make jooq use my db connection pool

src/main/java/com/mykola2312/mptv/Main.java

@@ -45,11 +45,19 @@ public class Main {
         }
 
         if (config.db == null) {
-            logger.fatal("no database configuration. exiting.");
+            logger.fatal("no database configuration. shutting down.");
+            System.exit(1);
+            return;
+        }
+        
+        try {
+            DB.setupFromConfig(config.db);
+        } catch (RuntimeException e) {
+            logger.fatal("setupFromConfig", e);
+            logger.fatal("failed to initialize database. shutting down");
             System.exit(1);
             return;
         }
-        DB.setupFromConfig(config.db);
 
         MainFrame frame = new MainFrame();
         frame.create(config.frame);
@@ -62,16 +70,12 @@ public class Main {
         );
         flyway.migrate();
 
-        try (Connection conn = DB.getConnection()) {
-            DSLContext create = DSL.using(conn, SQLDialect.SQLITE);
-            Result<Record> result = create.select().from(TEST).fetch();
-            for (Record r : result) {
-                Integer id = r.getValue(TEST.ID);
-                String value = r.getValue(TEST.VALUE);
-                System.out.printf("%d: %s\n", id, value);
-            }
-        } catch (Exception e) {
-            e.printStackTrace();
+        DSLContext create = DSL.using(DB.CONFIG);
+        Result<Record> result = create.select().from(TEST).fetch();
+        for (Record r : result) {
+            Integer id = r.getValue(TEST.ID);
+            String value = r.getValue(TEST.VALUE);
+            System.out.printf("%d: %s\n", id, value);
         }
 
         logger.info("mptv started");

src/main/java/com/mykola2312/mptv/db/DB.java

@@ -4,6 +4,10 @@ import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.SQLException;
 
+import org.jooq.Configuration;
+import org.jooq.SQLDialect;
+import org.jooq.impl.DefaultConfiguration;
+
 import com.mykola2312.mptv.config.DBConfig;
 
 public class DB {
@@ -11,10 +15,18 @@ public class DB {
     public static String USER = "";
     public static String PASSWORD = "";
 
-    public static void setupFromConfig(DBConfig config) {
+    public static DBPool POOL;
+    public static Configuration CONFIG;
+
+    public static void setupFromConfig(DBConfig config) throws RuntimeException {
         URL = config.url;
         USER = config.user;
         PASSWORD = config.password;
+
+        POOL = new DBPool(URL);
+        CONFIG = new DefaultConfiguration()
+            .set(POOL)
+            .set(SQLDialect.SQLITE);
     }
 
     public static Connection getConnection() throws SQLException {

src/main/java/com/mykola2312/mptv/db/DBPool.java

@@ -1,9 +1,12 @@
 package com.mykola2312.mptv.db;
 
+import org.apache.log4j.Logger;
 import org.checkerframework.checker.nullness.qual.*;
 import java.sql.Connection;
+import java.sql.DriverManager;
 import java.sql.SQLException;
 import java.util.LinkedList;
+import java.util.NoSuchElementException;
 
 import org.jooq.ConnectionProvider;
 import org.jooq.exception.DataAccessException;
@@ -11,32 +14,82 @@ import org.jooq.exception.DataAccessException;
 // I can't believe that in 2024 I have to do it myself
 public class DBPool implements ConnectionProvider {
     private String url;
-    private String user;
-    private String password;
 
-    public static final int POOL_LIMIT = 4;
-    private LinkedList<Connection> connections;
+    private static final Logger logger = Logger.getLogger(DBPool.class);
 
-    public DBPool(String url, String user, String password) {
+    public static final int POOL_LOW_CAP = 4;
+
+    private class DBConnection {
+        public final Connection connection;
+        public boolean beingUsed;
+
+        public DBConnection(Connection connection, boolean beingUsed) {
+            this.connection = connection;
+            this.beingUsed = beingUsed;
+        }
+    }
+    private LinkedList<DBConnection> connections = new LinkedList<DBConnection>();
+
+    public DBPool(String url) throws RuntimeException {
         this.url = url;
-        this.user = user;
-        this.password = password;
-        
-        connections = new LinkedList<Connection>();
+
+        // allocate pool now
+        try {
+            for (int i = 0; i < POOL_LOW_CAP; i++) {
+                spawnConnection();
+            }
+        } catch (SQLException e) {
+            throw new RuntimeException("failed to allocate pool", e);
+        }
     }
 
-    protected Connection spawnConnection() throws SQLException {
-        return null;
+    protected DBConnection spawnConnection() throws SQLException {
+        DBConnection conn = new DBConnection(DriverManager.getConnection(url), false);
+        connections.add(conn);
+
+        logger.debug(String.format("spawned connection %s", conn.toString()));
+        return conn;
     }
 
     @Override
     public @Nullable Connection acquire() throws DataAccessException {
-        throw new UnsupportedOperationException("Unimplemented method 'acquire'");
+        DBConnection conn;
+        try {
+            conn = connections
+                .stream()
+                .filter(db -> !db.beingUsed)
+                .findFirst()
+                .get();
+        } catch (NoSuchElementException e) {
+            try {
+                conn = spawnConnection();
+            } catch (SQLException e1) {
+                throw new DataAccessException("failed to spawn connection", e1);
+            }
+        }
+
+        conn.beingUsed = true;
+
+        logger.debug(String.format("allocated connection %s", conn.toString()));
+        return conn.connection;
     }
 
     @Override
-    public void release(Connection arg0) throws DataAccessException {
-        throw new UnsupportedOperationException("Unimplemented method 'release'");
+    public void release(Connection conn) throws DataAccessException {
+        try {
+            DBConnection db = connections
+                .stream()
+                .filter(dbConn -> conn == dbConn.connection)
+                .findFirst()
+                .get();
+            
+            db.beingUsed = false;
+            if (connections.size() > POOL_LOW_CAP) {
+                connections.remove(db);
+            }
+        } catch (NoSuchElementException e) {
+            throw new DataAccessException("connection is not present in pool");
+        }
     }
     
 }

src/main/resources/log4j.properties

@@ -1,8 +1,9 @@
-log4j.rootLogger=INFO, file, stdout
+log4j.rootLogger=DEBUG, file, stdout
 
 # log_out
 log4j.appender.file=org.apache.log4j.RollingFileAppender
 log4j.appender.file.File=log/log_out.log
+log4j.appender.File.Threshold=INFO
 log4j.appender.file.MaxFileSize=1024KB
 log4j.appender.file.MaxBackupIndex=2
 log4j.appender.file.layout=org.apache.log4j.PatternLayout
@@ -10,6 +11,7 @@ log4j.appender.file.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:
 
 # stdout
 log4j.appender.stdout=org.apache.log4j.ConsoleAppender
+log4j.appender.stdout.Threshold=DEBUG
 log4j.appender.stdout.Target=System.out
 log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
 log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n