Ubuntu: OpenJDK 8 - Unable to locate package

问题:

So I just installed Ubuntu, and this is my first time working in a Linux environment, so bear with my noobishness here.

Anyway, I downloaded the Java 8 JDK directly from Oracle, but I understand there's also an OpenJDK for Java 8 as well. I have two questions.

1. What is the difference between the Oracle version and OpenJDK. Pros/Cons?

2. When I try and get OpenJDK 8, I can't. I'm pasting the terminal command and the error message I get here, hoping for advice. Again, very new to Linux, been on my first Linux distro ever for less than an hour here at this point.

   user@computer:~/Java$ sudo apt-get install openjdk-8-jdk Reading package lists... Done Building dependency tree        Reading state information... Done E: Unable to locate package openjdk-8-jdk 

Any help would be appreciated. In the meantime, I'm just gonna use the Oracle package. Thanks.

Edit:

So, now I have a new problem. I installed OpenJDK 7, it came with Maven and just installed before I realized I was getting a two-for-one deal. Now I have JDK 7, and Eclipse, and Maven, and they're all working, but I'm stuck on JDK 7 rather than 8.

I saw that there's a link below, I intend to check it out in the morning, it's 2am and I'm tired right now. Any other advice for this new issue would be appreciated, otherwise I will definitely be checking out that link first thing in the morning.

回答1:

UPDATE: installation without root privileges below

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I advise you to not install packages manually on ubuntu system if there is already a (semi-official) repository able to solve your problem. Further, use Oracle JDK for development, just to avoid (very sporadic) compatibility issues (i've tried many years ago, it's surely better now).

Add the webupd8 repo to your system:

sudo add-apt-repository ppa:webupd8team/java sudo apt-get update 

Install your preferred version of jdk (versions from java-6 to java-9 available):

sudo apt-get install oracle-java8-installer 

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You can also install multiple version of jdk, mixing openjdk and oracle versions. Then you can use the command update-java-alternatives to switch between installed version:

# list available jdk update-java-alternatives --list  # use jdk7 sudo update-java-alternatives --set java-7-oracle  # use jdk8 sudo update-java-alternatives --set java-8-oracle 

Requirements

If you get add-apt-repository: command not found be sure to have software-properties-common installed:

sudo apt-get install software-properties-common 

If you're using an older version Ubuntu:

sudo apt-get install python-software-properties 

---

JDK installation without root privileges

If you haven't administrator rights on your target machine your simplest bet is to use sdkman to install the zulu certified openjdk:

curl -s "https://get.sdkman.io" | bash source "$HOME/.sdkman/bin/sdkman-init.sh" sdk install java 

NOTE: sdkman allow to install also the official Oracle JDK, although it's not a the default option. View available versions with:

sdk ls java 

Install the chosen version with:

sdk install java 

For example:

sdk install java 9.0.1-oracle 

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Glossary of commands

• sudo [command_arguments]: execute a command with the superuser privilege.

• add-apt-repository : Ubuntu (just like every Debian derivatives and generally speaking every Linux distribution) has a main repository of packages that handle things like package dependencies and updating. In Ubuntu is possible to extend the main repository using a PPA (Personal Package Archive) that usually contains packages not available in the system (just like oracle jdk) or updated versions of available ones (example: LibreOffice 5 in LTS is available only through this PPA).

• apt-get [install|update|upgrade|purge|...]: it's "the" command-line package handler used to manipulate the state of every repository on the system (installing / updating / upgrading can be viewed as an alteration of the repository current state).

In our case: with the command sudo add-apt-repository ppa:webupd8team/java we inform the system that the next repository update must retrieve packages information also from webupd8 repo.

With sudo apt-get update we actually update the system repository (all this operations requires superuser privileges, so we prepend sudo to the commands).

sudo apt-get install oracle-java8-installer

• update-java-alternatives (a specific java version of update-alternatives): in Ubuntu several packages provides the same functionality (browse the internet, compile mails, edit a text file or provides java/javac executables...). To allows the system to choose the user favourites tool given a specific task a mechanism using symlinks under /etc/alternatives/ is used. Try to update the jdk as indicated above (switch between java 7 and java 8) and view how change the output of this command:

  ls -l /etc/alternatives/java*

In our case: sudo update-java-alternatives --set java-8-oracle update symlinks under /etc/alternatives to point to java-8-oracle executables.

Extras:

• man : start using man to read a really well written and detailed help on (almost) every shell command and its options (every command i mention in this little answer has a man page, try man update-java-alternatives).

• apt-cache search : query the APT cache to search for a package related with the search_key provided (can be the package name or some word in package description).

• apt-cache show : provides APT information for a specific package (package version, installed or not, description).

回答2:

As you can see I only have java 1.7 installed (on a Ubuntu 14.04 machine).

update-java-alternatives -l java-1.7.0-openjdk-amd64 1071 /usr/lib/jvm/java-1.7.0-openjdk-amd64 

To install Java 8, I did,

sudo add-apt-repository ppa:openjdk-r/ppa sudo apt-get update sudo apt-get install openjdk-8-jdk 

Afterwards, now I have java 7 and 8,

update-java-alternatives -l java-1.7.0-openjdk-amd64 1071 /usr/lib/jvm/java-1.7.0-openjdk-amd64 java-1.8.0-openjdk-amd64 1069 /usr/lib/jvm/java-1.8.0-openjdk-amd64 

BONUS ADDED (how to switch between different versions)

• run the follwing command from the terminal:

sudo update-alternatives --config java

There are 2 choices for the alternative java (providing /usr/bin/java).    Selection    Path                                            Priority   Status ------------------------------------------------------------   0            /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java   1071      auto mode   1            /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java   1071      manual mode * 2            /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java   1069      manual mode  Press enter to keep the current choice[*], or type selection number: 

As you can see I'm running open jdk 8. To switch to to jdk 7, press 1 and hit the Enter key. Do the same for javac as well with, sudo update-alternatives --config javac.

Check versions to confirm the change: java -version and javac -version.

回答3:

I'm getting OpenJDK 8 from the official Debian repositories, rather than some random PPA or non-free Oracle binary. Here's how I did it:

sudo apt-get install debian-keyring debian-archive-keyring

Make /etc/apt/sources.list.d/debian-jessie-backports.list:

deb http://httpredir.debian.org/debian/ jessie-backports main 

Make /etc/apt/preferences.d/debian-jessie-backports:

Package: * Pin: release o=Debian,a=jessie-backports Pin-Priority: -200 

Then finally do the install:

sudo apt-get update sudo apt-get -t jessie-backports install openjdk-8-jdk 

文章来源: Ubuntu: OpenJDK 8 - Unable to locate package