Java/es

This guide introduces the reader to Java and explains how to use Java with Gentoo Linux.

Visión general
Java es un lenguaje de programación desarrollado por ingenieros de Sun Microsystems. El lenguaje es totalmente orientado a objetos y diseñado para ser ejecutado en múltiples plataformas sin la necesidad de recompilar el código para cada una de ellas. Aunque Java puede ser compilado como un lenguaje nativo, mucha de la popularidad de Java se atribuye a su portabilidad, junto con otras características como recolección de basura. Para hacer posible esta independencia de plataforma, el compilador de Java compila el codigo Java hacia una representación intermedia denominada "Java bytecode" que es ejecutado en un JRE (Java Runtime Environment) y no directamente sobre el sistema operativo.

Para ejecutar Java bytecode, es necesario tener un entorno JRE (Java Runtime Environment) instalado. Un JRE proporciona bibliotecas centrales, una maquina virtual de Java dependiente de plataforma, y extensiones para navegadores web entre otras cosas. Por otro lado un JDK (Java Development Kit) agrega herramientas de programación, tales como compilador de bytecode y un depurador de codigo.

Opciones
Gentoo proporciona una variedad de entornos de ejecución de Java (JREs) y kits de desarrollo Java (JDKs). Las opciones actuales incluyen:

Instalar un JRE/JDK
To install the profile's default JDK run:

Para instalar el perfil JRE por defecto lanzar:

Some JDKs and JREs, including the Oracle packages, require accepting an End User License Agreement, or EULA. If its license (such as dlj-1.1) is not listed in the ACCEPT_LICENSE variable (found in ), then the JDK/JRE will be unable to be installed. For more information on how to add acceptable licenses to read the Licenses chapter of the Portage Handbook.

Para evitar cualquier restricción de licencias, considérese instalar icedtea-bin, el cual es una implementación abierta de Java del proyecto OpenJDK.

Instalando maquinas virtuales con descarga restringida
Algunos JDKs y JREs necesitan unos pasos adicionales para realizar sus configuraciones. Hacer emerge de los paquetes tal y como se realiza normalmente. Si son necesarios pasos adicionales, los ebuilds ofrecerán instrucciones para los usuarios acerca de dónde ir y qué descargar.

Download the indicated file(s) into Once the files are in the right directories, rerun the  command, at which point the JRE/JDK will be begin to install.

Configurar un JRE sin monitor ni teclado
Sometimes there is no need for a full JRE with all the capabilities of java. Using java on a server often does not require any GUI, graphical, sound or even printer related features. To install a simplified (sometimes also referred to as headless) JRE, a few USE flags need to be changed.

Depending on the current Gentoo profile, this might already be the case. As usual, the USE flag settings that are applicable to a particular package can be checked by running in pretend mode:

Visión general
Gentoo posee la habilidad de instalar multiples JDKs y JREs sin causar conflictos.

Using the tool with root privileges, a system-wide default java virtual machine (VM) can be set. Users can also use java-config to custom set their personal VM on a user-by-user basis.

Estableciendo una maquina virtual por defecto
Running the command with the   option will output a list of all JREs and JDKs installed on the system. Here is an example of the output:

The * indicates this is the current active JVM (system-vm or user-vm when set). The name in the brackets ([]) is the handle or ID for that particular VM. The handle or the number to can be used to set the VM. The following text provides an example of how to set the system VM.

Estableciendo la maquina virtual manualmente (modo preferido):

Método alternativo: seleccionar la máquina virtual por número:

Como usuario normal, utilizar java-config.

Build only VM
Some virtual machines are flagged as build-only due to being EOL and/or containing security vulnerabilities. These virtual machines will not automatically be used by Gentoo for the running of applications using Gentoo launchers (run-java-tool script designed for switching VMs), but will still be available for use by Gentoo's build environment as some packages may require them for building. The setting of these virtual machines as either the system or user VM is strongly discouraged as these VMs will then be used when running the executables, as well as used by any packages not using Gentoo's launcher scripts.

Estableciendo un CLASSPATH por defecto
can also be used to set a system-wide default CLASSPATH, as well a user-specific default CLASSPATH.

First, list available Java libraries installed on the system to possibly put in the CLASSPATH variable. Here is an example of output:

Again, the names in brackets ([]) are the IDs to pass to. Here is an example:

Update the environment by logging out, then in again or by typing

For users, java-config --set-user-classpath will create, which should then source from the shell's profile.

If desiring a system wide or user default classpath add something like the following to the shell's profile. This is advised against:

Java browser plugins
The Java browser plugin used to be managed via. This has now been removed in favor of a simpler out-of-the-box experience. For basic usage, simply emerge the chosen JVM with the  USE flag enabled. Note that Oracle's plugin is only available for and.

Also note that Chromium-based browsers no longer support NPAPI-based plugins since the code was removed in September 2015. The list of supporting browsers is shrinking but still includes Firefox as of version 46.

For more information, including JVM selection, Web Start, and multilib, see the README installed with icedtea-web.

Establecer los ajustes USE
For more information regarding USE flags, refer to the USE flags chapter from the Gentoo Handbook.

USE flags

 * The flag adds support for Java in a variety of programs;
 * The flag adds support for Mozilla-like browsers (including Firefox). This is needed for viewing Java applets in a Mozilla-like browser;
 * The flag adds support for the Java Cryptography Engine;

Following USE flags go in JAVA_PKG_IUSE.
 * The flag installs a zip of the source code of a package. This is traditionally used for IDEs to 'attach' source to the libraries that are being use;
 * For Java packages, the flag will build API documentation using javadoc.

Ver también

 * The Java User Guide in the Java project

Recursos externos

 * The gentoo-java, gentoo-user, and gentoo-dev mailing list archives
 * and on IRC
 * Java 7 and bootstrapping icedtea on the Gentoo forums

More information can be found offline:



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