Classloader in Java is an object that loads the dot class file. It takes the responsibility for loading classes into JVM.
Before compiling the program, the files are in dot Java file format. Whereas after program compilation, they convert into dot class files.
Role of Classloader in Java during Program Execution
Classloader in Java Loads the Dot Class Files into JVM
Classloader plays an important role, especially during program execution. It is an object that helps load classes necessary for program execution. The classloader fetches files from two sources: the local file and the other from various network sources. However, during execution, the classloader in Java prefers the local files over files from other sources. As a result, it executes the local files first.
Offers Security
To distinguish the local files from those fetched from other networks, separate “namespaces” are assigned for the classes of all local files. Thus, it uses different namespaces to manage files from the local file system and other network sources. By doing so, it adds security to the files.
Finally, after loading all the local classes, the memory layout of executable files is determined during the run time.
The Working of Classloader in Java: A Step-by-Step Explanation
What are the resources for the classlaoder? What kind of files will the classloader load?
Files that are in the dot class format are the resources for the classloader in Java.
How will the ClassLoader Initiate?
The classloader drags the dot class file from the secondary memory to the Java virtual machine.
By calling Java, the JRE gets the information it needs to initiate the execution. During the program execution, the dot class file or that particular command (the dot class file) is subjected to the classloader.
Process of Loading Files
Whenever you write a Java employee (java and class name), the Java virtual machine (JVM) gets information to invoke the JRE. Thereafter, it loads the dot class file into the JVM.
The invoking is possible through a classloader.
When the programmer writes Java and the class name, the classloader in Java fetches the dot class file. Either from the hard disk, mail, server, or pen drive (from any source).
After loading, it first goes to the bytecode verifier.
Why is it Necessary to Subject the Loaded File to Byte Code Verifier?
The loaded files need to load into the byte code verifier, which checks the files for security reasons.
What is the Need for Security at this Point of Programming?
We have seen that the classloader will fetch the dot class file from any source, like the server, pen drive, mail, etc., Whereas here, the source is unverified, and there are chances for threat to the computer. Due to security threats, the system may crash or hack. For example, files fetched from unverified sources can contain a program capable of hitting the C drive. During such times, security checks play an important role. They help avoid such trust issues and complications, especially while running programs from other sources.