Step 1: Get the instance of ClassPool.
ClassPool pool = ClassPool.getDefault();
ClassPool is the root class that controls the byte code modifications. It is a container of CtClass objects (CtClass object represent a class file).
Step 2: Read class file from the source.
CtClass cc = pool.get("com.sample.app.model.Employee");
‘pool.get()’ method reads a class file from the source and returns a reference to the CtClass object representing that class file. If that class file has been already read, this method returns a reference to the CtClass created when that class file was read at the first time.
‘pool.get’ method searches the default system search path to find the class.
Step 3: Write the class file to a directory.
cc.writeFile("/Users/Shared/assistDemos");
Find the below working application.
Employee.java
package com.sample.app.model;
public class Employee {
private int id;
private String name;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
App.java
package com.sample.app;
import java.io.IOException;
import javassist.CannotCompileException;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.NotFoundException;
public class App {
public static void main(String args[]) throws NotFoundException, CannotCompileException, IOException {
ClassPool pool = ClassPool.getDefault();
CtClass cc = pool.get("com.sample.app.model.Employee");
cc.writeFile("/Users/Shared/assistDemos");
}
}
Run App.java
Open the directory '/Users/Shared/assistDemos', you can see Employee.class file is generated.
$tree /Users/Shared/assistDemos
/Users/Shared/assistDemos
└── com
└── sample
└── app
└── model
└── Employee.class
4 directories, 1 file
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