Lombok常用註解及使用

說明：本文是博學谷課程整理的筆記，課程地址：https://xuexi.boxuegu.com/video.html?courseId=1586

lombok官網：https://projectlombok.org/

一、Lombok簡介

1. Lombok是什麼

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.

簡單說：

Lombok項目是一個Java實用工具庫，可以用來幫助開發人員消除Java中的冗長代碼，尤其是對於簡單的Java對象（POJO），它通過註解來實現這一目的。

2. Lombok原理

JSR 269：插件化註解處理API（Pluggable Annotation Processing API）——編譯期（SOURCE）註解，不同於運行期（RUNTIME）註解

官網：https://www.jcp.org/en/jsr/detail?id=269

JDK6提供的特性，在Javac編譯期利用註解搞事情！

3. Lombok安裝

3.1 javac

拷貝jar到類路徑
javac -cp lombok.jar ...

3.2 Maven

<!-- https://mvnrepository.com/artifact/org.projectlombok/lombok -->
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.12</version>
    <scope>provided</scope>
</dependency>

3.3 Intellij IDEA

官網：https://projectlombok.org/setup/intellij

Add the Lombok IntelliJ plugin to add lombok support for IntelliJ:

Go to File > Settings > Plugins

Click on Browse repositories...

Search for Lombok Plugin

Click on Install plugin

Restart IntelliJ IDEA

二、Lombok常用註解

1. @Getter/@Setter

package top.onefine.lombok;

import lombok.AccessLevel;
import lombok.Getter;
import lombok.Setter;

// 給所有類中的成員變量生成get/set方法
// 不對static類型產生效果
// 對final類型只會產生get方法，不會產生set方法
@Setter
@Getter
public class User {
	static String s = "";
    final int id2 = 10;
    // 只給id字段添加get/set方法
//    @Getter(AccessLevel.PROTECTED)  // 默認public
//    @Setter  // 默認public
    private Integer id;
    private String userName;
    private String password;
    private String phone;
    @Getter(AccessLevel.NONE)  // 不會生成對應的get方法，@Setter同理
    private String email;
}

2. @ToString

package top.onefine.lombok;

import lombok.ToString;

//@ToString  // 不會打印static類型的
//@ToString(exclude = {"email", "phone"})  // 不打印成員變量email和phone
@ToString(of = {"id2", "userName"})  // 只打印id和成員變量userName
public class User {
    static String s = "";  // 不會打印
    final int id2 = 10;
    private Integer id;
    private String userName;
    private String password;
    private String phone;
    private String email;
}

3. @EqualsAndHashCode

package top.onefine.lombok;

import lombok.EqualsAndHashCode;

//@EqualsAndHashCode  // 自動生成equals、canEqual、hashCode方法
//@EqualsAndHashCode(exclude = {"phone", "password"})  // 判斷時不比較phone和password字段
@EqualsAndHashCode(of = {"id"})  // 只根據id判斷
public class User {
    static String s = "";
    final int id2 = 10;
    private Integer id;
    private String userName;
    private String password;
    private String phone;
    private String email;
}

4. @NonNull

package top.onefine.lombok;

import lombok.NonNull;

public class User {
	@NonNull private Integer id;
	
    public void test(@NonNull String str) {  // 對實參str進行判斷，不允許其爲空
        System.out.println(str);
    }

    public static void main(String[] args) {
        new User().test(null);
    }
}

對class字節碼反編譯之後發現：

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

5. @NoArgsConstructor, @RequiredArgsConstructor, @AllArgsConstructor

package top.onefine.lombok;

import lombok.NoArgsConstructor;
import lombok.NonNull;
import lombok.RequiredArgsConstructor;

//@NoArgsConstructor  // 添加無參構造函數
@RequiredArgsConstructor  // 默認對標識NonNull註解或final關鍵字（不指定值的情況下；但是此時不能有無參的構造函數）的成員變量生成構造函數
public class User {
    static String s = "";
    final int id2;  // = 10;
    @NonNull private Integer id;
    private String userName;
    private String password;
    private String phone;
    private String email;
}

反編譯之後：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package top.onefine.lombok;

import lombok.NonNull;

public class User {
    static String s = "";
    final int id2;
    @NonNull
    private Integer id;
    private String userName;
    private String password;
    private String phone;
    private String email;

    public User(int id2, @NonNull Integer id) {
        if (id == null) {
            throw new NullPointerException("id is marked non-null but is null");
        } else {
            this.id2 = id2;
            this.id = id;
        }
    }
}

package top.onefine.lombok;

import lombok.AllArgsConstructor;
import lombok.NoArgsConstructor;
import lombok.NonNull;
import lombok.RequiredArgsConstructor;

//@NoArgsConstructor  // 添加無參構造函數
//@RequiredArgsConstructor  // 默認對標識NonNull註解或final關鍵字（不指定值的情況下；但是此時不能有無參的構造函數）的成員變量生成構造函數
@AllArgsConstructor  // 生成所有字段的構造函數
public class User {
    static String s = "";
    final int id2;  // = 10;
    @NonNull private Integer id;
    private String userName;
    private String password;
    private String phone;
    private String email;
}

反編譯之後：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package top.onefine.lombok;

import lombok.NonNull;

public class User {
    static String s = "";
    final int id2;
    @NonNull
    private Integer id;
    private String userName;
    private String password;
    private String phone;
    private String email;

    public User(int id2, @NonNull Integer id, String userName, String password, String phone, String email) {
        if (id == null) {
            throw new NullPointerException("id is marked non-null but is null");
        } else {
            this.id2 = id2;
            this.id = id;
            this.userName = userName;
            this.password = password;
            this.phone = phone;
            this.email = email;
        }
    }
}

6. @Data

package top.onefine.lombok;

import lombok.Data;
import lombok.NonNull;

@Data
public class User {
    static String s = "";
    final int id2; // = 10;
    @NonNull private Integer id;
    private String userName;
    private String password;
    private String phone;
    private String email;
}

直接上圖：

@Data集成了@Getter/@Setter、@ToString、@EqualsAndHashCode、@RequiredArgsConstructor四個註解。

7. @Builder

package top.onefine.lombok;

import lombok.Builder;
import lombok.NonNull;

@Builder
public class User {
    static String s = "";
    final int id2 = 10;
    @NonNull private Integer id;
    private String userName;
    private String password;
    private String phone;
    private String email;
}

直接上圖：

反編譯結果：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package top.onefine.lombok;

import lombok.NonNull;

public class User {
    static String s = "";
    final int id2 = 10;
    @NonNull
    private Integer id;
    private String userName;
    private String password;
    private String phone;
    private String email;

    User(@NonNull Integer id, String userName, String password, String phone, String email) {
        if (id == null) {
            throw new NullPointerException("id is marked non-null but is null");
        } else {
            this.id = id;
            this.userName = userName;
            this.password = password;
            this.phone = phone;
            this.email = email;
        }
    }

    public static top.onefine.lombok.User.UserBuilder builder() {
        return new top.onefine.lombok.User.UserBuilder();
    }
}

用法：

package top.onefine.lombok;

import lombok.Builder;
import lombok.NonNull;
import lombok.ToString;

@Builder
@ToString
public class User {
    static String s = "";
    final int id2 = 10;
    @NonNull private Integer id;
    private String userName;
    private String password;
    private String phone;
    private String email;

    public static void main(String[] args) {
        User user = User.builder().id(123).email("[email protected]").userName("one fine").build();// ...
        System.out.println(user);

    }
}

執行結果：

User(id2=10, id=123, userName=one fine, password=null, phone=null, [email protected])

8. @Log

package top.onefine.lombok;


import lombok.NonNull;
import lombok.extern.java.Log;

@Log
public class User {
    static String s = "";
    final int id2 = 10;
    @NonNull private Integer id;
    private String userName;
    private String password;
    private String phone;
    private String email;

    public static void main(String[] args) {
        log.info("info msg...");
    }

}

執行結果：

3月 09, 2020 11:29:31 下午 top.onefine.lombok.User main
信息: info msg...

反編譯之後：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package top.onefine.lombok;

import java.util.logging.Logger;
import lombok.NonNull;

public class User {
    private static final Logger log = Logger.getLogger(User.class.getName());
    static String s = "";
    final int id2 = 10;
    @NonNull
    private Integer id;
    private String userName;
    private String password;
    private String phone;
    private String email;

    public User() {
    }

    public static void main(String[] args) {
        log.info("info msg...");
    }
}

9. val

package top.onefine.lombok;

import java.util.HashMap;
import lombok.val;

public class User {

    public static void main(String[] args) {
//        HashMap<String, String> map = new HashMap<>();
        val map = new HashMap<String, String>();
        map.put("name", "one fine");
    }
}

反編譯後：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package top.onefine.lombok;

import java.util.HashMap;

public class User {
    public User() {
    }

    public static void main(String[] args) {
        HashMap<String, String> map = new HashMap();
        map.put("name", "one fine");
    }
}

10. @Cleanup

package top.onefine.lombok;

import java.io.*;

import lombok.Cleanup;

public class User {
    
    public static void main(String[] args) throws IOException {
        @Cleanup InputStream in = new FileInputStream("path1");  // 不用手動關閉
        @Cleanup OutputStream out = new FileOutputStream("path2");  // 不用手動關閉

        byte[] b = new byte[100];
        while (true) {
            int r = in.read(b);
            if (r == -1)
                break;
            out.write(b, 0, r);
        }
           
    }
}

字節碼反編譯之後：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package top.onefine.lombok;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Collections;

public class User {
    public User() {
    }

    public static void main(String[] args) throws IOException {
        FileInputStream in = new FileInputStream("path1");

        try {
            FileOutputStream out = new FileOutputStream("path2");

            try {
                byte[] b = new byte[100];

                while(true) {
                    int r = in.read(b);
                    if (r == -1) {
                        return;
                    }

                    out.write(b, 0, r);
                }
            } finally {
                if (Collections.singletonList(out).get(0) != null) {
                    out.close();
                }

            }
        } finally {
            if (Collections.singletonList(in).get(0) != null) {
                in.close();
            }

        }
    }
}

Lombok常用註解及使用

一、Lombok簡介

1. Lombok是什麼

2. Lombok原理

3. Lombok安裝

3.1 javac

3.2 Maven

3.3 Intellij IDEA

二、Lombok常用註解

1. @Getter/@Setter

2. @ToString

3. @EqualsAndHashCode

4. @NonNull

5. @NoArgsConstructor, @RequiredArgsConstructor, @AllArgsConstructor

6. @Data

7. @Builder

8. @Log

9. val

10. @Cleanup

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