1. What is Lombok

• Official website: https://projectlombok.org/

• Project Lombok is a java library that automatically plugs into your editor and build tools, spicing up your java. Never write another getter or equals method again, with one annotation your class has a fully featured builder, Automate your logging variables, and much more.

• Colloquialism: Lombok is a kind of Java ™ Utility tools can be used to help developers eliminate verbose code in Java, especially for simple Java objects (POJO s), which achieve this through annotations.

• Simplify JavaBean development

<dependency>
	<groupid>org.projectlombok</groupid>
	<artifactid>lombok</artifactid>
</dependency>

• Search and install lombok plug-in in idea
• Lombok @Data annotation
• Press the shortcut key Alt+7 to display all methods and global constants in the current class. The method also includes formal parameters and return values
• Or view -- > tool windows -- > structure -- > Click

2. Lombok principle

• JSR 269: Pluggable Annotation Processing API
• Official website: https://www.jcp.org/en/jsr/detail?id=269 JDK6 provides features that use annotations during Javac compilation
• View the compiled user class
• Principle implementation flow chart

3. Common notes of Lombok

1. @Getter And @ Setter method

• Test @Setter annotation user java User.class

• Test @ Getter(AccessLevel.PROTECTED) annotation. The default is public. You can set the level of different methods

• Add set and get methods to all variables and annotate them directly in the class

• be careful:

  1. lombok will not generate set and get methods for static modified variables
  2. lombok will not generate set method for final modified characters

• Custom variables do not generate set and get methods

2. @ToString method

• Custom ToString method to exclude some fields

3. @EqualsAndHashCode

• Customize the EqualsAndHashCode method that excludes some fields

4. @NonNull

• Function: the function of annotation is to make a non empty judgment in the method
• Case:

public void test(@NonNull String s){
        System.out.println(s);
}
public static void main(String[] args) {
        User user = new User();
        user.test(null);
    }

• Result: null pointer
• View compiled source code:

public void test(@NonNull String s) {
        if (s == null) {
            throw new NullPointerException("s is marked non-null but is null");
        } else {
            System.out.println(s);
        }
    }

• It can also be used in the constructor or annotated in the field

@NotNull private Integer id;

5. @NoArgsConstructor, @ RequiredArgsConstructor, @ AllArgsConstructor

• @NoArgsConstructor, add parameterless construction method

• @RequiredArgsConstructor, which specifies part of the parameterized construction. By default, it will find the variable with @ NonNull to add the construction method, or the variable with final modification and no initial value to add the construction method

• @AllArgsConstructor, which generates the construction method of all member variables

6. @Data

• Acting on a class, it is a collection of the following annotations: @ ToString, @ EqualsAndHashCode, @ Getter, @ Setter @RequiredArgsConstructor

7. @Builder

• Construct a series of methods with the field name as the method name, and the object returned by the method is UserBuilder

8. @Log

• @Log: acts on a class to generate log variables. There are different annotations for different log implementations:

9. val

HashMap<string,string> map = new HashMap<string,string>();

Simplified writing

val map = new HashMap<string,string>();

public static void main(String[] args) {
    val sets = new HashSet<string>();
    val lists = new ArrayList<string>();
    val maps = new HashMap<string, string>();
    //=> Equivalent to the following
    final Set<string> sets2 = new HashSet&lt;&gt;();
    final List<string> lists2 = new ArrayList&lt;&gt;();
    final Map<string, string> maps2 = new HashMap&lt;&gt;();
}

10. @Cleanup

• It is used to close and release resources and can be used on IO streams;

public class CleanupExample {
    public static void main(String[] args) throws IOException {
        @Cleanup InputStream in = new FileInputStream(args[0]);
        @Cleanup OutputStream out = new FileOutputStream(args[1]);
        byte[] b = new byte[10000];
        while (true) {
            int r = in.read(b);
            if (r == -1) break;
            out.write(b, 0, r);
        }
    }
}

• The above is equivalent to the following traditional Java code:

public class CleanupExample {
  public static void main(String[] args) throws IOException {
    InputStream in = new FileInputStream(args[0]);
    try {
      OutputStream out = new FileOutputStream(args[1]);
      try {
        byte[] b = new byte[10000];
        while (true) {
          int r = in.read(b);
          if (r == -1) break;
          out.write(b, 0, r);
        }
      } finally {
        if (out != null) {
          out.close();
        }
      }
    } finally {
      if (in != null) {
        in.close();
      }
    }
  }
}

4. Summary

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