Load the specified .class file, then parse out the class name, and then retransform the corresponding class loaded in the jvm. Every time a `.class` file is loaded, a retransform entry is recorded.
> If retransform is executed multiple times to load the same class file, there will be multiple retransform entries.
### View retransform entry
```bash
$ retransform -l
Id ClassName TransformCount LoaderHash LoaderClassName
1 demo.MathGame 1 null null
```
* TransformCount counts the times of attempts to return the .class file corresponding to the entry in the ClassFileTransformer#transform method, but it does not mean that the transform must be successful.
### Delete the specified retransform entry
Need to specify id:
```bash
retransform -d 1
```
### Delete all retransform entries
```bash
retransform --deleteAll
```
### Explicitly trigger retransform
```bash
$ retransform --classPattern demo.MathGame
retransform success, size: 1, classes:
demo.MathGame
```
> Note: For the same class, when there are multiple retransform entries, if retransform is explicitly triggered, the entry added last will take effect (the one with the largest id).
### Eliminate the influence of retransform
If you want to eliminate the impact after performing retransform on a class, you need to:
* Delete the retransform entry corresponding to this class
* Re-trigger retransform
> If you do not clear all retransform entries and trigger retransform again, the retransformed classes will still take effect when arthas stop.
* Use `jad` command to decompile bytecode, and then you can use other editors, such as vim to modify the source code.
* `mc` command to compile the modified code
* Load new bytecode with `retransform` command
### Tips for uploading .class files to the server
The `mc` command may fail. You can modify the code locally, compile it, and upload it to the server. Some servers do not allow direct uploading files, you can use the `base64` command to bypass.
1. Convert the `.class` file to base64 first, then save it as result.txt
```bash
Base64 < Test.class > result.txt
```
2. Login the server, create and edit `result.txt`, copy the local content, paste and save
3. Restore `result.txt` on the server to `.class`
```
Base64 -d < result.txt > Test.class
```
4. Use the md5 command to verify that the `.class` files are consistent.
### Restrictions of the retransform command
* New field/method is not allowed
* The function that is running, no exit can not take effect, such as the new `System.out.println` added below, only the `run()` function will take effect.
```java
public class MathGame {
public static void main(String[] args) throws InterruptedException {
MathGame game = new MathGame();
while (true) {
game.run();
TimeUnit.SECONDS.sleep(1);
// This doesn't work because the code keeps running in while
System.out.println("in loop");
}
}
public void run() throws InterruptedException {
// This works because the run() function ends completely every time
