Updating class file in jar

Question

I want to update a  class file in a jar with a new one  What is the easiest way to do it  especially in the Eclipse IDE

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1  you can extract the file into a folder called      jarname jar   and then replace the file in the folder  handy if you are updating the class a lot while debugging  2  you can extract the jar replace the file then the jar it up again  3  Open the jar with 7 zip and drag and drop your new class in to copy over the old one

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This tutorial details how to update a jar file  jar -uf jar-file  lt optional folder structure gt  input-file s         where  u  means update

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You can find source code of any  jar file online  import the same project in your IDE with basic setups  Make necessary changes in  java file and compile it for  class files   Once compilation is done You need to extract the jar file  replace the old  class file with new one   And use below command for reconstruct  jar file  Jar cf test jar    Note   I have done so many time this changes in our project  hope you will find it useful

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A JAR file is just a  zip in disguise  The zipped folder contains  class files   If you re on macOS    Rename the file to possess the   zip  extension  e g  myJar jar -  myJar zip  Decompress the   zip   double click on it   A new folder called  myJar  will appear Find and replace the  class file with your new  class file  Select all the contents of the folder  myJar  and choose  Compress x items   DO NOT ZIP THE FOLDER ITSELF  ONLY ITS CONTENTS   Miscellaneous - Compiling a single  class file  with reference to a original jar  on macOS   Make a file myClass java  containing your code  Open terminal from Spotlight  javac -classpath originalJar jar myClass java This will create your compiled class called myClass class    From here  follow the steps above  You can also use Eclipse to compile it  simply reference the original jar by right clicking on the project   Build Path  -   Add External Archives   From here you should be able to compile it as a jar  and use the zip technique above to retrieve the class from the jar

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High-level steps   Setup the environment Use JD-GUI to peek into the JAR file Unpack the JAR file Modify the  class file with a Java Bytecode Editor Update the modified classes into existing JAR file Verify it with JD-GUI   Refer below link for detailed steps and methods to do it   https   www talksinfo com how-to-edit-class-file-from-a-jar

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Editing properties my app properties file inside jar    zip -u  var opt my-jar-with-dependencies jar properties my app properties   Basically  zip -u  lt source gt   lt dest gt    where dest is relative to the jar extract folder

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Jar is an archive  you can replace a file in it by yourself in your favourite file manager  Total Commander for example

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Use jar -xvf to extract the files to a directory  Make your changes and replace the classes  Use jar -cvf to create a new jar file

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Do you want to do it automatically or manually   If manually  a JAR file is really just a ZIP file  so you should be able to open it with any ZIP reader    You may need to change the extension first    If you want to update the JAR file automatically via Eclipse  you may want to look into Ant support in Eclipse and look at the zip task

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Simply drag and drop your new class file to the JAR using 7-Zip or Winzip  You can even modify a JAR file that is included in a WAR file using the parent folder icon  and click Ok when 7zip detects that the inside file has been modified

User · Answer

An alternative is not to replace the  class file in the jar file  Instead put it into a new jar file and ensure that it appears earlier on your classpath than the original jar file    Not sure I would recommend this for production software but for development it is quick and easy

[java] Updating .class file in jar

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