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How to get a handle on SpringBoot log files

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Release: 2023-05-12 11:46:05
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    SpringBoot log file

    1. What is the use of logs

    The log is an important part of the program. Imagine if the program reports an error and does not allow you to open the console to view the log, can you find the cause of the error?

    For us, the main purpose of logs is to troubleshoot and locate problems. In addition to discovering and locating problems, we can also achieve the following functions through logs:

    • Record user login logs to facilitate analysis of whether the user logs in normally or maliciously cracks the user

    • Record the operation log of the system to facilitate data recovery and locate the operator

    • Record the execution time of the program to facilitate future optimization programs to provide data support

    2. How to use logs

    The Spring Boot project will have log output by default when it is started, as shown below:

    How to get a handle on SpringBoot log files

    Through the above information we can find:

    • Spring Boot has a built-in logging framework

    • By default, the output log is not defined by the developer and printing, so how do developers define print logs in the program?

    • The log is printed on the console by default, but the console log cannot be saved. How to save the log permanently?

    3. Customized log printing

    Implementation steps for developers to customize log printing:

    • Get it in the program Log

    • Use the relevant syntax of the log object to output the content to be printed

    3.1 Get the log object in the program
    private static final Logger log = LoggerFactory.getLogger(UserController.class);
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    The log factory needs to pass the type of each class in, so that we can know the ownership class of the log, and locate the problem more conveniently and intuitively

    Note: The logger object belongs to the org.slf4j package, do not import it Wrong

    How to get a handle on SpringBoot log files

    3.2 Use the log object to print the log

    There are many ways to print the log object. We can use the info method to output the log,

    @Controller
    @ResponseBody
    public class UserController {
        private static final Logger log = LoggerFactory.getLogger(UserController.class);
        @RequestMapping("/sayhi")
        public void sayHi() {
            log.trace("trace");
            log.debug("debug");
            log.info("info");
            log.warn("warn");
            log.error("error");
        }
    }
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    How to get a handle on SpringBoot log files

    4. Log level

    4.1 What is the use of log level?
    • The log level can help you filter out important information. For example, if you set the log level to error, you can only see the error log of the program. For ordinary debugging logs and business logs It can be ignored. This saves developers time in screening

    • The log level can control whether a program needs to print logs in different environments. For example, in the development environment we need very detailed information, and in the production environment in order to maintain performance and security will output a small amount of logs, and such requirements can be achieved through log levels

    4.2 Classification and use of log levels

    Log levels are divided into:

    • trace: trace, meaning a little, the lowest level

    • debug: print key information when debugging is required

    • info: Ordinary print information (default log level)

    • warn: Warning: Does not affect use, but needs attention

    • error: error message, higher level error log message

    • fatal: fatal, an event that causes the program to exit execution due to code exception

    The order of log levels:

    How to get a handle on SpringBoot log files

    The higher up, the less information is received. If warn is set, only warn and the levels above it can be received.

    Log level settings

    logging:
      level:
        root: error
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    Default log output level

    Clear the log settings in the configuration file and observe the console output The log level

    comes to the conclusion that the default log output level is info

    When there are local log level and global log level settings, then when accessing the local log, the local log is used level. That is, the priority of local logs is higher than the priority of global logs

    5. Log persistence

    The above logs are output on the console, but in the production environment we need Save the log so that you can trace the problem after a problem occurs. The process of saving the log is called persistence

    If you want to persist the date, you only need to specify the storage directory of the log in the configuration file or specify the log. Save the file name, Spring Boot will write the console log to the corresponding directory or file

    Configure the saving path of the log file:

    logging:
      file:
        path: D:\rizhi
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    The saved path, which contains escape characters For aspect settings, we can use this / as a separator.

    If you insist on using the delimiter under Windows, we need to use the \ escape character to escape

    配置日志文件的文件名:

    logging:
      file:
        name: D:/rizhi/logger/spring.log
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    6. 更简单的日志输出–lombok

    每次使用LoggerFactory.getLogger很繁琐,且每个类都添加一遍,也很麻烦。这里的lombok是一种更好的日志输出方式

    • 添加lombok框架支持

    • 使用@slf4j注解输出日志

    6.1 添加 lombok 依赖

    首先要安装一个插件:

    How to get a handle on SpringBoot log files

    然后再pom.xml页面右键、

    How to get a handle on SpringBoot log files

    How to get a handle on SpringBoot log files

    How to get a handle on SpringBoot log files

    最后重新添加依赖就可以了

    How to get a handle on SpringBoot log files

    6.2 输出日志

    使用@Slf4j注解,在程序中使用log对象即可输入日志并且只能使用log对象才能输出,这是lombok提供的对象名

    6.3 lombok原理解释

    lombok 能够打印⽇志的密码就在 target ⽬录⾥⾯,target 为项⽬最终执⾏的代码,查看 target ⽬录我们可以发现:

    How to get a handle on SpringBoot log files

    这里的@Slf4j注解变成了一个对象。

    下面是java程序的运行原理:

    How to get a handle on SpringBoot log files

    6.4 lombok更多注解说明

    基本注解

    注解 作用
    @Getter 自动添加get方法
    @Setter 自动添加set方法
    @ToString 自动添加toString方法
    @EqualsAndHashCode 自动添加equals和hasCode方法
    @NoArgsConstructor 自动添加无参构造方法
    @AllArgsConstructor 自动添加全属性构造方法,顺序按照属性的定义顺序
    @NonNull 属性不能为null
    @RequiredArgsConstructor 自动添加必须属性的构造方法,final + @NonNull的属性为需

    组合注解:

    注解 作用
    @Data @Getter+@Setter+EqualsAndHashCode+@RequiredArgsConstructor+@NoArgsConstructor

    日志注解

    注解 作用
    @Slf4j 添加一个名为log的对象

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