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Week 113 — What is the jdeps tool and how can it be used?

Question of the Week #113
What is the jdeps tool and how can it be used?
4 Replies
dan1st | Daniel
dan1st | Daniel•3mo ago
jdeps is a tool that can be used to list dependencies between packages and modules. It can be run on JARs and directories containing class files. For example, assume a class Test in a package a: 
package a;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class Test{
    public static void main(String[] args) throws SQLException{
        Connection con = DriverManager.getConnection("jdbc:...");
        // TODO
    }
}
package a;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class Test{
    public static void main(String[] args) throws SQLException{
        Connection con = DriverManager.getConnection("jdbc:...");
        // TODO
    }
}
This class uses the java.sql module. After compiling it, it is possible to run the jdeps command with the compiled classes folder as its first and only argument (jdeps path/to/compiled/class/folder) and the output shows that code in the a package (the Test class) uses the java.lang and java.sql packages in their respective modules java.base and java.sql): 
. -> java.base
. -> java.sql
   a                                                  -> java.lang                                          java.base
   a                                                  -> java.sql                                           java.sql
. -> java.base
. -> java.sql
   a                                                  -> java.lang                                          java.base
   a                                                  -> java.sql                                           java.sql
We can also add a class in another package: 
package b;

import java.time.LocalDate;

public class Util{
    public static void displayCurrentDate(){
        System.out.println(LocalDate.now());
    }
}
package b;

import java.time.LocalDate;

public class Util{
    public static void displayCurrentDate(){
        System.out.println(LocalDate.now());
    }
}
and change the Test class in the a package to use that class: 
package a;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

import b.Util;

public class Test{
    public static void main(String[] args) throws SQLException{
        Connection con = DriverManager.getConnection("jdbc:...");
        // TODO
        Util.displayCurrentDate();
    }
}
package a;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

import b.Util;

public class Test{
    public static void main(String[] args) throws SQLException{
        Connection con = DriverManager.getConnection("jdbc:...");
        // TODO
        Util.displayCurrentDate();
    }
}
When running jdeps again on the directory containing the compiled class files, it shows that a is using b and that b is accessing the packages java.lang, java.io and java.time: 
. -> java.base
. -> java.sql
   a                                                  -> b                                                  .
   a                                                  -> java.lang                                          java.base
   a                                                  -> java.sql                                           java.sql
   b                                                  -> java.io                                            java.base
   b                                                  -> java.lang                                          java.base
   b                                                  -> java.time                                          java.base
. -> java.base
. -> java.sql
   a                                                  -> b                                                  .
   a                                                  -> java.lang                                          java.base
   a                                                  -> java.sql                                           java.sql
   b                                                  -> java.io                                            java.base
   b                                                  -> java.lang                                          java.base
   b                                                  -> java.time                                          java.base
dan1st | Daniel
dan1st | Daniel•3mo ago
The jdeps command is also capable of generating a simple module-info.java file requiring all dependenceis used by a JAR at compile-time. This is possible using the --generate-module-info command followed by the directory the module-info.java file should be generated in. The following commands generate a JAR named project.jar from the classes above (assuming they were compiled to directories a and b for the two packages) and generates a module-info.java file for it in generated/project/module-info.java 
jar cfe project.jar a.Test a b
jdeps --generate-module-info generated project.jar
jar cfe project.jar a.Test a b
jdeps --generate-module-info generated project.jar
The generated module-info.java would look similar to the following: 
module project {
    requires transitive java.sql;

    exports a;
    exports b;

}
module project {
    requires transitive java.sql;

    exports a;
    exports b;

}
📖 Sample answer from dan1st
dan1st | Daniel
dan1st | Daniel•3mo ago
Jdeps command shows the package level or class level dependencies of Java class files it is used to launch the Java class analyzee
dan1st | Daniel
dan1st | Daniel•3mo ago
Analyser
Submission from shambhavi2332

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