Eclipse-Slf4j 的配置与使用

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1. 安装 lombok

方法参加  https://projectlombok.org/setup/eclipse

2. 错误处理

lombok 安装后，在Java代码中是 @Slj4j 注解时编译通过，运行时抛错

错误Failed to load class org.slf4j.impl.StaticLoggerBinder

下面信息是官方给出的解决方案 https://www.slf4j.org/codes.html

Failed to load class org.slf4j.impl.StaticLoggerBinder

This warning message is reported when the org.slf4j.impl.StaticLoggerBinder class could not be loaded into memory. This happens when no appropriate SLF4J binding could be found on the class path. Placing one (and only one) of slf4j-nop.jar slf4j-simple.jar, slf4j-log4j12.jar, slf4j-jdk14.jar or logback-classic.jar on the class path should solve the problem.

SINCE 1.6.0 As of SLF4J version 1.6, in the absence of a binding, SLF4J will default to a no-operation (NOP) logger implementation.

If you are responsible for packaging an application and do not care about logging, then placing slf4j-nop.jar on the class path of your application will get rid of this warning message. Note that embedded components such as libraries or frameworks should not declare a dependency on any SLF4J binding but only depend on slf4j-api. When a library declares a compile-time dependency on a SLF4J binding, it imposes that binding on the end-user, thus negating SLF4J’s purpose.

解决办法：pom文件中加入 slf4j-log4j12 的引用，特别注意 Scope, 默认是 test，可以删除 scope

修改后运行 java 项目，出现下列警告，但是控制台不能正常输出信息。

log4j:WARN No appenders could be found for logger.
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.

解决方案

A. 修改 pom 文件里的引用，删除 slf4j-log4j12 引用，加入 log4j-slf4j-impl 和 log4j-core 引用。

<!-- https://mvnrepository.com/artifact/org.projectlombok/lombok -->
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.2</version>
    <scope>provided</scope>
</dependency>

<!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-api -->
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.7.25</version>
</dependency>

<!-- https://mvnrepository.com/artifact/org.apache.logging.log4j/log4j-slf4j-impl -->
<dependency>
  <groupId>org.apache.logging.log4j</groupId>
  <artifactId>log4j-slf4j-impl</artifactId>
  <version>2.1</version>
</dependency>

<!-- https://mvnrepository.com/artifact/org.apache.logging.log4j/log4j-core -->
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-core</artifactId>
    <version>2.1</version>
</dependency>

</dependencies>

B. 在 src 目录下创建 resources 目录，并创建 log4j2.xml 文件，文件内容如下 

<?xml version="1.0" encoding="UTF-8"?>

<configuration status="info">

<appenders>
    <console name="Console" target="SYSTEM_OUT">
        <PatternLayout pattern="[%d{HH:mm:ss:SSS}] [%p] - %l - %m%n"/>
    </console>

    <RollingFile name="RollingFileInfo" fileName="${sys:user.home}/logs/hpaasvc/info.log"
                 filePattern="${sys:user.home}/logs/hpaasvc/$${date:yyyy-MM}/info-%d{yyyy-MM-dd}-%i.log">
        <Filters>
            <ThresholdFilter level="INFO"/>
            <ThresholdFilter level="WARN" onMatch="DENY" onMismatch="NEUTRAL"/>
        </Filters>
        <PatternLayout pattern="[%d{HH:mm:ss:SSS}] [%p] - %l - %m%n"/>
        <Policies>
            <TimeBasedTriggeringPolicy/>
            <SizeBasedTriggeringPolicy size="100 MB"/>
        </Policies>
    </RollingFile>

    <RollingFile name="RollingFileWarn" fileName="${sys:user.home}/logs/hpaasvc/warn.log"
                 filePattern="${sys:user.home}/logs/hpaasvc/$${date:yyyy-MM}/warn-%d{yyyy-MM-dd}-%i.log">
        <Filters>
            <ThresholdFilter level="WARN"/>
            <ThresholdFilter level="ERROR" onMatch="DENY" onMismatch="NEUTRAL"/>
        </Filters>
        <PatternLayout pattern="[%d{HH:mm:ss:SSS}] [%p] - %l - %m%n"/>
        <Policies>
            <TimeBasedTriggeringPolicy/>
            <SizeBasedTriggeringPolicy size="100 MB"/>
        </Policies>
    </RollingFile>

    <RollingFile name="RollingFileError" fileName="${sys:user.home}/logs/hpaasvc/error.log"
                 filePattern="${sys:user.home}/logs/hpaasvc/$${date:yyyy-MM}/error-%d{yyyy-MM-dd}-%i.log">
        <ThresholdFilter level="ERROR"/>
        <PatternLayout pattern="[%d{HH:mm:ss:SSS}] [%p] - %l - %m%n"/>
        <Policies>
            <TimeBasedTriggeringPolicy/>
            <SizeBasedTriggeringPolicy size="100 MB"/>
        </Policies>
    </RollingFile>

</appenders>

<loggers>
    <!--过滤掉spring和hibernate的一些无用的debug信息-->
    <logger name="org.springframework" level="INFO">
    </logger>
    <logger name="org.hibernate" level="INFO">
    </logger>
    <root level="all">
        <appender-ref ref="Console"/>
        <appender-ref ref="RollingFileInfo"/>
        <appender-ref ref="RollingFileWarn"/>
        <appender-ref ref="RollingFileError"/>
    </root>
</loggers>

</configuration>

C. 把 resources 目录加入 Java build Path