What is Gradle Wrapper? How to generate and use it? - 面试题

Gradle Wrapper is an important feature of Gradle that allows projects to be built with a specific version of Gradle without requiring Gradle to be pre-installed on developers' machines. Here's a detailed explanation of Gradle Wrapper:

Gradle Wrapper Introduction

Gradle Wrapper is a script and a set of JAR files used to download and run a specific version of Gradle. It ensures that all developers and CI/CD systems use the same version of Gradle for builds.

Wrapper File Structure

shell
project/
├── gradle/
│   └── wrapper/
│       ├── gradle-wrapper.jar
│       └── gradle-wrapper.properties
├── gradlew
├── gradlew.bat
└── build.gradle

File Description

gradlew: Executable script on Unix/Linux/macOS
gradlew.bat: Batch script on Windows
gradle/wrapper/gradle-wrapper.jar: Wrapper JAR file
gradle/wrapper/gradle-wrapper.properties: Wrapper configuration file

Generating Wrapper

Generate Using Gradle Command

bash
# Generate Wrapper (using current Gradle version)
gradle wrapper

# Specify Gradle version
gradle wrapper --gradle-version 8.0

# Use release version
gradle wrapper --gradle-distribution-url https://services.gradle.org/distributions/gradle-8.0-bin.zip

Configure in build.gradle

groovy
// build.gradle
wrapper {
    gradleVersion = '8.0'
    distributionType = Wrapper.DistributionType.BIN
    distributionPath = wrapperPath
    archivePath = wrapperPath
}

Wrapper Configuration

gradle-wrapper.properties

properties
# Gradle distribution download URL
distributionUrl=https\://services.gradle.org/distributions/gradle-8.0-bin.zip

# Distribution base URL (optional)
distributionBase=GRADLE_USER_HOME

# Distribution path (optional)
distributionPath=wrapper/dists

# Zip cache base URL (optional)
zipStoreBase=GRADLE_USER_HOME

# Zip cache path (optional)
zipStorePath=wrapper/dists

Distribution Types

Gradle Wrapper provides three distribution types:

bin: Contains only binary files, small size, fast download

properties
distributionUrl=https\://services.gradle.org/distributions/gradle-8.0-bin.zip

all: Contains binary files and source code, larger size, suitable for viewing source code
```
properties
distributionUrl=https\://services.gradle.org/distributions/gradle-8.0-all.zip
```

only: Contains only source code (rarely used)

properties
distributionUrl=https\://services.gradle.org/distributions/gradle-8.0-src.zip

Using Wrapper

Basic Usage

bash
# Execute Gradle tasks using Wrapper
./gradlew build

# On Windows
gradlew.bat build

# View available tasks
./gradlew tasks

# Clean project
./gradlew clean

Specify JVM Options

bash
# Set JVM memory
./gradlew build -Dorg.gradle.jvmargs="-Xmx2048m -XX:MaxMetaspaceSize=512m"

# Use specific Java version
JAVA_HOME=/path/to/java17 ./gradlew build

Pass Project Properties

bash
# Pass project properties
./gradlew build -Pprofile=production

# Pass system properties
./gradlew build -Dspring.profiles.active=production

Customizing Wrapper

Custom Distribution Location

groovy
// build.gradle
wrapper {
    gradleVersion = '8.0'
    distributionType = Wrapper.DistributionType.BIN
    
    // Use custom repository
    distributionUrl = 'https://my-company.com/gradle/gradle-8.0-bin.zip'
}

Use Local Gradle Distribution

groovy
// gradle-wrapper.properties
distributionUrl=file\:///path/to/local/gradle-8.0-bin.zip

Configure Network Proxy

bash
# Set proxy
./gradlew build -Dhttp.proxyHost=proxy.example.com -Dhttp.proxyPort=8080

# Configure in gradle.properties
# gradle.properties
systemProp.http.proxyHost=proxy.example.com
systemProp.http.proxyPort=8080
systemProp.https.proxyHost=proxy.example.com
systemProp.https.proxyPort=8080

Version Management

Update Wrapper Version

bash
# Update to latest version
./gradlew wrapper --gradle-version=8.1

# Update to specific version
./gradlew wrapper --gradle-version=8.0.2

# Update to release candidate version
./gradlew wrapper --gradle-version=8.2-rc-1

Check Current Version

bash
# View Gradle version used by Wrapper
./gradlew --version

# View Wrapper configuration
cat gradle/wrapper/gradle-wrapper.properties

Best Practices

1. Commit Wrapper Files to Version Control

bash
# Commit these files to Git
git add gradlew gradlew.bat
git add gradle/wrapper/gradle-wrapper.jar
git add gradle/wrapper/gradle-wrapper.properties

# Don't commit downloaded Gradle distributions
echo "gradle/wrapper/dists/" >> .gitignore

2. Use Fixed Version

groovy
// build.gradle
wrapper {
    gradleVersion = '8.0'  // Use fixed version
    distributionType = Wrapper.DistributionType.BIN
}

3. Use Wrapper in CI/CD

yaml
# GitHub Actions example
- name: Build with Gradle
  run: ./gradlew build

# Jenkins Pipeline example
sh './gradlew build'

# GitLab CI example
script:
  - ./gradlew build

4. Optimize Download Speed

groovy
// Use domestic mirror
wrapper {
    gradleVersion = '8.0'
    distributionUrl = 'https://mirrors.cloud.tencent.com/gradle/gradle-8.0-bin.zip'
}

Troubleshooting

1. Wrapper Script Has No Execute Permission

bash
# Add execute permission
chmod +x gradlew

2. Download Failed

bash
# Manually download Gradle distribution
wget https://services.gradle.org/distributions/gradle-8.0-bin.zip

# Place in correct directory
mkdir -p ~/.gradle/wrapper/dists/gradle-8.0-bin
cp gradle-8.0-bin.zip ~/.gradle/wrapper/dists/gradle-8.0-bin/

3. Version Conflict

bash
# Clear local cache
rm -rf ~/.gradle/wrapper/dists/

# Re-download
./gradlew build

4. Network Issues

bash
# Use offline mode
./gradlew build --offline

# Configure proxy
./gradlew build -Dhttp.proxyHost=proxy.example.com -Dhttp.proxyPort=8080

Security Considerations

1. Verify Wrapper JAR

bash
# Verify Wrapper JAR checksum
shasum gradle/wrapper/gradle-wrapper.jar

2. Use HTTPS

properties
# gradle-wrapper.properties
distributionUrl=https\://services.gradle.org/distributions/gradle-8.0-bin.zip

3. Restrict Network Access

groovy
// In enterprise environments, restrict Wrapper to only download from internal repositories
wrapper {
    distributionUrl = 'https://internal-repo.example.com/gradle/gradle-8.0-bin.zip'
}

Advanced Usage

1. Wrapper in Multi-Project

bash
# Generate Wrapper in root project
./gradlew wrapper

# All subprojects can use the same Wrapper
./gradlew :module1:build
./gradlew :module2:build

2. Custom Wrapper Script

bash
# Modify gradlew script to add custom logic
# For example: set environment variables, check Java version, etc.

3. Use Gradle Version Catalog

groovy
// gradle/libs.versions.toml
[versions]
gradle = "8.0"

// Use in build.gradle
wrapper {
    gradleVersion = libs.versions.gradle.get()
}