Facing issue while chunking then merging the jar files

问题

I have one jar file for example apache-cassandra-3.11.6.jar. Firstly i split/chunked into mutiple jars like below :

apache-cassandra1.jar apache-cassandra2.jar apache-cassandra3.jar apache-cassandra4.jar apache-cassandra5.jar apache-cassandra6.jar

Then i reassemble them again into new Jar file i.e apache-cassandra_Merged.jar. Now the problem comes.

When i compare the original jar file i.e apache-cassandra-3.11.6.jar with new Jar file i.e apache-cassandra_Merged.jar. then it is not matching.

The newly created jar file which is apache-cassandra_Merged.jar, it's size also reduced.

Please find below my code for your reference :

/// Chunking/spliting into mutiple jars
Path path = Paths.get("/Original_Jar/apache-cassandra-3.11.6.jar");
byte [] data = Files.readAllBytes(path); // Will read all bytes at once

Now divide total bytes into equal part and then write in each small jars one by one.

int count = 0;
for(byte[] rangeData : Arrays.copyOfRange(data, rangeSTART, rangeEND)){
        FileOutputStream fileOutputStream1 = new FileOutputStream("/Cassandra_Image/Chunked_Jar/apache-cassandra"+count+".jar");
        fileOutputStream1.write(rangeData);
}

//Merging back to one jar For merging i used the same way. Created array of byte for each small/chunked jars and written into FileOutputStream("/Merged_Jar/apache-cassandra_Merged.jar") one by one.

Please let me know if i should use some other method/algorithm to split jar and reassemble it again which will make sure the originality of data after chunking and merging as well.

Note : Actually i want to transfer the jars to any server/directory where i should transfer a jar with limited size so for big size jars i need to split into small jars and send them one by one and then again reassemble them in target directory/place and it should be as original jar.

Thanks in advance.

回答1:

This may not be the answer, but I provide as an information for you. Java also provides pack format where you can compress the jar files and then you can uncompress using unpack. The tool is called pack200.

How to compress

<java_location>...\jre\lib>pack200 -J-Xmx256m small.jar.gz big.jar

How to uncompress

<java_location>...\jre\lib>unpack200 small.jar.gz big.jar

You can refer the following links.

https://docs.oracle.com/javase/1.5.0/docs/tooldocs/share/pack200.html

https://docs.oracle.com/javase/7/docs/technotes/tools/share/unpack200.html

回答2:

I am able to solve the issue with shell scripting. Written below code in my shell script file and run through my java code.

split -b 1000000 src.jar target.jar
cat src.jaraa src.jarab src.jarac src.jarad src.jarae > merged.jar

And compare with any algorithm like sha256 checksum will work fine and it shows equal. and size also equal.

来源：https://stackoverflow.com/questions/61815164/facing-issue-while-chunking-then-merging-the-jar-files