mirror of https://github.com/alibaba/arthas.git
You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
149 lines
4.7 KiB
Markdown
149 lines
4.7 KiB
Markdown
# retransform
|
|
|
|
[`mc-retransform` online tutorial](https://arthas.aliyun.com/doc/arthas-tutorials?language=en&id=command-mc-retransform)
|
|
|
|
::: tip
|
|
Load the external `*.class` files to retransform the loaded classes in JVM.
|
|
:::
|
|
|
|
Reference: [Instrumentation#retransformClasses](https://docs.oracle.com/javase/8/docs/api/java/lang/instrument/Instrumentation.html#retransformClasses-java.lang.Class...-)
|
|
|
|
## Usage
|
|
|
|
```bash
|
|
retransform /tmp/Test.class
|
|
retransform -l
|
|
retransform -d 1 # delete retransform entry
|
|
retransform --deleteAll # delete all retransform entries
|
|
retransform --classPattern demo.* # triger retransform classes
|
|
retransform -c 327a647b /tmp/Test.class /tmp/Test\$Inner.class
|
|
retransform --classLoaderClass 'sun.misc.Launcher$AppClassLoader' /tmp/Test.class
|
|
```
|
|
|
|
## retransform the specified .class file
|
|
|
|
```bash
|
|
$ retransform /tmp/MathGame.class
|
|
retransform success, size: 1, classes:
|
|
demo.MathGame
|
|
```
|
|
|
|
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.
|
|
|
|
::: tip
|
|
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
|
|
```
|
|
|
|
::: warning
|
|
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
|
|
|
|
::: tip
|
|
If you do not clear all retransform entries and trigger retransform again, the retransformed classes will still take effect when arthas stop.
|
|
:::
|
|
|
|
## Use with the jad/mc command
|
|
|
|
```bash
|
|
jad --source-only com.example.demo.arthas.user.UserController > /tmp/UserController.java
|
|
|
|
mc /tmp/UserController.java -d /tmp
|
|
|
|
retransform /tmp/com/example/demo/arthas/user/UserController.class
|
|
```
|
|
|
|
- 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
|
|
System.out.println("call run()");
|
|
try {
|
|
int number = random.nextInt();
|
|
List<Integer> primeFactors = primeFactors(number);
|
|
print(number, primeFactors);
|
|
|
|
} catch (Exception e) {
|
|
System.out.println(String.format("illegalArgumentCount:%3d, ", illegalArgumentCount) + e.getMessage());
|
|
}
|
|
}
|
|
}
|
|
```
|