lombok插件/slf4j中字符串格式化

大家在编写springboot项目的过程中可能会接触到lombok这个插件，这个插件可以在编译时帮我生成很多代码。

1、@Data生成Getter和Setter代码，用于类名注释

2、@Getter 生成字段对应的getXXX方法

3、@Setter生成字段对应的setXXX(xxx yyy)方法

4、@Builder构造器设计模式生成个字段的设置属性方法，该字段一般用于一些类参数可以选，可单选，可多选的环境中

5、@Slf4j使用Slf4j中门面模式，适配底层日志框架，slf4j和底层日志框架协调记录日志

6、@NoArgsConstructor生成类的默认构造函数

7、@AllArgsConstructor生成类所有字段的构造函数，常常和@Builder同时出现

8、@ToString，笔者不常用这个

9、var 兼容ECMA规范，可以编译时自动推断数类型的注解

代码如下

import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.Setter;
import lombok.ToString;
import lombok.extern.slf4j.Slf4j;
import lombok.var;

@Data
@Getter
@Setter
@Slf4j
@NoArgsConstructor
@AllArgsConstructor
@Builder
@ToString
public class LombokClass {
    @Setter
    private Integer id;

    @Setter
    @Getter
    private String name;

    public void test()
    {
        var t ="s";
    }

}

生成代码：

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class LombokClass
{
    private static final Logger log;
    private Integer id;
    private String name;

    public void test() {
        final String t = "s";
    }

    public static LombokClassBuilder builder() {
        return new LombokClassBuilder();
    }

    @Override
    public boolean equals(final Object o) {
        if (o == this) {
            return true;
        }
        if (!(o instanceof LombokClass)) {
            return false;
        }
        final LombokClass other = (LombokClass)o;
        if (!other.canEqual(this)) {
            return false;
        }
        final Object this$id = this.getId();
        final Object other$id = other.getId();
        Label_0065: {
            if (this$id == null) {
                if (other$id == null) {
                    break Label_0065;
                }
            }
            else if (this$id.equals(other$id)) {
                break Label_0065;
            }
            return false;
        }
        final Object this$name = this.getName();
        final Object other$name = other.getName();
        if (this$name == null) {
            if (other$name == null) {
                return true;
            }
        }
        else if (this$name.equals(other$name)) {
            return true;
        }
        return false;
    }

    protected boolean canEqual(final Object other) {
        return other instanceof LombokClass;
    }

    @Override
    public int hashCode() {
        final int PRIME = 59;
        int result = 1;
        final Object $id = this.getId();
        result = result * 59 + (($id == null) ? 43 : $id.hashCode());
        final Object $name = this.getName();
        result = result * 59 + (($name == null) ? 43 : $name.hashCode());
        return result;
    }

    public Integer getId() {
        return this.id;
    }

    public LombokClass() {
    }

    public LombokClass(final Integer id, final String name) {
        this.id = id;
        this.name = name;
    }

    @Override
    public String toString() {
        return "LombokClass(id=" + this.getId() + ", name=" + this.getName() + ")";
    }

    public void setId(final Integer id) {
        this.id = id;
    }

    public void setName(final String name) {
        this.name = name;
    }

    public String getName() {
        return this.name;
    }

    static {
        log = LoggerFactory.getLogger((Class)LombokClass.class);
    }

    public static class LombokClassBuilder
    {
        private Integer id;
        private String name;

        LombokClassBuilder() {
        }

        public LombokClassBuilder id(final Integer id) {
            this.id = id;
            return this;
        }

        public LombokClassBuilder name(final String name) {
            this.name = name;
            return this;
        }

        public LombokClass build() {
            return new LombokClass(this.id, this.name);
        }

        @Override
        public String toString() {
            return "LombokClass.LombokClassBuilder(id=" + this.id + ", name=" + this.name + ")";
        }
    }
}

本文要讲解的重点是@Slf4j相关的使用，使用该注解默认生成代码如下

import org.slf4j.Logger;

private static final Logger log = org.slf4j.LoggerFactory.getLogger(当前类名.class);

log有以下几个方法info,trace,debug,error,warn及对应的重载方法。

追踪了一下代码，内部会使用StringBuilder这个线程安全类处理，StringBuilder比String速度比较快，他不会创建多个String对象。

以上几个方法常用格式化代码如下（使用{}作为占位符）：

来自：https://examples.javacodegeeks.com/enterprise-java/slf4j/slf4j-format-string-example/

package com.javacodegeeks.slf4.formatting;

import java.lang.invoke.MethodHandles;
import java.text.MessageFormat;
import java.util.Calendar;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Substituting Parameters!
 *
 */
public class Slf4jSusbstitutionExample
{
    private static final Logger LOGGER = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());

    public static void main( String[] args )
    {
        String user = "john";
        String application = "gateway";

        // Crafting a message without substitution.
        // Not a good idea as the String concatenation and evaluation will happen irrespective of whether
        // logging level is permissible or not to be logged.
        LOGGER.info("Bad experience for user " + user + " at time " + Calendar.getInstance().getTime());

        // Substitution with one formatting anchor and one argument
        LOGGER.info("Bad experience for user {}", user);

        // If you happen to forget to provide a substituting object
        LOGGER.info("Bad experience for user {}");

        // Substitution with two formatting anchors and two arguments
        LOGGER.info("Bad experience for user {} at time {}", user, Calendar.getInstance().getTime());

        // Substitution with three formatting anchors and three arguments
        LOGGER.info("Bad experience for user {} at time {} while accessing {}", user, Calendar.getInstance().getTime(), application);

        // Escaping formatting anchor
        LOGGER.info("ERROR CODE \\{}; Bad experience for user {} at time {}", user, Calendar.getInstance().getTime());

        // Formatting anchor with data inside; no problem
        LOGGER.info("ERROR CODE {22}; Bad experience for user {} at time {}", user, Calendar.getInstance().getTime());

        // Crafting a message with Java's own MessageFormatter.
        // Not a good idea as per SLF4J's documentation.
        // 1. SLF4J's implementation is 10 times faster than that of MessageFormat.
        // 2. Moreover to make sure that the evaluation happens only if that particular logging
        // level is allowed, you need to do a check.
        if(LOGGER.isInfoEnabled()) {
            String message = MessageFormat.format("Bad experience for user {0} at time {1} while accessing {2}", user, Calendar.getInstance().getTime(), application);
            LOGGER.info(message);
        }
    }
}

输出结果：

2017-04-20 20:25:42 INFO  Slf4jSusbstitutionExample - Bad experience for user john at time Thu Apr 20 20:25:42 IST 2017
2017-04-20 20:25:42 INFO  Slf4jSusbstitutionExample - Bad experience for user john
2017-04-20 20:25:42 INFO  Slf4jSusbstitutionExample - Bad experience for user {}
2017-04-20 20:25:42 INFO  Slf4jSusbstitutionExample - Bad experience for user john at time Thu Apr 20 20:25:42 IST 2017
2017-04-20 20:25:42 INFO  Slf4jSusbstitutionExample - Bad experience for user john at time Thu Apr 20 20:25:42 IST 2017 while accessing gateway
2017-04-20 20:25:42 INFO  Slf4jSusbstitutionExample - ERROR CODE {}; Bad experience for user john at time Thu Apr 20 20:25:42 IST 2017
2017-04-20 20:25:42 INFO  Slf4jSusbstitutionExample - ERROR CODE {22}; Bad experience for user john at time Thu Apr 20 20:25:42 IST 2017
2017-04-20 20:25:42 INFO  Slf4jSusbstitutionExample - Bad experience for user john at time 4/20/17 8:25 PM while accessing gateway

本博客lombok其他文章:

idea中Lombok的Buider构造器模式，getter/setter正确使用方法

lombok编译时注解@Slf4j的使用及相关依赖包

Lombok子类与父类的@Builder注解冲突