[java] Java, How to add library files in netbeans?

I am new to the Netbeans IDE and Java. I have a java project that shows lot of compilation errors:

can not import "org.apache.commons.logging.Log"

Can somebody please help me with these errors, How do I add library files in Netbeans IDE?

For Netbeans 2020 September version. JDK 11

(Suggesting this for Gradle project only)

1. create libs folder in src/main/java folder of the project

2. copy past all library jars in there

3. open build.gradle in files tab of project window in project's root

4. correct main class (mine is mainClassName = 'uz.ManipulatorIkrom')

5. and in dependencies add next string:

apply plugin: 'java' 
apply plugin: 'jacoco' 
apply plugin: 'application'
description = 'testing netbeans'
mainClassName = 'uz.ManipulatorIkrom' //4th step
repositories {
    jcenter()
}
dependencies {
    implementation fileTree(dir: 'src/main/java/libs', include: '*.jar') //5th step   
}

6. save, clean-build and then run the app

In Netbeans 8.2

1. Dowload the binaries from the web source. The Apache Commos are in: [http://commons.apache.org/components.html][1] In this case, you must select the "Logging" in the Components menu and follow the link to downloads in the Releases part. Direct URL: [http://commons.apache.org/proper/commons-logging/download_logging.cgi][2] For me, the correct download was the file: commons-logging-1.2-bin.zip from the Binaries.

2. Unzip downloaded content. Now, you can see several jar files inside the directory created from the zip file.

3. Add the library to the project. Right click in the project, select Properties and click in Libraries (in the left side). Click the button "Add Jar/Folder". Go to the previously unzipped contents and select the properly jar file. Clic in "Open" and click in"Ok". The library has been loaded!

How to import a commons-library into netbeans.

1. Evaluate the error message in NetBeans:

   java.lang.NoClassDefFoundError: org/apache/commons/logging/LogFactory
   

2. NoClassDeffFoundError means somewhere under the hood in the code you used, a method called another method which invoked a class that cannot be found. So what that means is your code did this: MyFoobarClass foobar = new MyFoobarClass() and the compiler is confused because nowhere is defined this MyFoobarClass. This is why you get an error.

3. To know what to do next, you have to look at the error message closely. The words 'org/apache/commons' lets you know that this is the codebase that provides the tools you need. You have a choice, either you can import EVERYTHING in apache commons, or you could import JUST the LogFactory class, or you could do something in between. Like for example just get the logging bit of apache commons.

4. You'll want to go the middle of the road and get commons-logging. Excellent choice, fire up the google and search for apache commons-logging. The first link takes you to http://commons.apache.org/proper/commons-logging/. Go to downloads. There you will find the most up-to-date ones. If your project was compiled under ancient versions of commons-logging, then use those same ancient ones because if you use the newer ones, the code may fail because the newer versions are different.

5. You're going to want to download the commons-logging-1.1.3-bin.zip or something to that effect. Read what the name is saying. The .zip means it's a compressed file. commons-logging means that this one should contain the LogFactory class you desire. the middle 1.1.3 means that is the version. if you are compiling for an old version, you'll need to match these up, or else you risk the code not compiling right due to changes due to upgrading.

6. Download that zip. Unzip it. Search around for things that end in .jar. In netbeans right click your project, click properties, click libraries, click "add jar/folder" and import those jars. Save the project, and re-run, and the errors should be gone.

The binaries don't include the source code, so you won't be able to drill down and see what is happening when you debug. As programmers you should be downloading "the source" of apache commons and compiling from source, generating the jars yourself and importing those for experience. You should be smart enough to understand and correct the source code you are importing. These ancient versions of apache commons might have been compiled under an older version of Java, so if you go too far back, they may not even compile unless you compile them under an ancient version of java.