added chnages

Dockerfile

@@ -0,0 +1,10 @@
+FROM ubuntu:20.04 as build
+RUN apt update && \
+    apt install openjdk-17-jdk -y && \
+    apt install maven -y && \
+    apt install git -y && \
+    git clone https://github.com/spring-projects/spring-petclinic.git && \
+    cd spring-petclinic && \
+    ./mvnw package
+EXPOSE 8080
+CMD [ "java", "-jar", "/spring-petclinic/target/spring-petclinic-3.0.0-SNAPSHOT.jar" ]

Jenkinsfile

@@ -0,0 +1,22 @@
+pipeline{
+    agent{
+        label 'docker'
+    }
+    triggers{
+        pollSCM('* * * * *')
+    }
+    parameters{
+        choice(name: 'branch_name', choices: ['main', 'two', 'three'], description: 'selecting branch')
+    }
+    environment{
+        dockerhub_registry_name = "lahari104"
+        image_name = "spc" 
+    }
+    stages{
+        stage('docker image build'){
+            steps{
+                sh 'docker image build -t spc:1.0 .' 
+            }
+        }
+    }
+}