I have a Macbook Pro running El Capitan (10.11.6). It doesn't come with Java and the advise I heard is to not install it because it's unsafe (and apparently Oracle bundles the installation with some ask bar tool or adware so I don't want that).
However, is there a way to code in Java without that? When I try to run Java programs from terminal (java foo.java), it tells me I need it. Is it just the browser plugin that's unsafe or should I keep it away from my computer entirely?
You can't, Java programs run in a virtual machine that you need to install (by installing the Java Runtime Environment).
You shouldn't run into any risks just by installing Java in and of itself, as long as you run programs that you know you can trust. If you really want to feel safe, disable the Java plugin from your browser (Actually, I checked and my broswer doesn't have any Java plugin installed, so you don't even need to do that). The toolbar is completely optional, just uncheck the option during installation.
If you want to write Java code you'll have to install the Java SDK too.
I started to develop a simple application with express.js and node.jdbc. This node-jdbc uses node java and this depends on the installed JDK on my machine.
To make my little try independent from the environment I want to use a portable JRE within my bundle.
So is there a possibility to include and use a portable JRE for the node-jdbc?
And how can it be done?
I have a very old application (published in 2001) I am trying to get working in Windows 7/8/10. There is a setup.exe part of it that is using Java in some capacity, and not working correctly. I suspect it is using java because I decompiled the JAR file packaged with the application and there are references to several setup steps within the .java files (along with a file named setup.java). There is also a jre folder published with the application as well, running the following (dated) version:
F:\jre\bin>java -version
java version "1.3.0_01"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.0_01)
Java HotSpot(TM) Client VM (build 1.3.0_01, mixed mode)
At first I suspected the application was using the systems environmental variables to use the currently installed version of JAVA, but I ruled that out by completely purging JAVA from the system and retesting - same results.
I next tried to simply update the folder to the latest version. As expected however, there were calls being made that were no longer supported (error message was referencing _JVM_IsVMGeneratedMethodl).
At this point I am running out of options. I could always run this application in a VM (and it works fine), but I would prefer to somehow package it in a nice streamlined way for easy distribution and install. Is there anything I can do? I was thinking something along the lines of application virtualization but still reading up on it.
It's hard to tell without "being there", but I'm guessing that the old (1.3) JVM just isn't compatible with the more modern versions of Windows.
Your best bet is probably running it against whatever version of Windows the app was originally developed on, in a VM.
If you have / can get the complete source code, you could try recompiling it with the version of Java supported on your current system. But it's probably a long-shot.
If it is containing a JRE folder, then you could skip the installer and add some batch file to launch that .jar with the specific JRE via a command of this form:
java -jar pathToYourJAR
btw, you could also consider options to convert to executable, some older are mentioned here:
How can I convert my Java program to an .exe file?
some of them may allow you to select which JRE to bundle/use
Could anyone please tell how jre directory help in the running java programs? I'm calling java interpretor by using java command, and that is in JDK directory, then how could jre directory help in running java programs and jdk for compiling?
When you install the JDK (development kit, compiler and so on), you get the JRE (runtime environment) as part of that (under my install, there's actually a jre subdirectory in the jdk folder) - this is because you will probably want to run code that you develop if only to test it a little bit before inflicting it on the rest of the planet :-).
But it's by no means necessary to install the JDK to run Java programs. All you need is the JRE and that is, by far, the normal situation for most people out there.
The JRE is just the interpreter (java.exe or whatever) - it's a smaller install that is typically used by people who just need to run Java applications and aren't Java developers. The JRE handles the conversion and execution of java bytecode for the target platform.
The JDK is meant for developers. Along with the runtime it provides the compiler and all the Java libraries that are used to build Java programs. The compiler is responsible for converting Java source code to bytecode.
So - when you are delivering your Java application to customers, all they need to install is the JRE.
The Java Runtime Environment (JRE) interprets byte code to platform specific machine code. JRE is minimal set of programmes which executes the java class files.
The JDK (Java Developmental Toolkit) comes along with java libraries and JRE embedded in it. Apart from these it comes along with the utility tools for byte code compilation "javac".
We have a couple of applications running on Java 5 and would like now to bring in an application based on Java 6. Can both java versions live together under Windows?
Is there any control panel to set the appropriate Java version for different applications, or any other way to set up, what version of Java will be used to run that particular application?
Of course you can use multiple versions of Java under Windows. And different applications can use different Java versions. How is your application started? Usually you will have a batch file where there is something like
java ...
This will search the Java executable using the PATH variable. So if Java 5 is first on the PATH, you will have problems running a Java 6 application. You should then modify the batch file to use a certain Java version e.g. by defining a environment variable JAVA6HOME with the value C:\java\java6 (if Java 6 is installed in this directory) and change the batch file calling
%JAVA6HOME%\bin\java ...
I was appalled at the clumsiness of the CLASSPATH, JAVA_HOME, and PATH ideas, in Windows, to keep track of Java files. I got here, because of multiple JREs, and how to content with it. Without regurgitating information, from a guy much more clever than me, I would rather point to to his article on this issue, which for me, resolves it perfectly.
Article by: Ted Neward: Multiple Java Homes: Giving Java Apps Their Own JRE
With the exponential growth of Java as a server-side development language has come an equivablent
exponential growth in Java development tools, environments, frameworks, and extensions.
Unfortunately, not all of these tools play nicely together under the same Java VM installation. Some
require a Servlet 2.1-compliant environment, some require 2.2. Some only run under JDK 1.2 or above,
some under JDK 1.1 (and no higher). Some require the "com.sun.swing" packages from pre-Swing 1.0
days, others require the "javax.swing" package names.
Worse yet, this problem can be found even within the corporate enterprise, as systems developed using
Java from just six months ago may suddenly "not work" due to the installation of some Java Extension
required by a new (seemingly unrelated) application release. This can complicate deployment of Java
applications across the corporation, and lead customers to wonder precisely why, five years after the
start of the infamous "Installing-this-app-breaks-my-system" woes began with Microsoft's DLL schemes,
we still haven't progressed much beyond that. (In fact, the new .NET initiative actually seeks to solve the
infamous "DLL-Hell" problem just described.)
This paper describes how to configure a Java installation such that a given application receives its own,
private, JRE, allowing multiple Java environments to coexist without driving customers (or system
administrators) insane...
It is absolutely possible to install side-by-side several JRE/JDK versions. Moreover, you don't have to do anything special for that to happen, as Sun is creating a different folder for each (under Program Files).
There is no control panel to check which JRE works for each application. Basically, the JRE that will work would be the first in your PATH environment variable. You can change that, or the JAVA_HOME variable, or create specific cmd/bat files to launch the applications you desire, each with a different JRE in path.
We can install multiple versions of Java Development kits on the same machine using SDKMan.
Some points about SDKMan are as following:
SDKMan is free to use and it is developed by the open source community.
SDKMan is written in bash and it only requires curl and zip/unzip programs to be present on your system.
SDKMan can install around 29 Software Development Kits for the JVM such as Java, Groovy, Scala, Kotlin and Ceylon. Ant, Gradle, Grails, Maven, SBT, Spark, Spring Boot, Vert.x.
We do not need to worry about setting the _HOME and PATH environment variables because SDKMan handles it automatically.
SDKMan can run on any UNIX based platforms such as Mac OSX, Linux, Cygwin, Solaris and FreeBSD and we can install it using following commands:
$ curl -s "https://get.sdkman.io" | bash
$ source "$HOME/.sdkman/bin/sdkman-init.sh"
Because SDKMan is written in bash and only requires curl and zip/unzip to be present on your system. You can install SDKMan on windows as well either by first installing Cygwin or Git Bash for Windows environment and then running above commands.
Command sdk list java will give us a list of java versions which we can install using SDKMan.
Installing Java 8
$ sdk install java 8.0.201-oracle
Installing Java 9
$ sdk install java 9.0.4-open
Installing Java 11
$ sdk install java 11.0.2-open
Uninstalling a Java version
In case you want to uninstall any JDK version e.g., 11.0.2-open you can do that as follows:
$ sdk uninstall java 11.0.2-open
Switching current Java version
If you want to activate one version of JDK for all terminals and applications, you can use the command
sdk default java <your-java_version>
Above commands will also update the PATH and JAVA_HOME variables automatically. You can read more on my article How to Install Multiple Versions of Java on the Same Machine.
It should be possible changing setting the JAVA_HOME environment variable differently for specific applications.
When starting from the command line or from a batch script you can use set JAVA_HOME=C:\...\j2dskXXX to change the JAVA_HOME environment.
It is possible that you also need to change the PATH environment variable to use the correct java binary. To do this you can use set PATH=%JAVA_HOME%\bin;%PATH%.
I use a simple script when starting JMeter with my own java version
setlocal
set JAVA_HOME="c:\java8"
set PATH=%JAVA_HOME%\bin;%PATH%;
java -version
To have a java "portable"
you can use this method here:
https://www.whitebyte.info/programming/java/how-to-install-a-portable-jdk-in-windows-without-admin-rights
Or use links. While it is rather unpleasant to update the PATH in a running environment, it's easy to recreate a link to a new version of JRE/JDK. So:
install different versions of JDK you want to use
create a link to that folder either by junction or by built-in mklink command
set the PATH to the link
If other version of java is to be used, delete the link, create a new one, PATH/JAVA_HOME/hardcoded scripts remain untouched
Invoking Java with "java -version:1.5", etc. should run with the correct version of Java. (Obviously replace 1.5 with the version you want.)
If Java is properly installed on Windows there are paths to the vm for each version stored in the registry which it uses so you don't need to mess about with environment versions on Windows.
If you use Java Web Start (you can start applications from any URL, even the local file system) it will take care of finding the right version for your application.
Using Java Web Start, you can install multiple JRE, then call what you need.
On win, you can make a .bat file:
1- online version:
<your_JRE_version\bin\javaws.exe> -localfile -J-Djnlp.application.href=<the url of .jnlp file.jnlp> -localfile -J "<path_temp_jnlp_file_.jnlp>"
2- launch from cache:
<your_JRE_version\bin\javaws.exe> -localfile -J "<path_of_your_local_jnlp_file.jnlp>"