Masuk di Spring Boot

1. Ikhtisar

Dalam tutorial singkat ini, kita akan menjelajahi opsi logging utama yang tersedia di Spring Boot.

Informasi lebih dalam tentang Logback tersedia di Panduan untuk Logback, sedangkan Log4j2 diperkenalkan di Pengantar Log4j2 - Penambah, Tata Letak, dan Filter.

2. Pengaturan Awal

Mari pertama-tama buat modul Spring Boot. Cara yang disarankan untuk melakukannya adalah menggunakan Spring Initializr, yang kami bahas di Tutorial Spring Boot kami.

Sekarang mari buat satu-satunya file kelas kita, LoggingController :

@RestController public class LoggingController { Logger logger = LoggerFactory.getLogger(LoggingController.class); @RequestMapping("/") public String index() { logger.trace("A TRACE Message"); logger.debug("A DEBUG Message"); logger.info("An INFO Message"); logger.warn("A WARN Message"); logger.error("An ERROR Message"); return "Howdy! Check out the Logs to see the output..."; } } 

Setelah kami memuat aplikasi web, kami akan dapat memicu baris logging tersebut hanya dengan mengunjungi // localhost: 8080 / .

3. Pencatatan Log Konfigurasi Nol

Spring Boot adalah kerangka kerja yang sangat membantu. Hal ini memungkinkan kita untuk melupakan sebagian besar pengaturan konfigurasi, banyak di antaranya disetel secara otomatis.

Dalam kasus logging, satu-satunya ketergantungan wajib adalah Apache Commons Logging.

Kita perlu mengimpornya hanya saat menggunakan Spring 4.x (Spring Boot 1.x) karena disediakan oleh modul spring-jcl Spring Framework di Spring 5 (Spring Boot 2.x).

Kita tidak perlu khawatir tentang mengimpor spring-jcl sama sekali jika kita menggunakan Spring Boot Starter (yang hampir selalu begitu). Itu karena setiap starter, seperti web spring-boot-starter-kita , bergantung pada spring-boot-starter-logging, yang sudah menarik spring-jcl untuk kita.

3.1. Pencatatan Log Balik Default

Saat menggunakan starter, Logback digunakan untuk logging secara default.

Spring Boot mengkonfigurasinya sebelumnya dengan pola dan warna ANSI untuk membuat keluaran standar lebih mudah dibaca.

Sekarang mari jalankan aplikasi dan kunjungi // localhost: 8080 / halaman, dan lihat apa yang terjadi di konsol:

Seperti yang bisa kita lihat, tingkat pencatatan default dari Logger diatur ke INFO, yang berarti bahwa pesan TRACE dan DEBUG tidak terlihat.

Untuk mengaktifkan mereka tanpa mengubah konfigurasi, kita dapat melewati debug atau -trace argumen pada baris perintah :

java -jar target/spring-boot-logging-0.0.1-SNAPSHOT.jar --trace 

3.2. Tingkat Log

Spring Boot juga memberi kita akses ke pengaturan tingkat log yang lebih terperinci melalui variabel lingkungan. Ada beberapa cara untuk melakukannya.

Pertama, kita dapat mengatur level logging kita dalam VM Options:

-Dlogging.level.org.springframework=TRACE -Dlogging.level.com.baeldung=TRACE

Alternatifnya, jika kita menggunakan Maven, kita dapat menentukan pengaturan log kita melalui baris perintah :

mvn spring-boot:run -Dspring-boot.run.arguments=--logging.level.org.springframework=TRACE,--logging.level.com.baeldung=TRACE

Saat bekerja dengan Gradle, kita bisa meneruskan pengaturan log melalui baris perintah. Ini akan membutuhkan pengaturan tugas bootRun .

Setelah selesai, kami menjalankan aplikasi:

./gradlew bootRun -Pargs=--logging.level.org.springframework=TRACE,--logging.level.com.baeldung=TRACE

Jika kita ingin mengubah verbositas secara permanen, kita dapat melakukannya di file application.properties seperti yang dijelaskan di sini:

logging.level.root=WARN logging.level.com.baeldung=TRACE 

Terakhir, kita dapat mengubah level logging secara permanen dengan menggunakan file konfigurasi framework logging kita.

Kami menyebutkan bahwa Spring Boot Starter menggunakan Logback secara default. Mari kita lihat bagaimana mendefinisikan sebuah fragmen dari file konfigurasi Logback di mana kita menyetel level untuk dua paket terpisah:

Ingatlah bahwa jika level log untuk sebuah paket ditentukan beberapa kali menggunakan opsi berbeda yang disebutkan di atas, tetapi dengan level log berbeda, level terendah yang akan digunakan.

Jadi, jika kita menyetel level logging menggunakan Logback, Spring Boot, dan variabel lingkungan secara bersamaan, level log akan menjadi TRACE , karena ini adalah yang terendah di antara level yang diminta.

4. Pembuatan Log Konfigurasi Logback

Meskipun konfigurasi default berguna (misalnya, untuk memulai dalam waktu nol selama POC atau eksperimen cepat), kemungkinan besar itu tidak cukup untuk kebutuhan sehari-hari kita.

Mari kita lihat cara menyertakan konfigurasi Logback dengan warna dan pola logging yang berbeda, dengan spesifikasi terpisah untuk konsol dan keluaran file , dan dengan kebijakan bergulir yang layak untuk menghindari pembuatan file log yang besar.

Pertama, kita harus menemukan solusi yang memungkinkan untuk menangani pengaturan pencatatan kita sendiri dan bukan mencemari properti aplikasi, yang biasanya digunakan untuk banyak pengaturan aplikasi lainnya.

Ketika file di classpath memiliki salah satu dari nama berikut, Spring Boot akan secara otomatis memuatnya di atas konfigurasi default:

  • logback-spring.xml
  • logback.xml
  • logback-spring.groovy
  • logback.groovy

Spring recommends using the -spring variant over the plain ones whenever possible, as described here.

Let's write a simple logback-spring.xml:

      %black(%d{ISO8601}) %highlight(%-5level) [%blue(%t)] %yellow(%C{1.}): %msg%n%throwable     ${LOGS}/spring-boot-logger.log  %d %p %C{1.} [%t] %m%n    ${LOGS}/archived/spring-boot-logger-%d{yyyy-MM-dd}.%i.log   10MB               

And when we run the application, here's the output:

As we can see, it now logs TRACE and DEBUG messages, and the overall console pattern is both textually and chromatically different than before.

It also now logs on a file in a /logs folder created under the current path and archives it through a rolling policy.

5. Log4j2 Configuration Logging

While Apache Commons Logging is at the core, and Logback is the reference implementation provided, all the routings to the other logging libraries are already included to make it easy to switch to them.

In order to use any logging library other than Logback, though, we need to exclude it from our dependencies.

For every starter like this one (it's the only one in our example, but we could have many of them):

 org.springframework.boot spring-boot-starter-web  

we need to turn it into a skinny version, and (only once) add our alternative library, here through a starter itself:

 org.springframework.boot spring-boot-starter-web   org.springframework.boot spring-boot-starter-logging     org.springframework.boot spring-boot-starter-log4j2  

At this point, we need to place in the classpath a file named one of the following:

  • log4j2-spring.xml
  • log4j2.xml

We'll print through Log4j2 (over SLF4J) without further modifications.

Let's write a simple log4j2-spring.xml:

        %d %p %C{1.} [%t] %m%n                    

And when we run the application, here's the output:

As we can see, the output is quite different from the Logback one — a proof that we're fully using Log4j2 now.

In addition to the XML configuration, Log4j2 allows us to use also a YAML or JSON configuration, described here.

6. Log4j2 Without SLF4J

We can also use Log4j2 natively, without passing through SLF4J.

In order to do that, we simply use the native classes:

import org.apache.logging.log4j.Logger; import org.apache.logging.log4j.LogManager; // [...] Logger logger = LogManager.getLogger(LoggingController.class); 

We don't need to perform any other modification to the standard Log4j2 Spring Boot configuration.

We can now exploit the brand-new features of Log4j2 without getting stuck with the old SLF4J interface. But we're also tied to this implementation, and we'll need to rewrite our code when switching to another logging framework.

7. Logging With Lombok

In the examples we've seen so far, we've had to declare an instance of a logger from our logging framework.

This boilerplate code can be annoying. We can avoid it using various annotations introduced by Lombok.

We'll first need to add the Lombok dependency in our build script to work with it:

 org.projectlombok lombok 1.18.4 provided 

7.1. @Slf4j and @CommonsLog

SLF4J and Apache Commons Logging APIs allow us the flexibility to change our logging framework with no impact on our code.

And we can use Lombok's @Slf4j and @CommonsLog annotations to add the right logger instance into our class: org.slf4j.Logger for SLF4J and org.apache.commons.logging.Log for Apache Commons Logging.

To see these annotations in action, let's create a class similar to LoggingController but without a logger instance. We name it as LombokLoggingController and annotate it with @Slf4j:

@RestController @Slf4j public class LombokLoggingController { @RequestMapping("/lombok") public String index() { log.trace("A TRACE Message"); log.debug("A DEBUG Message"); log.info("An INFO Message"); log.warn("A WARN Message"); log.error("An ERROR Message"); return "Howdy! Check out the Logs to see the output..."; } }

Note that we've adjusted the snippet just a bit, using log as our logger instance. This is because adding the annotation @Slf4j automatically adds a field named log.

With Zero-Configuration Logging, the application will use underlying logging implementation Logback for logging. Similarly, Log4j2 implementation is used for logging with Log4j2-Configuration Logging.

We get the same behavior when we replace the annotation @Slf4j with @CommonsLog.

7.2. @Log4j2

We can use the annotation @Log4j2 to use Log4j2 directly. So, we make a simple change to LombokLoggingController to use @Log4j2 instead of @Slf4j or @CommonsLog:

@RestController @Log4j2 public class LombokLoggingController { @RequestMapping("/lombok") public String index() { log.trace("A TRACE Message"); log.debug("A DEBUG Message"); log.info("An INFO Message"); log.warn("A WARN Message"); log.error("An ERROR Message"); return "Howdy! Check out the Logs to see the output..."; } } 

Other than logging, there are other annotations from Lombok that help in keeping our code clean and tidy. More information about them is available in Introduction to Project Lombok, and we also have a tutorial on Setting Up Lombok With Eclipse and IntelliJ.

8. Beware of Java Util Logging

Spring Boot also supports JDK logging, through the logging.properties configuration file.

There are cases when it's not a good idea to use it, though. From the documentation:

There are known classloading issues with Java Util Logging that cause problems when running from an ‘executable jar'. We recommend that you avoid it when running from an ‘executable jar' if at all possible.

It's also a good practice when using Spring 4 to manually exclude commons-logging in pom.xml, to avoid potential clashes between the logging libraries. Spring 5 instead handles it automatically, so we don't need to do anything when using Spring Boot 2.

9. JANSI on Windows

While Unix-based operating systems such as Linux and Mac OS X support ANSI color codes by default, on a Windows console, everything will be sadly monochromatic.

Windows can obtain ANSI colors through a library called JANSI.

We should pay attention to the possible class loading drawbacks, though.

We must import and explicitly activate it in the configuration as follows:

Logback:

  true  [%thread] %highlight(%-5level) %cyan(%logger{15}) - %msg %n     

Log4j2:

ANSI escape sequences are supported natively on many platforms but are not by default on Windows. To enable ANSI support, add the Jansi jar to our application and set property log4j.skipJansi to false. This allows Log4j to use Jansi to add ANSI escape codes when writing to the console.

Note: Prior to Log4j 2.10, Jansi was enabled by default. The fact that Jansi requires native code means that Jansi can only be loaded by a single class loader. For web applications, this means the Jansi jar has to be in the web container's classpath. To avoid causing problems for web applications, Log4j no longer automatically tries to load Jansi without explicit configuration from Log4j 2.10 onward.

It's also worth noting:

  • The layout documentation page contains useful Log4j2 JANSI informations in the highlight{pattern}{style} section.
  • While JANSI can color the output, Spring Boot's Banner (native or customized through the banner.txt file) will stay monochromatic.

10. Conclusion

Kami telah melihat cara utama untuk berinteraksi dengan framework logging utama dari dalam proyek Spring Boot.

Kami juga mempelajari keuntungan dan kelemahan utama dari setiap solusi.

Seperti biasa, kode sumber lengkap tersedia di GitHub.