Java Patch Workflow

Creating Unified Diff Patches

# Create a patch from changes to a specific file
diff -u original_file.java modified_file.java > my_fix.patch

# Create patch with context lines
diff -u -p original.java modified.java > fix.patch

# Apply a patch
patch -p1 < fix.patch           # Strip 1 prefix component
patch -p0 < fix.patch           # Don't strip (exact path match)
patch --dry-run -p1 < fix.patch # Test without applying

Git-Based Patching

# Create patch from staged changes
git diff HEAD > my_fix.patch

# Create patch from specific commit
git format-patch HEAD~1

# Apply git format-patch
git am patch_file.patch

# Apply unified diff
git apply patch_file.patch
git apply --check patch_file.patch  # Dry run

Apache Druid Build

Full Build (skip web-console for OOM prevention)

cd /root/druid
mvn clean package -DskipTests \
  -Dcheckstyle.skip=true -Dpmd.skip=true \
  -Dforbiddenapis.skip=true -Dspotbugs.skip=true \
  -Danimal.sniffer.skip=true -Denforcer.skip=true \
  -Djacoco.skip=true -Ddependency-check.skip=true \
  -pl '!web-console' -pl indexing-service -am

Module-Specific Build

# Build only the indexing-service and dependencies
mvn package -DskipTests -pl indexing-service -am

# Build specific module with quality checks skipped
mvn package -DskipTests -Dcheckstyle.skip=true -pl processing

Patch File Organization

/root/patches/
├── 01-fix-javascript-injection.patch     # Primary root cause fix
├── 02-fix-sampler-validation.patch       # Defense in depth
└── README.md                            # Fix description

Common Issues

Patch Offset Errors

If patch reports "offset" or "fuzz", the patch may be for a different file version. Use patch --fuzz=3 to allow more context flexibility.

Build Failures After Patch

• Check for compilation errors: mvn compile first
• Verify imports are added for new classes used
• Check Guice injection: ensure @Inject annotation is present for DI

Finding the Right JAR After Build

find /root/druid -name "druid-indexing-service-*.jar" -not -path "*/test*"
# Typically at: druid/indexing-service/target/druid-indexing-service-*.jar