add code format descripition in contribution doc
@@ -40,6 +40,18 @@ Go to [issues page](https://github.com/FISCO-BCOS/web3sdk/issues)
7. Wait the community to review the code
8. Merged !!!!
+## Code formatting
+
+The code formatting tool are described by the [google-java-format-gradle-plugin](https://github.com/sherter/google-java-format-gradle-plugin).
+
+Execute the task `googleJavaFormat` to format all *.java files in the project
+```
+./gradlew goJF
+```
+Execute the task `verifyGoogleJavaFormat` to verify that all *.java files are formatted properly
+```
+./gradlew verGJF
+```
## Continous integration
