add CLAUDE.md for AI-assisted development

Documents build commands, architecture, and implementation details to help
Claude Code instances understand the codebase structure and data flow.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+jrunner is a Java CLI tool for migrating data between databases. It reads data from a source database using SQL queries and writes it to a destination table, batching inserts for performance. The tool supports multiple database types via JDBC drivers including PostgreSQL, IBM AS/400, and Microsoft SQL Server.
+
+## Build and Test Commands
+
+Build the project:
+```bash
+gradle build
+# or use wrapper
+./gradlew build
+```
+
+Run tests:
+```bash
+gradle test
+# or use wrapper
+./gradlew test
+```
+
+Build distribution package:
+```bash
+gradle build
+# Creates app/build/distributions/app.zip
+```
+
+Deploy to /opt (as documented in readme.md):
+```bash
+sudo cp app/build/distributions/app.zip /opt/
+sudo rm -rf /opt/app/
+sudo unzip /opt/app.zip -d /opt/
+sudo rm /opt/app.zip
+sudo chown ptrowbridge:ptrowbridge -R /opt/app/
+```
+
+## Architecture
+
+### Single-File Design
+The entire application logic resides in `app/src/main/java/jrunner/jrunner.java`. This is a monolithic command-line tool with no abstraction layers or separate modules.
+
+### Data Flow
+1. Parse command-line arguments (-scu, -scn, -scp for source; -dcu, -dcn, -dcp for destination)
+2. Read SQL query from file specified by -sq flag
+3. Connect to source and destination databases via JDBC
+4. Execute source query and fetch results (fetch size: 10,000 rows)
+5. Build batched INSERT statements (250 rows per batch)
+6. Execute batches against destination table specified by -dt flag
+7. Optionally clear target table before insert if -c flag is set
+
+### Type Handling
+The tool includes explicit handling for different SQL data types in a switch statement (lines 229-312). Supported types include VARCHAR, TEXT, CHAR, CLOB, DATE, TIME, TIMESTAMP, and BIGINT. String types get quote escaping and optional trimming.
+
+### Database Drivers
+JDBC drivers are configured in `app/build.gradle`:
+- PostgreSQL: org.postgresql:postgresql:42.5.0
+- IBM AS/400 (JT400): net.sf.jt400:jt400:11.0
+- Microsoft SQL Server: com.microsoft.sqlserver:mssql-jdbc:9.2.0.jre8
+- SQL Server Integrated Auth: com.microsoft.sqlserver:mssql-jdbc_auth:9.2.0.x64
+
+The AS/400 driver requires explicit Class.forName() registration (line 144).
+
+## Configuration
+
+The project uses a YAML configuration format (run.yml) to specify database connections, SQL script paths, and runtime options. However, the main application currently uses command-line arguments instead of parsing this YAML file.
+
+Command-line flags:
+- `-scu` - source JDBC URL
+- `-scn` - source username
+- `-scp` - source password
+- `-dcu` - destination JDBC URL
+- `-dcn` - destination username
+- `-dcp` - destination password
+- `-sq` - path to source SQL query file
+- `-dt` - fully qualified destination table name
+- `-t` - trim text fields (default: true)
+- `-c` - clear target table before insert (default: true)
+
+## Key Implementation Details
+
+### Batch Size
+INSERT statements are batched at 250 rows (hardcoded at line 324). When the batch threshold is reached, sql is prepended with "INSERT INTO {table} VALUES" and executed.
+
+### Error Handling
+SQLException handling prints stack trace and exits immediately with System.exit(0). There is no transaction rollback or partial failure recovery.
+
+### Performance Considerations
+- Result set fetch size is set to 10,000 rows (line 173)
+- Progress counter prints with carriage return for real-time updates
+- Timestamps captured at start (line 174) and end (line 368) for duration tracking