问题描述

在使用Azure Event Hub的SDK时候，常规情况下，发现示例代码中并没有SDK内部的日志输出。因为在Java项目中，没有添加 SLF4J 依赖，已致于在启动时候有如下提示：

SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.

那么，有什么方便的办法，能把SDK中，内部处理Event Hub的日志打印出来，并且保存在日志文件中呢？

问题解答

是的，如提示所说，使用 SLF4J 就可以了。因为Azure Event Hub SDK中使用 (com.azure.core.util.logging.ClientLogger) 对日志进行输出，所以在最外层(应用代码级)就需要有一个接收日志的Provider，那就是SLF4J。

下面的步骤，就是展示如何添加SLF4J依赖，如何添加输出到文件，输出到Console的配置，最后查看输出结果。

前提要求：根据官方示例代码，已经成功运行消费端应用：https://docs.azure.cn/zh-cn/event-hubs/event-hubs-java-get-started-send (文末附带本文的示例代码)

第一步：在 pom.xml 中添加 SLF4J 的3个依赖项

    <dependency>
      <groupId>org.slf4jgroupId>
      <artifactId>slf4j-apiartifactId>
      <version>1.7.25version>
  dependency>
  <dependency>
      <groupId>org.slf4jgroupId>
      <artifactId>slf4j-log4j12artifactId>
      <version>1.7.25version>
  dependency>
  <dependency>
      <groupId>log4jgroupId>
      <artifactId>log4jartifactId>
      <version>1.2.17version>
  dependency>

第二步：在 .\src\main\resources 目录中添加 log4j.properties 文件，并设置最关键的 日志输出级别，路径 和 格式

# Root logger option
log4j.rootLogger=INFO, stdout, FILE
# Direct log messages to stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1} - %m%n

# Direct log messages to file

# Define the file appender
log4j.appender.FILE=org.apache.log4j.FileAppender
# Set the name of the file
log4j.appender.FILE.File=Logs/log.out
# Set the immediate flush to true (default)
log4j.appender.FILE.ImmediateFlush=true
# Set the threshold to debug mode
log4j.appender.FILE.Threshold=debug
# Set the append to false, overwrite
log4j.appender.FILE.Append=false
# Define the layout for file appender
log4j.appender.FILE.layout=org.apache.log4j.PatternLayout
log4j.appender.FILE.layout.conversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1} - %m%n

第三步: 检查输出结果

1）实验项目的文件结构

2）pom.xml 中添加的 slf4j 依赖

3）为日志输出到文件和控制台配置属性

4）查看文件日志输出 

5）查看控制台日志输出

附录一：本文实验中的全部代码

1：POM.XML 文件内容

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0modelVersion>
  <groupId>com.examplegroupId>
  <artifactId>ConsumeMessageAbortartifactId>
  <version>1.0-SNAPSHOTversion>

  <name>ConsumeMessageAbortname>
  
  <url>http://www.example.comurl>

  <properties>
    <project.build.sourceEncoding>UTF-8project.build.sourceEncoding>
    <maven.compiler.source>1.8maven.compiler.source>
    <maven.compiler.target>1.8maven.compiler.target>
  properties>

  <dependencies>
    <dependency>
      <groupId>com.azuregroupId>
      <artifactId>azure-messaging-eventhubsartifactId>
      <version>5.12.2version>
    dependency>
    <dependency>
      <groupId>com.azuregroupId>
      <artifactId>azure-messaging-eventhubs-checkpointstore-blobartifactId>
      <version>1.14.0version>
    dependency>
    <dependency>
      <groupId>com.azuregroupId>
      <artifactId>azure-identityartifactId>
      <version>1.5.3version>
    dependency>
    <dependency>
      <groupId>junitgroupId>
      <artifactId>junitartifactId>
      <version>4.11version>
      <scope>testscope>
    dependency>
    <dependency>
      <groupId>org.slf4jgroupId>
      <artifactId>slf4j-apiartifactId>
      <version>1.7.25version>
  dependency>
  <dependency>
      <groupId>org.slf4jgroupId>
      <artifactId>slf4j-log4j12artifactId>
      <version>1.7.25version>
  dependency>
  <dependency>
      <groupId>log4jgroupId>
      <artifactId>log4jartifactId>
      <version>1.2.17version>
  dependency>
  dependencies>

  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.pluginsgroupId>
        <artifactId>maven-assembly-pluginartifactId>
        <version>2.5.5version>
        <configuration>
          <archive>
            <manifest>
              <mainClass>com.example.AppmainClass>
            manifest>
          archive>
          <descriptorRefs>
            <descriptorRef>jar-with-dependenciesdescriptorRef>
          descriptorRefs>
        configuration>
      plugin>
    plugins>
  build>
project>

2：src\main\resources\log4j.properties 文件内容

# Root logger option
log4j.rootLogger=INFO, stdout, FILE
# Direct log messages to stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1} - %m%n

# Direct log messages to file
# Define the file appender
log4j.appender.FILE=org.apache.log4j.FileAppender
# Set the name of the file
log4j.appender.FILE.File=Logs/log.out
# Set the immediate flush to true (default)
log4j.appender.FILE.ImmediateFlush=true
# Set the threshold to debug mode
log4j.appender.FILE.Threshold=debug
# Set the append to false, overwrite
log4j.appender.FILE.Append=false
# Define the layout for file appender
log4j.appender.FILE.layout=org.apache.log4j.PatternLayout
log4j.appender.FILE.layout.conversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1} - %m%n

3：src\main\java\com\example\App.java 文件内容

package com.example;

import com.azure.messaging.eventhubs.EventData;
import com.azure.messaging.eventhubs.EventHubClientBuilder;
import com.azure.messaging.eventhubs.EventHubConsumerAsyncClient;
import com.azure.messaging.eventhubs.EventProcessorClientBuilder;

import java.io.IOException;
import java.sql.Date;
import java.time.Instant;
import java.time.temporal.TemporalUnit;
import java.util.HashMap;
import java.util.Map;
import java.util.function.Consumer;

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

/**
 * Hello world!
 *
 */
public class App {

    final static Logger logger = LoggerFactory.getLogger(App.class);
    private static final String azureEventHubConnectionString = "event hub namespace connection string";
    private static final String azureEventHubHostName = "event hub name";

    public static void main(String[] args) throws IOException {
        System.out.println("Hello World!");

        EventHubConsumerAsyncClient consumer = new EventHubClientBuilder()
                .connectionString(azureEventHubConnectionString, azureEventHubHostName)
                .consumerGroup(EventHubClientBuilder.DEFAULT_CONSUMER_GROUP_NAME)
                .buildAsyncConsumerClient();

        try {
            consumer.receive(true).subscribe(
                    event -> {
                        EventData data = event.getData();
                        String message = "SequenceNumber is" + data.getSequenceNumber().toString()
                                + " The eventData is "
                                + data.getBodyAsString();
                        System.out.println(message);
                        logger.info(message);
                    },
                    error -> logger.error("The iot hub failed to listen for messages， error is {}" + error.toString()));

        } catch (Exception e) {
            consumer = new EventHubClientBuilder()
                    .connectionString(azureEventHubConnectionString, azureEventHubHostName)
                    .consumerGroup(EventHubClientBuilder.DEFAULT_CONSUMER_GROUP_NAME)
                    .buildAsyncConsumerClient();
            System.out.println("recollect consumer");
            logger.warn("recollect consumer");
        }

        System.out.println("Press enter to stop.");
        logger.info("Press enter to stop.");
        System.in.read();

        System.out.println("...End...");
    }

}

4：文件结构

参考资料

使用 Java 向/从 Azure 事件中心 (azure-messaging-eventhubs) 发送/接收事件 ： https://docs.azure.cn/zh-cn/event-hubs/event-hubs-java-get-started-send