Jar programs. How to open a .JAR file? Saving to JAR

The most common problem that prevents users from opening this file is an incorrectly assigned program.

To fix this in Windows OS, you need to right-click on the file, in the context menu, hover the mouse over the “Open with” item, and select “Select a program...” from the drop-down menu. As a result, you will see a list of installed programs on your computer, and you can select the appropriate one. We also recommend checking the box next to “Use this application for all JAR files.”

• Another problem that our users also encounter quite often is that the JAR file is corrupted.
• This situation can arise in many cases. For example: the file was downloaded incompletely as a result of a server error, the file was damaged initially, etc. To resolve this problem, use one of the recommendations:

Try finding the file you need in another source on the Internet. You may have luck finding a more suitable version. Example Google search: "File filetype:JAR" . Just replace the word "file" with the name you want; Ask them to send you the original file again, it may have been damaged during transmission;

JAR file

- an application or game for older mobile phones that supports Java, as well as Jar files are used in the Mozilla Firefox browser as themes and add-ons.

The JAR format is familiar to those who use Java for work or play. This extension includes different classes of java files. It also contains other resources that are related to programs and applications. They can be images, texts or something else.

The developers were inspired to create the JAR format by the ZIP extension. Files with this format are created in different ways, for example, they can be made using special tools and jar commands. The resulting archive can be digitally signed for greater reliability. It is created using the jarsign tools. Files with this extension are in great demand among users and are widely used.

The Java Archive is more than just a collection of classes

For most Java developers, JAR files and their specialized cousins ​​WAR and EAR files are simply the end result of a long process of working in Ant or Maven. The standard procedure is to copy the JAR to the desired location on the server (or, less commonly, on the user's computer) and forget about it.

In fact, JAR files are good for more than just storing source code. You just need to know their capabilities and how to implement these capabilities. Tips in this episode Five secrets, will help you get the most out of your Java archive files (and in some cases also WAR/EAR files), especially during the deployment process.

Because many Java developers use Spring (and because the Spring framework presents some challenges to traditional JAR file usage), some of the tips specifically apply to JAR files in Spring applications.

About this series of articles

Do you think you know everything about Java programming? In reality, most developers are just scratching the surface of the Java platform, learning just enough about it to get the job done. Here, Ted Neward dives deep into the functionality of the Java platform, revealing little-known facts that can help solve the trickiest programming problems.

I'll start with a quick example of a standard procedure for working with Java Archive files, which will serve as the basis for the tips that follow.

Saving to JAR

Typically, a JAR file is created after source code has been compiled to assemble the Java code (which is separate from the package) into a single collection using the jar command line utility or, more commonly, the Ant jar task. This process is simple enough that I won't demonstrate it here, although we will return to the topic of JAR file design later. For now, we just need to archive Hello, a separate console utility that performs the incredibly useful task of printing a message to the console, as shown in Listing 1.

Listing 1. Archiving the console utility

The Hello utility doesn't do much, but it's a useful example for learning about JAR files, starting with executing the code.

1. JAR files are executable

Historically, languages ​​like .NET and C++ have had the advantage of being OS-friendly: launching an application is as simple as typing its name at the command line (helloWorld.exe) or double-clicking its icon in the graphical user interface (GUI) shell. In Java programming, the application launcher - java - loads into the JVM process and needs to be passed a command line argument (com.tedneward.Hello) indicating the class whose main() method we want to run.

These extra steps make it difficult to create user-friendly Java applications. All of these items need to be typed on the command line, which many end users try to avoid, and very often things go wrong, resulting in strange error messages.

You can get around this by making the JAR file "executable" so that when it is executed, the Java launcher automatically knows which class to run. To do this, just enter the following entry into the JAR file manifest (MANIFEST.MF in the JAR META-INF archive subdirectory).

Listing 2. Specifying the entry point

A manifest is simply a collection of name/value pairs. Sometimes the manifest can get nitpicky about space and return characters, so the easiest way is to use Ant to create it. Listing 3 uses the manifest element of the Ant jar task to define the manifest.

Listing 3. Creating an entry point

Now, to execute a JAR file, the user just needs to enter its name into the command line using the java -jar outapp.jar command. In some GUI shells, this can also be done by double-clicking on the JAR file.

2. JAR files may include dependency information

With the growing popularity of the Hello utility, it became necessary to vary its implementation. Many details of this process are handled by Dependency Injection (DI) containers such as Spring or Guice, but there is a catch: changing the code to enable the DI container can produce results similar to the one in Listing 4.

Listing 4. Hello, world of Spring!

The launcher's -jar option overrides anything in the -classpath command line option, so Spring must be present in the CLASSPATH when running this code And in the environment variable. Fortunately, JAR files allow other JAR dependencies to be declared in the manifest, which implicitly create a CLASSPATH without having to declare it, as shown in Listing 5.

Listing 5. Hello, Spring CLASSPATH!

Note that the Class-Path attribute contains a relative reference to the JAR files that the application depends on. This can be written as an absolute reference or without a prefix at all, assuming that the JAR files are in the same directory as the application JAR.

Unfortunately, the value attribute of the Class-Path Ant attribute must be on the same line because the JAR manifest cannot handle multiple Class-Path attributes. So all these dependencies should be on one line in the manifest file. Of course it's ugly, but being able to write java -jar outapp.jar is worth it!

3. JAR files can be referenced implicitly

When there are several different command line utilities (or other applications) that use the Spring framework, it is convenient to place the Spring JAR files in a common folder through which all of these utilities can be referenced. This will avoid having to deal with multiple copies of JAR files scattered throughout the file system. By default, this location is the normal location of the Java runtime for JAR files, the so-called. "extension directory" which is located in the lib/ext subdirectory of the JRE installation directory.

The location of the JRE can be changed, but this is rarely done, so for a given Java environment it is quite safe to assume that lib/ext is a safe place to store JAR files and that they will be implicitly present in the Java environment's CLASSPATH.

4. Java 6 allows wildcards in classpath

To avoid cumbersome CLASSPATH environment variables (which Java developers should have abandoned years ago) and/or -classpath command line options, Java 6 introduced the concept classpath wildcard. Instead of running every JAR file explicitly specified in the argument, classpath wildcards allow you to write lib/* and all JAR files listed in that directory will go into the classpath (not recursively).

Unfortunately, classpath wildcards are not supported in the manifest Class-Path attribute entry discussed above. But they make it easier to run Java applications (including servers) for tasks such as working with code generation or analysis tools.

5. JAR files contain more than just code

Spring, like many other parts of the Java ecosystem, depends on a configuration file to define how the environment is organized. Namely, Spring depends on an app.xml file, which is located in the same directory as the JAR file - but developers often forget to copy the configuration file along with the JAR file.

Some configuration files are edited by the system administrator, but a significant number of them (for example, the composition of the Hibernate library) are outside his control, which leads to errors during deployment. A smart solution is to package the configuration file along with the code - and this is doable because a JAR is basically a ZIP in disguise. Just when building the JAR, include the configuration files in the Ant task or jar command line.

JAR files can contain other types of files in addition to configuration files. For example, if my SpeakEnglish component needed to access a properties file, I would do it something like Listing 6 shows.

Listing 6. Custom response

Putting responses.properties in a JAR file means there is one less file to worry about when deploying alongside the JAR files. To do this, simply include the responses.properties file when creating the JAR.

However, how can we get back those properties that are stored in the JAR file? If the data you want is located inside the same JAR file, as in the previous example, you don't necessarily have to try to remember the location of that JAR file and open it using the JarFile object. Instead, let the ClassLoader of the class find it as a "resource" within the JAR file by using the ClassLoader getResourceAsStream() method, as shown in Listing 7.

Listing 7. ClassLoader finds a resource

This procedure works with resources of any kind: configuration files, audio files, graphic files, etc. Almost any type of file can be placed in a JAR, obtained as an InputStream (via ClassLoader), and used in any way.

Conclusion

This article reveals five secrets of JAR files that are usually hidden from most Java developers - at least based on history and anecdotes. Please note that all tips related to JAR files are fully valid for WAR files. Some of them (particularly the Class-Path and Main-Class attributes) are not as useful in the case of WAR files, because the servlet framework itself collects all the contents of the directory and has a predefined entry point. However, taken together, these tips take us beyond the paradigm of “Let's start by copying everything into this directory...” They also greatly simplify the process of deploying Java applications.

The next article in this series: “Five secrets for monitoring Java application performance.”

In this article we will talk in detail about jar files. You will learn how to open a file in jar format, what programs are needed for this, as well as a lot of useful information.

Figure 1. Window for selecting a .jar file to open

What is jar file format

The Java ARchive extension is a special archive with applications. In simple terms, it is a ZIP document that is enhanced with certain functions. How to use it on different devices?

How to run a file in windows

On the Windows operating system, you can run the jar file using special programs. Let's list the main options.

Oracle Java Runtime Environment

This is an application that allows you to view documents on your personal computer. You will be able to work even with those games that flatly refuse to “cooperate” with standard programs.

Eclipse

This is a free development that was created to work with this format. A simple and clear menu will not cause problems or difficulties. A novice user will understand it, because everything is laid out on the shelves.

7-Zip

This archiver will help you figure out how to open a jar file. Suitable for using documents with the appropriate format (Figure 2). The fully functional application is available for free download. You can download the program on our website.

Figure 2. Appearance of the 7-zip program interface for working with jar files

WinRAR

This archiver can handle most extensions. It makes it much more convenient to understand how to run a jar file (Figure 3). The product is used on different platforms.

Figure 3. Working interface of the WinRaR application for working with .jar files

IZArc

A free program that supports working with docks of different formats. Very simple and understandable development. The interface is thought out to the smallest detail. The program is available on our website.

WinZIP

Another fairly common archiver that is designed for expansion. can be downloaded from our website. It features excellent memory compression, so it is possible to save space on your hard drive (Figure 4). The package is offered in different versions, which allows you to choose the appropriate option for your equipment.

Figure 4. Appearance of the unpacked file window in the WinZIP application

ZipZag

Working with archives will be comfortable and simple. Each menu item is understandable for a user with little experience. You will be able to view formatted documents without encountering problems.

Java Development Kit

The interactive package is designed specifically for such extensions. This is a complete set of tools that perform useful functions.

Now you know how to run a jar file in Windows using special packages.

How to run a file on Linux

Linux is an operating system on which similar formats are also often used. See how to run a linux jar file without facing any problems.

Eclipse

The simplest and most accessible option for every user. With it you can quickly download what you need without encountering all sorts of difficulties. You don't have to pay to download the package.

Java Runtime Environment

It allows you to run applications that are written in Java. The platform is suitable for use on devices running the Linux operating system.

Running a jar file on MacOS

There are also packages for this OS that make it possible to enjoy your favorite games and other applets.

Apple Jar Launcher

An excellent package with which launching a jar file will be quick. Working with it is simple and straightforward. Users can easily navigate the menu.

File Viewer

A universal program that allows you to view the contents of documents with different formats. Perfectly suited for this operating system.

How to open a file using java?

You don't know how to open a jar file using java? There are many Java applications available for viewing documents. You can choose what suits your operating system. Study the characteristics of each option to choose the optimal package for your gadget.

If you are looking for how to open a jar file on your computer, check out the methods above. Among them you will definitely take note of something!

JAR (Java Archive File) is an archive format that stores elements of a program written in the Java language. Most often, files with this extension are mobile games and applications. On your computer, you can view the contents of such an archive and/or try to run the JAR as an application.

First, let's look at several programs for opening a JAR archive. This way you can make sure that it contains everything you need to run this application, and also make the required changes.

Method 1: WinRAR

When it comes to archives, the WinRAR program comes to mind for most users. It works great for opening a JAR file.

Please note that there is a folder "META-INF" and file "MANIFEST.MF", which should be stored in it. This will allow the JAR file to be implemented as executable.

You can also find and open the desired archive through the built-in WinRAR file browser.

If further work is planned with the contents of the archive, then unarchiving will be required.

Method 2: 7-Zip

Support for the JAR extension is also provided in the 7-Zip archiver.

Method 3: Total Commander

An alternative to the programs mentioned can be the Total Commander file manager. Because its functionality includes working with archives; opening a JAR file will not be difficult.

Ways to run JAR on a computer

If you need to run a JAR application or game, you will need one of the special emulators.

Method 1: KEmulator

The KEmulator program is an advanced Java emulator that allows you to configure various application launch parameters.

On mobile phones, control was carried out using the keyboard. In KEmulator you can enable its virtual analogue: click "Reference" and select "Keyboard".

It will look like this:

If you wish, in the program settings you can set the correspondence between the phone keys and the computer keys.

Please note that a file will appear in the JAR folder "kemulator.cfg", which specifies the operating parameters of this application. If you delete it, then all settings and saves (if we are talking about the game) will be deleted.

Method 2: MidpX

The MidpX program is not as functional as KEmulator, but it gets the job done.

Once installed, all JAR files will be associated with MidpX. This can be understood by the changed icon:

Double click on it and the application will be launched. At the same time, the virtual keyboard is already integrated into the program interface, but you cannot configure control from the PC keyboard here.

Method 3: Sjboy Emulator

Another simple option for running JAR is Sjboy Emulator. Its main feature is the ability to select skins.

The keyboard is also integrated here.

So, we found out that JAR can be opened not only as a regular archive, but also run on a computer through a Java emulator. In the latter case, it is most convenient to use KEmulator, although other options also have their advantages, for example, the ability to change the window design.