feat: java example

Author: matoous

.github/workflows/java.yaml

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+name: Java CI
+
+on:
+  push:
+    branches: [main]
+    paths: [backend/java/**, .github/workflows/java.yaml]
+  pull_request:
+    branches: [main]
+    paths: [backend/java/**, .github/workflows/java.yaml]
+
+jobs:
+  backend-java:
+    name: Backend Java
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: backend/java
+    steps:
+      - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
+
+      - name: Set up Java
+        uses: actions/setup-java@f2beeb24e141e01a676f977032f5a29d81c9e27e # v4.4.0
+        with:
+          distribution: temurin
+          java-version: '17'
+          cache: gradle
+
+      - name: Lint
+        run: ./gradlew --no-daemon spotlessCheck
+
+      - name: Build
+        run: ./gradlew --no-daemon build

backend/java/.env.example

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+SUMUP_API_KEY=
+SUMUP_MERCHANT_CODE=
+PORT=3004

backend/java/.gitignore

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+.gradle/
+build/
+
+# IDEs
+.idea/
+*.iml
+*.ipr
+*.iws
+.vscode/
+.project
+.classpath
+.settings/
+nbproject/
+
+# OS/editor noise
+.DS_Store
+*.swp
+*.swo
+*~
+
+# Logs
+*.log
+
+# Local env
+.env
+
+# JVM output
+out/
+bin/

backend/java/README.md

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+# Java example
+
+## Setup
+
+```sh
+export SUMUP_API_KEY="your_api_key"
+export SUMUP_MERCHANT_CODE="your_merchant_code"
+```
+
+## Run
+
+```sh
+gradle run
+```
+
+## Test
+
+```sh
+curl -X POST http://localhost:8080/checkouts \
+  -H "Content-Type: application/json" \
+  -d '{"amount": 10.0}'
+```

backend/java/build.gradle

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+plugins {
+    id 'application'
+    id 'com.diffplug.spotless' version '6.25.0'
+}
+
+group = 'com.sumup.examples'
+version = '1.0.0'
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    implementation 'com.sumup:sumup:0.0.5'
+    implementation 'com.fasterxml.jackson.core:jackson-databind:2.17.2'
+}
+
+application {
+    mainClass = 'com.sumup.examples.Server'
+}
+
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(17)
+    }
+}
+
+spotless {
+    java {
+        target 'src/**/*.java'
+        googleJavaFormat('1.24.0')
+    }
+    format 'misc', {
+        target '*.gradle', '*.md'
+        trimTrailingWhitespace()
+        endWithNewline()
+    }
+}

backend/java/gradle.properties

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+# Force Gradle to use JDK 17 for tools like Spotless.
+org.gradle.java.home=/Library/Java/JavaVirtualMachines/jdk-17.jdk/Contents/Home

backend/java/gradle/wrapper/gradle-wrapper.jar

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+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.2.1-bin.zip
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists