing packages ...
creating changes report ...
result: CHANGED (0.01%)
see detailed report:
  pkgdiff_reports/cxcaccount/1.0.0_to_1.0.0/changes_report.html
$ echo $?
1

While compiling (using Ant) on a machine with 12 cores I encountered the following failure while running ant build:

    [javac] # There is insufficient memory for the Java Runtime Environment to continue.
    [javac] # Cannot create GC thread. Out of system resources.
    [javac] # An error report file with more information is saved as:
    [javac] # /tmp/jvm-21655/hs_error.log

Following the advice given in this SO answer I did:

export _JAVA_OPTIONS="-XX:ParallelGCThreads=2"

That fixed it. Apparently the JVM was creating too many garbage collection threads (because of the high number of cores) and that caused the memory exhaustion.

On August 2016 I followed the following procedure (source mutatis mutandis) to install Oracle Java 1.7 after I had downloaded from the Oracle site file jdk-7u80-linux-x64.tar.gz

NB: I have copied the below instructions from the article linked above and I haven't replaced all filenames and version names, but the procedure should be obvious.

1. Download the 32-bit or 64-bit Linux from "http://www.oracle.com/technetwork/java/javase/downloads/index.html" "compressed binary file" - it has a ".tar.gz" file extension.
2. Uncompress it:

   tar xvfz jdk-7u80-linux-x64.tar.gz
   

   … the JDK 7 package is extracted into ./jdk1.7.0_75 directory.
3. Now move the JDK 7 directory to /usr/lib

   sudo mkdir -p /usr/lib/jvm
   sudo mv ./jdk1.7.0_75 /usr/lib/jvm/
   

4. Now run

   sudo update-alternatives --install "/usr/bin/java" "java" "/usr/lib/jvm/jdk1.7.0_75/bin/java" 1
   sudo update-alternatives --install "/usr/bin/javac" "javac" "/usr/lib/jvm/jdk1.7.0_75/bin/javac" 1
   sudo update-alternatives --install "/usr/bin/javaws" "javaws" "/usr/lib/jvm/jdk1.7.0_75/bin/javaws" 1
   

   This will assign Oracle JDK a priority of 1, which means that installing other JDKs will replace it as the default. Be sure to use a higher priority if you want Oracle JDK to remain the default.
5. Correct the file ownership and the permissions of the executables:

   sudo chmod a+x /usr/bin/java
   sudo chmod a+x /usr/bin/javac
   sudo chmod a+x /usr/bin/javaws
   sudo chown -R root:root /usr/lib/jvm/jdk1.7.0_75
   

6. Run

   sudo update-alternatives --config java
   

   You will see output similar to the one below - choose the number of jdk1.7.0_75 - for example 3 in this list (unless you have have never installed Java installed in your computer in which case a sentence saying "There is nothing to configure" will appear):

   $ sudo update-alternatives --config java
   There are 3 choices for the alternative java (providing /usr/bin/java).
   
     Selection    Path                                  Priority   Status
   ------------------------------------------------------------
   * 0            /usr/lib/jvm/java-6-oracle1/bin/java   1047      auto mode
     1            /usr/bin/gij-4.6                       1046      manual mode
     2            /usr/lib/jvm/java-6-oracle1/bin/java   1047      manual mode
     3            /usr/lib/jvm/jdk1.7.0_75/bin/java      1         manual mode
   
   Press enter to keep the current choice[*], or type selection number: 3
   update-alternatives: using /usr/lib/jvm/jdk1.7.0_75/bin/java to provide /usr/bin/java (java) in manual mode
   

   Repeat the above for:

   sudo update-alternatives --config javac
   sudo update-alternatives --config javaws
   

jinfo

$ sudo jinfo 1752 | grep arch.data.model
Attaching to process ID 1752, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 24.80-b11
sun.arch.data.model = 32

• if you are inside Java

System.getProperty("sun.arch.data.model")

• outside Java

java -d64 -version

(will display a message if the version is not 64-bit)

java -d32 -version

(will display a message if the version is not 32-bit)

netstat -a | grep TIME_WAIT | wc -l

$ cat /proc/sys/net/ipv4/ip_local_port_range 
3276861000

• increase the range of ephemeral ports
• configure the OS to reuse/recycle sockets in TIME_WAIT state

echo "1" >/proc/sys/net/ipv4/tcp_tw_reuse
echo "1" >/proc/sys/net/ipv4/tcp_tw_recycle

• change the OS configuration that governs for how many seconds a socket will remain in this state - typically a few hundrend (?)
• change the application logic to reduce the need to rapidly open and close a large number of sockets or DB connections

Exception in thread "main" _int.esa.esavo.common.ShowStopper: org.postgresql.util.PSQLException: The connection attempt failed.
          at _int.esa.esavo.dbbusiness.Statistics.repoNameFromIvoid(Statistics.java:216)
          at _int.esa.esavo.dbbusiness.RepoNameFromIvoidTransformer.transform(RepoNameFromIvoidTransformer.java:54)
          at _int.esa.esavo.dbbusiness.RepoNameFromIvoidTransformer.transform(RepoNameFromIvoidTransformer.java:18)
          at _int.esa.esavo.consoleutils.valgraph.VALGRAPHStatsPlot.transform2(VALGRAPHStatsPlot.java:419)
          at _int.esa.esavo.consoleutils.valgraph.VALGRAPHStatsPlot.produce(VALGRAPHStatsPlot.java:255)
          at _int.esa.esavo.consoleutils.valgraph.VALGRAPHStatsPlot.produce(VALGRAPHStatsPlot.java:180)
          at _int.esa.esavo.consoleutils.esaknife.MonthlyReports.produceStatisticsByResource(MonthlyReports.java:234)
          at _int.esa.esavo.consoleutils.esaknife.MonthlyReports.produceStatistics(MonthlyReports.java:194)
          at _int.esa.esavo.consoleutils.esaknife.MonthlyReports.produceReports(MonthlyReports.java:184)
          at _int.esa.esavo.consoleutils.esaknife.MonthlyReports.produce(MonthlyReports.java:136)
          at _int.esa.esavo.consoleutils.esaknife.EsavoSwissKnife.main(EsavoSwissKnife.java:78)
Caused by: org.postgresql.util.PSQLException: The connection attempt failed.
       at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:150)
       at org.postgresql.core.ConnectionFactory.openConnection(ConnectionFactory.java:66)
       at org.postgresql.jdbc2.AbstractJdbc2Connection.(AbstractJdbc2Connection.java:125)
       at org.postgresql.jdbc3.AbstractJdbc3Connection.(AbstractJdbc3Connection.java:30)
       at org.postgresql.jdbc3g.AbstractJdbc3gConnection.(AbstractJdbc3gConnection.java:22)
       at org.postgresql.jdbc4.AbstractJdbc4Connection.(AbstractJdbc4Connection.java:30)
       at org.postgresql.jdbc4.Jdbc4Connection.(Jdbc4Connection.java:24)
       at org.postgresql.Driver.makeConnection(Driver.java:393)
       at org.postgresql.Driver.connect(Driver.java:267)
       at org.apache.commons.dbcp.DriverConnectionFactory.createConnection(DriverConnectionFactory.java:38)
       at org.apache.commons.dbcp.PoolableConnectionFactory.makeObject(PoolableConnectionFactory.java:582)
       at org.apache.commons.pool.impl.GenericObjectPool.borrowObject(GenericObjectPool.java:1148)
       at org.apache.commons.dbcp.PoolingDataSource.getConnection(PoolingDataSource.java:106)
       at org.apache.commons.dbcp.BasicDataSource.getConnection(BasicDataSource.java:1044)
       at _int.esa.esavo.dbbusiness.BaseDBFacade.getConnection(BaseDBFacade.java:16)
       at _int.esa.esavo.dbbusiness.Statistics.repoNameFromIvoid(Statistics.java:172)
       ... 10 more
Caused by: java.net.NoRouteToHostException: Cannot assign requested address
       at java.net.PlainSocketImpl.socketConnect(Native Method)
       at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339)
       at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200)
       at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
       at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
       at java.net.Socket.connect(Socket.java:579)
       at java.net.Socket.connect(Socket.java:528)
       at java.net.Socket.(Socket.java:425)
       at java.net.Socket.(Socket.java:208)
       at org.postgresql.core.PGStream.(PGStream.java:62)
       at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:76)
       ... 25 more

<project
    xmlns:ivy="antlib:org.apache.ivy.ant"
    name="test" default="test-ivy">
<target name="test-ivy">
    <ivy:settings />
</target>
</pre>
</project>

$ whoami
voops
$ ant
Buildfile: build.xml

test-ivy:

BUILD FAILED
/home/voops/test/build.xml:7: Problem: failed to create task or type antlib:org.apache.ivy.ant:settings
Cause: The name is undefined.
Action: Check the spelling.
Action: Check that any custom tasks/types have been declared.
Action: Check that any / declarations have taken place.
No types or tasks have been defined in this namespace yet

This appears to be an antlib declaration. 
Action: Check that the implementing library exists in one of:
        -/usr/share/ant/lib
        -/home/voops/.ant/lib
        -a directory added on the command line with the -lib argument


Total time: 0 seconds

    <taskdef uri="antlib:org.apache.ivy.ant" resource="org/apache/ivy/ant/antlib.xml" classpath="${user.home}/.ant/lib/ivy-2.3.0.jar"/>

<project
    xmlns:ivy="antlib:org.apache.ivy.ant"
    name="test" default="test-ivy">
    <taskdef uri="antlib:org.apache.ivy.ant" resource="org/apache/ivy/ant/antlib.xml" classpath="${user.home}/.ant/lib/ivy-2.3.0.jar"/>
<target name="test-ivy">
    <ivy:settings />
</target>
</pre>
</project>

#!/usr/bin/env bash
EXPR=/usr/bin/expr
/bin/false
START=$(/bin/date +%s)
RESULT=0
COUNTER=0
while IFS= read -r -u3 -d $'\0' file; do
        echo -n "building $file ..."
        ant -f "$file" build > "$file.log" 2>&1 &&
           echo "success" ||
           { echo "failure" && cat "$file.log" ; RESULT=1 ; break; }
        COUNTER=$((COUNTER + 1))
done 3< <(find a b c d -iname build.xml -print0)

END=$(/bin/date +%s)
DIFF=$($EXPR $END - $START)

if [ $RESULT -eq 0 ]
then
    echo "! build successfully concluded for all $COUNTER projects in $DIFF seconds"
else
    echo "X build failed after $COUNTER projects"
fi

jstack -l 30600

• jvisualvm - ships with Oracle JDK 7
• jconsole

jps

jps -p

java -d64 -version

1. I've created script ant_mod in ~/tools which echoes the java executable used to spawn ant
2. use: ant -verbose
3. use: ant -diagnostics | grep java.vm

sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java7-installer

• The SAX API is a widely accepted and well-working parser that is easy to implement and works especially well with streaming content (e.g. an online XML source). Because it is a read-only API, you would not be able to modify the underlying XML data source. Since it only reads one node at a time, it is very memory-efficient and fast. However, this implies that your application expects the information to be close together and ordered.
• If you want to randomly access the entire document at any point of time, then the DOM approach might be a better choice for you. The DOM API is more complex and harder to implement, but gives you full control over the whole document and lets you modify the data, also. However, it reads the whole XML document into memory, so the DOM API is not suitable for projects with very large XML files.

1. download and explode the ivy tarball (apache-ivy-2.2.0-bin.tar.gz)
2. copy the file ivy-2.2.0.jar to where the Ant libs are kept:

sudo cp ivy-2.2.0.jar /usr/share/ant/lib/

3. run the install target in an Ant project of mine:

cd ~/esavo-reg/playground/ivy/02-install
ant install
            

4. you're good to go!

sudo apt-get install ivy

sudo ln -s -T /usr/share/java/ivy.jar /usr/share/ant/lib/ivy.jar

1. download the JDK tar.gz and extract it
2. create a new folder:

sudo mkdir -p /usr/lib/jvm/jdk1.7.0

3. move the extracted contents of the JDK to the new location:

sudo mv /* /usr/lib/jvm/jdk1.7.0/

4. run the following commands one by one:

     sudo update-alternatives --install "/usr/bin/java" "java" "/usr/lib/jvm/jdk1.7.0/bin/java" 1
     sudo update-alternatives --install "/usr/bin/javac" "javac" "/usr/lib/jvm/jdk1.7.0/bin/javac" 1 
     sudo update-alternatives --install "/usr/bin/javap" "javap" "/usr/lib/jvm/jdk1.7.0/bin/javap" 1
     sudo update-alternatives --install "/usr/bin/javaws" "javaws" "/usr/lib/jvm/jdk1.7.0/bin/javaws" 1
     sudo update-alternatives --install "/usr/bin/jar" "jar" "/usr/lib/jvm/jdk1.7.0/bin/jar" 1
     sudo update-alternatives --install "/usr/bin/wsimport" "wsimport" "/usr/lib/jvm/jdk1.7.0/bin/wsimport" 1
     sudo update-alternatives --install "/usr/bin/xjc" "xjc" "/usr/lib/jvm/jdk1.7.0/bin/xjc" 1
    

2013-06-05 update:

jvisualvm --openpid $(ps aux | grep java | grep tandal | awk '{print $2}'

String serverConfUrl = System.getProperty("jboss.server.config.dir") ;

javac -encoding utf-8 X.java // or utf8, UTF-8, UTF8
java -Dfile.encoding=UTF8 X

public class X {
    public static void main (String args[]) {
        System.out.println("\u0222");
    }
}

ANT_OPTS
-Dfile.encoding=UTF8

JAVA_TOOL_OPTIONS
-Dfile.encoding=UTF8

echo repo-wide-libs/*jar | sed 's, ,:,g'

java -cp $(echo lib/*.jar | tr ' ' ':') ..

<compilerarg line="-encoding utf-8"/>

On some occassions I've also used:

<compilerarg line="-encoding ISO-8859-1"/>

sudo add-apt-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java7-installer

java -version

java version "1.7.0_04"
Java(TM) SE Runtime Environment (build 1.7.0_04-b20)
Java HotSpot(TM) Server VM (build 23.0-b21, mixed mode)