Version: v1.5.x

Code style and quality guide

1 Pull Requests & Changes Rule

ISSUE/PR(pull request) driving and naming
- After creating a new PR, you need to associate the existing corresponding ISSUE at the Github Development button on the PR page (if there is no corresponding ISSUE, it is recommended to create a new corresponding ISSUE).
- Title naming format
  [feature/bugfix/doc/improve/refactor/bug/cleanup] title
Description
- Please fill in the PR template to describe the contribution. So that the reviewer can understand the problem and solution from the description, rather than just from the code.
- Check the CheckList
It's recommended that PR should be arranged changes such as cleanup, Refactor, improve, and feature into separated PRs/Commits.
Commit message(English, lowercase, no special characters)
The commit of messages should follow a pattern similar to the [feature/bugfix/doc/improve/refactor/bug/cleanup] title

2 Code Checkstyle

2.1 Configure Checkstyle

Install the Checkstyle-IDEA plugin.
Open Checkstyle Settings. Click Settings → Tools → Checkstyle.
Set Checkstyle version to 10.14.2.
Set Scan scope to Only Java sources (including tests).
Click + button in the Configuration section to open a dialog to choose the checkstyle config file.
1. Enter a Description. For example, hertzbeat.
2. Select Use a local checkstyle file.
3. Set File to script/checkstyle/checkstyle.xml.
4. Select Store relative to project location.
5. Click Next → Next → Finish.
Activate the configuration you just added by toggling the corresponding box.
Click OK.

Backend code specification Maven plugin: checkstyle Just run mvn checkstyle:checkstyle.
Frontend code formatting plugin eslint Just run npm run lint:fix in web-app

3 Programming Specification

3.1 Naming Style

Prioritize selecting nouns for variable naming, it's easier to distinguish between variables or methods.
```
  Cache<String> publicKeyCache;
```
Pinyin abbreviations are prohibited for variables (excluding nouns such as place names), such as chengdu.
It is recommended to end variable names with a type.
For variables of type Collection/List, take xxxx (plural representing multiple elements) or end with xxxList (specific type).
For variables of type map, describe the key and value clearly:
```
  Map<Long, User> idUserMap;
  Map<Long, String> userIdNameMap;
```
That can intuitively know the type and meaning of the variable through its name.
Method names should start with a verb first as follows:
```
  void computeVcores(Object parameter1);
```
Note: It is not necessary to strictly follow this rule in the Builder tool class.

3.2 Constant Variables Definition

Redundant strings should be extracted as constants

If a constant has been hardcoded twice or more times, please directly extract it as a constant and change the corresponding reference. In generally, constants in log can be ignored to extract.

Negative demo:

public static RestResponse success(Object data) {
    RestResponse resp = new RestResponse();
    resp.put("status", "success");
    resp.put("code", ResponseCode.CODE_SUCCESS);
    resp.put("data", data);
    return resp;
}

public static RestResponse error() {
    RestResponse resp = new RestResponse();
    resp.put("status", "error");
    resp.put("code", ResponseCode.CODE_FAIL);
    resp.put("data", null);
    return resp;
}

Positive demo:

Strings are extracted as constant references.

  public static final String STATUS = "status";
  public static final String CODE = "code";
  public static final String DATA = "data";
  
  public static RestResponse success(Object data) {
      RestResponse resp = new RestResponse();
      resp.put(STATUS, "success");
      resp.put(CODE, ResponseCode.CODE_SUCCESS);
      resp.put(DATA, data);
      return resp;
  }
  
  public static RestResponse error() {
      RestResponse resp = new RestResponse();
      resp.put(STATUS, "error");
      resp.put(CODE, ResponseCode.CODE_FAIL);
      resp.put(DATA, null);
      return resp;
  }

Ensure code readability and intuitiveness

The string in the annotation symbol doesn't need to be extracted as constant.
The referenced package or resource name doesn't need to be extracted as constant.

Variables that have not been reassigned must also be declared as final types.
About the arrangement order of constant/variable lines
Sort the variable lines in the class in the order of
1. public static final V, static final V,protected static final V, private static final V
2. public static v, static v,protected static v, private static v
3. public v, v, protected v, private v

3.3 Methods Rule

Sort the methods in the class in the order of public, protected, private
Static methods of a class can be placed after non-static methods and sorted according to consistent method visibility.
When there are restrictions on the method, the parameters and returned values of the method need to be annotated with @Nonnull or @Nullable annotations and constraints.
For example, if the parameter cannot be null, it is best to add a @Nonnull annotation. If the returned value can be null, the @Nullable annotation should be added first.
Note: that the package name is javax.validation.requirements
If there are too many lines of code in the method, please have a try on using multiple sub methods at appropriate points to segment the method body.
Generally speaking, it needs to adhere to the following principles:
- Convenient testing
- Good semantics
- Easy to read
In addition, it is also necessary to consider whether the splitting is reasonable in terms of components, logic, abstraction, and other aspects in the scenario.
However, there is currently no clear definition of demo. During the evolution process, we will provide additional examples for developers to have a clearer reference and understanding.

3.4 Collection Rule

For collection returned values, unless there are special concurrent (such as thread safety), always return the interface, such as:
- returns List if use ArrayList
- returns Map if use HashMap
- returns Set if use HashSet
If there are multiple threads, the following declaration or returned types can be used:
```
  private CurrentHashMap map;
  public CurrentHashMap funName();
```

Use isEmpty() instead of length() == 0 or size() == 0

Negative demo：
```
if (pathPart.length() == 0) {
  return;
}
```
Positive demo：
```
if (pathPart.isEmpty()) {
  return;
}
```

3.5 Concurrent Processing

The thread pool needs to be managed, using a unified entry point to obtain the thread pool.
Note: During the evolution process, we will provide additional examples for developers to have a clearer reference and understanding.
Thread pool needs to be resource constrained to prevent resource leakage caused by improper handling

3.6 Control/Condition Statements

Avoid unreasonable condition/control branches order leads to:
- Multiple code line depths of n+1
- Redundant lines

Generally speaking, if a method's code line depth exceeds 2+ Tabs due to continuous nested if... else.., it should be considered to try

merging branches,
inverting branch conditions
extracting private methods

to reduce code line depth and improve readability like follows:

Union or merge the logic into the next level calling

Negative demo:

  if (isInsert) {
    save(platform);
  } else {
     updateById(platform);
  }

Positive demo:
```
  saveOrUpdate(platform);
```

Merge the conditions

Negative demo:

  if (expression1) {
    if(expression2) {
        ......
    }
  }

Positive demo:

 if (expression1 && expression2) {
   ......
 }

Reverse the condition

Negative demo:

  public void doSomething() {
   // Ignored more deeper block lines
   // .....
   if (condition1) {
      ...
   } else {
      ...
   }
  }

Positive demo:

  public void doSomething() {
   // Ignored more deeper block lines
   // .....
   if (!condition1) {
      ...
      return;
   }
   // ...
  }

Using a single variable or method to reduce the complex conditional expression

Negative demo:

  if (dbType.indexOf("sqlserver") >= 0 || dbType.indexOf("sql server") >= 0) {
   ...
  }

Positive demo:

  if (containsSqlServer(dbType)) {
    ....
  }
  //.....
  // definition of the containsSqlServer

Using sonarlint and better highlights to check code depth looks like good in the future.

3.7 Code Comments Rule

Method lacks comments:
- When: When can the method be called
- How: How to use this method and how to pass parameters, etc.
- What: What functions does this method achieve
- Note: What should developers pay attention to when calling this method
Missing necessary class header description comments.
Add What, Note, etc. like mentioned in the 1.
The method declaration in the interface must be annotated.
- If the semantics of the implementation and the annotation content at the interface declaration are inconsistent, the specific implementation method also needs to be rewritten with annotations.
- If the semantics of the method implementation are consistent with the annotation content at the interface declaration, it is not recommended to write annotations to avoid duplicate annotations.
The first word in the comment lines need to be capitalized, like param lines, return lines. If a special reference as a subject does not need to be capitalized, special symbols such as quotation marks need to be noted.

3.8 Java Lambdas

Prefer non-capturing lambdas (lambdas that do not contain references to the outer scope). Capturing lambdas need to create a new object instance for every call. Non-capturing lambdas can use the same instance for each invocation.
- Negative demo:
```
  map.computeIfAbsent(key, x -> key.toLowerCase())
```
- Positive demo:
```
 map.computeIfAbsent(key, k -> k.toLowerCase());
```

Consider method references instead of inline lambdas

Negative demo:

  map.computeIfAbsent(key, k-> Loader.load(k));

Positive demo:

  map.computeIfAbsent(key, Loader::load);

3.9 Java Streams

Avoid Java Streams in any performance critical code.
The main motivation to use Java Streams would be to improve code readability. As such, they can be a good match in parts of the code that are not data-intensive, but deal with coordination.
Even in the latter case, try to limit the scope to a method, or a few private methods within an internal class.

3.10 Pre-Conditions Checking

Use a unified Utils.requireXXX to complete the validation of the prerequisite, and if possible, replace the AlertXXException.throwIfXXX by new pre-conditions checking.

3.11 StringUtils

Use StringUtils.isBlank instead of StringUtils.isEmpty

Negative demo:

if (StringUtils.isEmpty(name)) {
return;
}

Positive demo:

if (StringUtils.isBlank(name)) {
return;
}

Use StringUtils.isNotBlank instead of StringUtils.isNotEmpty

Negative demo:

if (StringUtils.isNotEmpty(name)) {
  return;
}

Positive demo:

if (StringUtils.isNotBlank(name)) {
  return;
}

Use StringUtils.isAllBlank instead of StringUtils.isAllEmpty

Negative demo:

if (StringUtils.isAllEmpty(name, age)) {
  return;
}

Positive demo:

if (StringUtils.isAllBlank(name, age)) {
  return;
}

3.12 `Enum` Class

Enumeration value comparison

Negative demo:

if (status.equals(JobStatus.RUNNING)) {
  return;
}

Positive demo:

if (status == JobStatus.RUNNING) {
  return;
}

Enumeration classes do not need to implement Serializable

Negative demo:

public enum JobStatus implements Serializable {
  ...
}

Positive demo:
```
public enum JobStatus {
  ...
}
```

Use Enum.name() instead of Enum.toString()

Negative demo:

System.out.println(JobStatus.RUNNING.toString());

Positive demo:

System.out.println(JobStatus.RUNNING.name());

Enumeration class names uniformly use the Enum suffix
- Negative demo:
```
public enum JobStatus {
  ...
}
```
- Positive demo:
```
public enum JobStatusEnum {
  ...
}
```

3.13 `Deprecated` Annotation

Negative demo:

@deprecated
public void process(String input) {
  ...
}

Positive demo:

@Deprecated
public void process(String input) {
  ...
}

4 Log

Use placeholders for log output:

Negative demo

  log.info("Deploy cluster request " + deployRequest);

Positive demo

  log.info("load plugin:{} to {}", file.getName(), appPlugins);

Pay attention to the selection of log level when printing logs
When printing the log content, if the actual parameters of the log placeholder are passed, it is necessary to avoid premature evaluation to avoid unnecessary evaluation caused by the log level.
- Negative demo:
  Assuming the current log level is INFO:
```
 // ignored declaration lines.
 List<User> userList = getUsersByBatch(1000);
 LOG.debug("All users: {}", getAllUserIds(userList));
```
- Positive demo:
  In this case, we should determine the log level in advance before making actual log calls as follows:
```
 // ignored declaration lines.
 List<User> userList = getUsersByBatch(1000);
 if (LOG.isDebugEnabled()) {
   LOG.debug("All ids of users: {}", getAllIDsOfUsers(userList));   
 }
```

5 Testing

It's recommended to use JUnit5 to develop test case preparation
The implemented interface needs to write the e2e test case script under the e2e module.

1 Pull Requests & Changes Rule​

2 Code Checkstyle​

2.1 Configure Checkstyle​

3 Programming Specification​

3.1 Naming Style​

3.2 Constant Variables Definition​

3.3 Methods Rule​

3.4 Collection Rule​

3.5 Concurrent Processing​

3.6 Control/Condition Statements​

3.7 Code Comments Rule​

3.8 Java Lambdas​

3.9 Java Streams​

3.10 Pre-Conditions Checking​

3.11 StringUtils​

3.12 Enum Class​

3.13 Deprecated Annotation​

4 Log​

5 Testing​

References​

1 Pull Requests & Changes Rule

2 Code Checkstyle

2.1 Configure Checkstyle

3 Programming Specification

3.1 Naming Style

3.2 Constant Variables Definition

3.3 Methods Rule

3.4 Collection Rule

3.5 Concurrent Processing

3.6 Control/Condition Statements

3.7 Code Comments Rule

3.8 Java Lambdas

3.9 Java Streams

3.10 Pre-Conditions Checking

3.11 StringUtils

3.12 `Enum` Class

3.13 `Deprecated` Annotation

4 Log

5 Testing

References