Spring PetClinic Application

Introduce the PetClinic application which is a Java application that will be used as the test bed for this workshop.

Tags:

5 minute read

For this exercise, we will use the Spring PetClinic application. This is a very popular sample java application built with Spring framework (Spring Boot).

Get Started

To get started, clone the PetClinic repository starting from our home directory:
```
cd $HOME 
git clone https://github.com/spring-projects/spring-petclinic
```
Change into the spring-petclinic directory:
```
cd spring-petclinic
```

Start a MySQL database for Pet Clinic to use:

docker run -d -e MYSQL_USER=petclinic -e MYSQL_PASSWORD=petclinic -e MYSQL_ROOT_PASSWORD=root -e MYSQL_DATABASE=petclinic -p 3306:3306 docker.io/mysql:5.7.8

Next, run the maven command to compile/build/package Pet Clinic:
```
./mvnw package -Dmaven.test.skip=true
```
Note
This will take a few minutes the first time you run, maven will download a lot of dependencies before it actually compiles the app. Future executions will be a lot shorter.
Once the compilation is complete, you can run the application with the following command:
```
java -jar target/spring-petclinic-*.jar --spring.profiles.active=mysql
```
You can verify that the application is running by visiting http://localhost:8080. Click around, generate errors, add visits, etc.

Enable Structured Logging

The PetClinic app is built using standard Log4j formatted log entries. These log entries, while easily human readable, are much more difficult to machine parse due to inconsistencies in the log format. It’s easy enough to switch from human-readable logs to structured logs in JSON format.

Edit pom.xml and insert the following highlighted list of dependencies at the end of the <dependencies>...</dependencies> section (around line 108-109):

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   <dependency>
     <groupId>org.springframework.boot</groupId>
     <artifactId>spring-boot-devtools</artifactId>
     <optional>true</optional>
   </dependency>

   <!-- logback -->
   <dependency>
     <groupId>ch.qos.logback.contrib</groupId>
     <artifactId>logback-json-classic</artifactId>
     <version>0.1.5</version>
   </dependency>

   <dependency>
     <groupId>ch.qos.logback.contrib</groupId>
     <artifactId>logback-jackson</artifactId>
     <version>0.1.5</version>
   </dependency>

   <dependency>
     <groupId>com.fasterxml.jackson.core</groupId>
     <artifactId>jackson-databind</artifactId>
     <version>2.14.0-rc1</version>
   </dependency>

   <dependency>
     <groupId>com.fasterxml.jackson.core</groupId>
     <artifactId>jackson-core</artifactId>
     <version>2.13.4</version>
   </dependency>
   <!-- end of logback -->
 </dependencies>

A git diff will look like this:

git diff

diff --git a/pom.xml b/pom.xml
index d29355c..eeec4dc 100644
--- a/pom.xml
+++ b/pom.xml
@@ -106,6 +106,32 @@
       <artifactId>spring-boot-devtools</artifactId>
       <optional>true</optional>
     </dependency>
+
+    <!-- logback -->
+    <dependency>
+      <groupId>ch.qos.logback.contrib</groupId>
+      <artifactId>logback-json-classic</artifactId>
+      <version>0.1.5</version>
+    </dependency>
+
+    <dependency>
+      <groupId>ch.qos.logback.contrib</groupId>
+      <artifactId>logback-jackson</artifactId>
+      <version>0.1.5</version>
+    </dependency>
+
+    <dependency>
+      <groupId>com.fasterxml.jackson.core</groupId>
+      <artifactId>jackson-databind</artifactId>
+      <version>2.14.0-rc1</version>
+    </dependency>
+
+    <dependency>
+      <groupId>com.fasterxml.jackson.core</groupId>
+      <artifactId>jackson-core</artifactId>
+      <version>2.13.4</version>
+    </dependency>
+    <!-- end of logback -->
   </dependencies>

   <build>

The structured logging uses the Logback framework, so let’s configure it to output as we need. Create a new file src/main/resources/logback.xml and set the contents as:

<?xml version="1.0" encoding="UTF-8"?>
<configuration scan="true">
    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>%date{MMM dd HH:mm:ss} %-5level petclinic[1]: %msg %n</pattern>
        </encoder>
    </appender>

    <appender name="FileLogger" class="ch.qos.logback.core.FileAppender">
        <file>/tmp/petclinic.json</file>
        <append>false</append>
        <immediateFlush>true</immediateFlush>

        <layout class="ch.qos.logback.contrib.json.classic.JsonLayout">
            <jsonFormatter class="ch.qos.logback.contrib.jackson.JacksonJsonFormatter">
                <prettyPrint>false</prettyPrint>
            </jsonFormatter>
            <timestampFormat>yyyy-MM-dd' 'HH:mm:ss</timestampFormat>
            <appendLineSeparator>true</appendLineSeparator>
        </layout>
    </appender>

    <root level="DEBUG">
        <appender-ref ref="FileLogger"/>
        <appender-ref ref="STDOUT"/>
    </root>
</configuration>

We can now repackage the PetClinic application with:
```
./mvnw package -Dmaven.test.skip=true
```

Rerun the application with the following command:

java -jar target/spring-petclinic-*.jar --spring.profiles.active=mysql

After initialization, the remaining output should be JSON format:

           |\      _,,,--,,_
          /,`.-'`'   ._  \-;;,_
_______ __|,4-  ) )_   .;.(__`'-'__     ___ __    _ ___ _______
|       | '---''(_/._)-'(_\_)   |   |   |   |  |  | |   |       |
|    _  |    ___|_     _|       |   |   |   |   |_| |   |       | __ _ _
|   |_| |   |___  |   | |       |   |   |   |       |   |       | \ \ \ \
|    ___|    ___| |   | |      _|   |___|   |  _    |   |      _|  \ \ \ \
|   |   |   |___  |   | |     |_|       |   | | |   |   |     |_    ) ) ) )
|___|   |_______| |___| |_______|_______|___|_|  |__|___|_______|  / / / /
==================================================================/_/_/_/

:: Built with Spring Boot :: 2.7.3

2022-11-08 16:33:41.664  INFO 12708 --- [           main] o.s.s.petclinic.PetClinicApplication     : Starting PetClinicApplication v2.7.3 using Java 14.0.2 on mbp1 with PID 12708 (/Users/bmeyer/spring-petclinic/target/spring-petclinic-2.7.3.jar started by bmeyer in /Users/bmeyer/spring-petclinic)
2022-11-08 16:33:41.670  INFO 12708 --- [           main] o.s.s.petclinic.PetClinicApplication     : The following 1 profile is active: "mysql"
2022-11-08 16:33:44.722  INFO 12708 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data JPA repositories in DEFAULT mode.
2022-11-08 16:33:44.863  INFO 12708 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Finished Spring Data repository scanning in 122 ms. Found 2 JPA repository interfaces.
2022-11-08 16:33:46.914  INFO 12708 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2022-11-08 16:33:46.935  INFO 12708 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2022-11-08 16:33:46.935  INFO 12708 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.65]
2022-11-08 16:33:47.107  INFO 12708 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2022-11-08 16:33:47.108  INFO 12708 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 5313 ms
2022-11-08 16:33:48.447  INFO 12708 --- [           main] org.ehcache.core.EhcacheManager          : Cache 'vets' created in EhcacheManager.
2022-11-08 16:33:48.485  INFO 12708 --- [           main] org.ehcache.jsr107.Eh107CacheManager     : Registering Ehcache MBean javax.cache:type=CacheStatistics,CacheManager=urn.X-ehcache.jsr107-default-config,Cache=vets
2022-11-08 16:33:48.566  INFO 12708 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Starting...
2022-11-08 16:33:49.015  INFO 12708 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Start completed.
2022-11-08 16:33:49.404  INFO 12708 --- [           main] o.hibernate.jpa.internal.util.LogHelper  : HHH000204: Processing PersistenceUnitInfo [name: default]
2022-11-08 16:33:49.537  INFO 12708 --- [           main] org.hibernate.Version                    : HHH000412: Hibernate ORM core version 5.6.10.Final
2022-11-08 16:33:49.889  INFO 12708 --- [           main] o.hibernate.annotations.common.Version   : HCANN000001: Hibernate Commons Annotations {5.1.2.Final}
2022-11-08 16:33:50.182  INFO 12708 --- [           main] org.hibernate.dialect.Dialect            : HHH000400: Using dialect: org.hibernate.dialect.MySQL57Dialect
2022-11-08 16:33:51.781  INFO 12708 --- [           main] o.h.e.t.j.p.i.JtaPlatformInitiator       : HHH000490: Using JtaPlatform implementation: [org.hibernate.engine.transaction.jta.platform.internal.NoJtaPlatform]
2022-11-08 16:33:51.801  INFO 12708 --- [           main] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'default'
2022-11-08 16:33:54.914  INFO 12708 --- [           main] o.s.b.a.e.web.EndpointLinksResolver      : Exposing 13 endpoint(s) beneath base path '/actuator'
2022-11-08 16:33:55.032  INFO 12708 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2022-11-08 16:33:55.055  INFO 12708 --- [           main] o.s.s.petclinic.PetClinicApplication     : Started PetClinicApplication in 14.627 seconds (JVM running for 15.515)

Our Logback configuration includes an entry to write the logs to the file /tmp/petclinic.log. Verify logs are being written to it as these will be used in the next section:

more /tmp/petclinic.json

{"timestamp":"2022-11-08 16:48:10","level":"INFO","thread":"main","logger":"org.springframework.samples.petclinic.PetClinicApplication","message":"Starting PetClinicApplication v2.7.3 using Java 14.0.2 on mbp1 with PID 13883 (/Users/bmeyer/spring-petclinic/target/spring-petclinic-2.7.3.jar started by bmeyer in /Users/bmeyer/spring-petclinic)","context":"default"}
{"timestamp":"2022-11-08 16:48:10","level":"DEBUG","thread":"background-preinit","logger":"org.jboss.logging","message":"Logging Provider: org.jboss.logging.Log4j2LoggerProvider","context":"default"}
{"timestamp":"2022-11-08 16:48:10","level":"INFO","thread":"background-preinit","logger":"org.hibernate.validator.internal.util.Version","message":"HV000001: Hibernate Validator 6.2.4.Final","context":"default"}
{"timestamp":"2022-11-08 16:48:10","level":"INFO","thread":"main","logger":"org.springframework.samples.petclinic.PetClinicApplication","message":"The following 1 profile is active: \"mysql\"","context":"default"}
{"timestamp":"2022-11-08 16:48:10","level":"DEBUG","thread":"background-preinit","logger":"org.hibernate.validator.internal.xml.config.ValidationXmlParser","message":"Trying to load META-INF/validation.xml for XML based Validator configuration.","context":"default"}
...

NOTE

To ingest these logs properly, each log entry needs to appear on its own line followed by an appended line separator. We configured this in our Logback configuration with this line in the FileLogger’s layout config:

			<appendLineSeparator>true</appendLineSeparator>

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Last modified March 13, 2023: Merge pull request #58 from logdna/dependabot/npm_and_yarn/autoprefixer-10.4.14 (11f56fc)