pg-index-health is an embeddable Java library and schema linter for PostgreSQL that detects common database anti-patterns and promotes best practices. It provides over 40 diagnostic checks covering duplicated/intersected indexes, bloat, missing indexes, inappropriate column types, naming violations, unlogged tables, sequence overflow, and many more. The library is designed for integration into applications (via Spring Boot starter) or use in CI pipelines to enforce schema quality. It supports both single-host and high-availability PostgreSQL clusters, with checks that can run statically (against schema only) or require accumulated statistics. The architecture is a multi-module Gradle project: `pg-index-health-model` defines immutable domain objects (Table, Index, Column, ForeignKey, etc.) with validation and composable predicates; `pg-index-health-core` implements host-level checks using a template pattern (`AbstractCheckOnHost`) with SQL queries loaded from a separate submodule; `pg-index-health` wraps these into cluster-level checks (`AbstractCheckOnCluster`) that aggregate results across primary and standby nodes; `pg-index-health-jdbc-connection` provides connection factories with primary host detection and multi-host URL parsing; `pg-index-health-generator` produces corrective SQL migrations; `pg-index-health-logger` formats results; and `pg-index-health-testing` offers Testcontainers-based test fixtures. Optional Jackson 2/3 modules enable JSON serialization of results. Key entry points include `StandardChecksOnHost` and `StandardChecksOnCluster` which enumerate all available checks, and the Spring Boot auto-configuration (`DatabaseStructureHealthAutoConfiguration`) that registers check beans. Data flows involve querying PostgreSQL system catalogs (`pg_catalog`, `pg_stat_*`), mapping result sets to domain objects via `ResultSetExtractor` implementations, applying exclusion predicates (e.g., skip Flyway/Liquibase tables, small tables, named objects), and returning lists of deviations. External dependencies are minimal: PostgreSQL JDBC driver, Apache DBCP2 connection pool, and Testcontainers for testing. The library is published to Maven Central and includes a BOM for dependency management.
Alibaba Druid is a production-grade Java library providing a high-performance JDBC connection pool, a multi-dialect SQL parser, an SQL injection firewall, and built-in monitoring/statistics. In production, it replaces or augments standard connection pools (HikariCP, DBCP) with advanced features like connection leak detection, PSCache, and web console monitoring. The SQL parser supports 30+ dialects (MySQL, PostgreSQL, Oracle, Hive, ClickHouse, etc.) and is used for SQL formatting, parameterization, and analysis. The WallFilter provides configurable security rules to block SQL injection and dangerous operations. The library integrates deeply with Spring Boot via dedicated starters for Boot 2/3/4, and exposes metrics through JMX. Architecture is organized around a filter chain pattern for intercepting JDBC calls, a visitor pattern for AST manipulation, and an SPI-based provider system for firewall rules.
WxJava is a comprehensive Java SDK for the WeChat ecosystem, providing client libraries for Official Accounts (MP), Mini Programs (MiniApp), Enterprise WeChat (CP), WeChat Pay, Open Platform, Video Channels, and more. It is designed as a multi-module library to be embedded in Java applications, with first-class support for Spring Boot and Solon frameworks via auto-configuration starters. The SDK abstracts HTTP client backends (Apache, OkHttp, Jodd, HttpComponents), provides Redis-based config storage for distributed token management, and implements multi-tenant patterns for managing multiple WeChat accounts. It handles the full lifecycle of WeChat API integration: request signing, serialization (Gson/Jackson/XStream), message routing, and callback verification. The codebase is large and well-structured, though it shows signs of duplication across modules and mixed serialization frameworks, reflecting organic growth over time.
Arthas is a production-grade Java diagnostic and monitoring agent developed by Alibaba. It attaches to running JVMs without code changes or restarts, enabling real-time inspection of threads, memory, classes, method invocations, and system properties through an interactive shell (telnet/HTTP/WebSocket) or programmatic APIs. The architecture consists of a core agent (bytecode instrumentation via ASM/ByteKit), a command framework with over 40 built-in commands (watch, trace, stack, dashboard, profiler, etc.), multiple transport protocols (telnet, HTTP, gRPC, MCP for AI integration), and a tunnel server for remote connectivity. It also includes experimental modules for JFR analysis, cluster management, and gRPC-web proxies. Key external dependencies include Netty, OGNL, CFR decompiler, and async-profiler.