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- [ ] I have searched the [issues](https://github.com/apache/dubbo/issues) of this repository and believe that this is not a duplicate.

### Environment

* Dubbo version: 2.7.7
* Operating System version: win10
* Java version: 1.8

### Steps to reproduce this issue

1. xxx
2. xxx
3. xxx

Pls. provide [GitHub address] to reproduce this issue.

### Expected Behavior

<!-- What do you expect from the above steps？-->

### Actual Behavior

<!-- What actually happens? -->

If there is an exception, please attach the exception trace:

```
Just put your stack trace here!
```

* RpcException cannot be extended, use error code for exception type to keep compatibility
     */
    private int code;
    public RpcException() {
        super();
    }
    public RpcException(String message, Throwable cause) {
        super(message, cause);
    }
    public RpcException(String message) {
        super(message);
    }
    public RpcException(Throwable cause) {
        super(cause);
    }
    public RpcException(int code) {
        super();
        this.code = code;
    }
    public RpcException(int code, String message, Throwable cause) {
        super(message, cause);
        this.code = code;
    }
    public RpcException(int code, String message) {
        super(message);
        this.code = code;
    }
    public RpcException(int code, Throwable cause) {
        super(cause);
        this.code = code;