Working with and importing external libraries / fr

问题:

Firstly this is a very n00b question. But being a junior dev I've never needed to import and work with other Java Frameworks. The standard library was always good enough for me to write the classes I needed to write.

But now getting exposed to more "advanced" concepts, I need to start working with external frameworks, e.g. JSON for Java, Apache's HttpClient for java and so on. And I'm looking for a basic understanding on how this works and how to go about importing these libraries so you can start working with the classes...

So my initial understanding is that each of these fraemworks will provide you with a .jar file that contains all the classes for the framework. Which you then import into your project and lo and behold you'll be able to use the classes/library in your project by just importing it e.g. 'import org.json.*;'

Is the understanding correct?

回答1:

Correct.

You just add the libraries to your classpath and are now able to use classes from these libs. How you add the libs to your classpath depends on your actual development environment. If you use Apache Maven for example, you just have to define the dependencies (libs) in your projects pom.xml and Maven downloads them automatically for you.

hth,
- martin

回答2:

EDIT: The following only applies if you are not using automated build-tools like Maven or Ivy

Yes this is correct. To use a third party .jar file, download and place it in a convenient location (either system-wide or project-specific depending on your needs) and then include it in your classpath.

When executing from the command line do:

java -cp /path/to/library:. path.to.main

The :. is necessary so that the JVM will find your main method.

In an IDE you should be able to include the library in your classpath via the options menu.

Then you can just use the third party library like any other:

import name.of.library.class;
//Do something