Merge 'bindings/java: Refactor to favor composition over inheritance ' from Kim Seon Woo

## Changes
- AS-IS
  - `LimboConnection` implements `Connection`
  - `JDBC4Connection` implements `LimboConnection`
- TO-BE
  - `LimboConnection` doesn't implement `Connection`. It is used to
represent connection to limbo only.
  - `JDBC4Connection` implements `Connection` directly. Holds
`LimboConnection` in member field.
- This helps remove the complexity of java's `Connection` interface away
from `LimboConnection`. We can focus on implementing limbo's feature
inside `LimboConnection` and let `JDBC4Connection` handle the
interoperability with jdbc world.
## Reference
https://github.com/tursodatabase/limbo/issues/615

Closes #916

bindings/java/README.md

@@ -4,15 +4,17 @@ The Limbo JDBC driver is a library for accessing and creating Limbo database fil
 
 ## Project Status
 
-The project is actively developed. Feel free to open issues and contribute. 
+The project is actively developed. Feel free to open issues and contribute.
 
 To view related works, visit this [issue](https://github.com/tursodatabase/limbo/issues/615).
 
-## How to use 
+## How to use
 
-Currently, we have not published to the maven central. Instead, you can locally build the jar and deploy it to maven local to use it. 
+Currently, we have not published to the maven central. Instead, you can locally build the jar and deploy it to
+maven local to use it.
+
+### Build jar and publish to maven local
 
-### Build jar and publish to maven local 
 ```shell
 $ cd bindings/java 
 
@@ -23,44 +25,16 @@ $ make macos_x86
 $ make publish_local
 ```
 
-Now you can use the dependency as follows: 
+Now you can use the dependency as follows:
+
 ```kotlin
 dependencies {
-  implementation("org.github.tursodatabase:limbo:0.0.1-SNAPSHOT") 
+    implementation("org.github.tursodatabase:limbo:0.0.1-SNAPSHOT")
 }
 ```
 
-## Development
+## Code style
 
-### How to Run Tests
-
-To run tests, use the following command:
-
-```shell
-$ make test
-``` 
-
-### Code Formatting
-
-To unify Java's formatting style, we use Spotless. To apply the formatting style, run:
-
-```shell
-$ make lint_apply
-```
-
-To apply the formatting style for Rust, run the following command:
-
-```shell 
-$ cargo fmt 
-``` 
-
-## Concepts
-
-Note that this project is actively developed, so the concepts might change in the future.
-
-- `LimboDB` represents a Limbo database.
-- `LimboConnection` represents a connection to `LimboDB`. Multiple `LimboConnections` can be created on the same
-  `LimboDB`.
-- `LimboStatement` represents a Limbo database statement. Multiple `LimboStatements` can be created on the same
-  `LimboConnection`.
-- `LimboResultSet` represents the result of `LimboStatement` execution. It is one-to-one mapped to `LimboStatement`.
+- Favor composition over inheritance. For example, `JDBC4Connection` doesn't implement `LimboConnection`. Instead,
+  it includes `LimboConnection` as a field. This approach allows us to preserve the characteristics of Limbo using
+  `LimboConnection` easily while maintaining interoperability with the Java world using `JDBC4Connection`. 

bindings/java/src/main/java/org/github/tursodatabase/JDBC.java

@@ -5,7 +5,6 @@ import java.util.Locale;
 import java.util.Properties;
 import org.github.tursodatabase.annotations.Nullable;
 import org.github.tursodatabase.annotations.SkipNullableCheck;
-import org.github.tursodatabase.core.LimboConnection;
 import org.github.tursodatabase.jdbc4.JDBC4Connection;
 import org.github.tursodatabase.utils.Logger;
 import org.github.tursodatabase.utils.LoggerFactory;
@@ -24,7 +23,7 @@ public class JDBC implements Driver {
   }
 
   @Nullable
-  public static LimboConnection createConnection(String url, Properties properties)
+  public static JDBC4Connection createConnection(String url, Properties properties)
       throws SQLException {
     if (!isValidURL(url)) return null;
 

bindings/java/src/main/java/org/github/tursodatabase/core/LimboConnection.java

@@ -2,7 +2,6 @@ package org.github.tursodatabase.core;
 
 import static org.github.tursodatabase.utils.ByteArrayUtils.stringToUtf8ByteArray;
 
-import java.sql.Connection;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.util.Properties;
@@ -11,7 +10,7 @@ import org.github.tursodatabase.utils.LimboExceptionUtils;
 import org.github.tursodatabase.utils.Logger;
 import org.github.tursodatabase.utils.LoggerFactory;
 
-public abstract class LimboConnection implements Connection {
+public class LimboConnection {
   private static final Logger logger = LoggerFactory.getLogger(LimboConnection.class);
 
   private final long connectionPtr;
@@ -38,11 +37,10 @@ public abstract class LimboConnection implements Connection {
     return LimboDBFactory.open(url, filePath, properties);
   }
 
-  protected void checkOpen() throws SQLException {
+  public void checkOpen() throws SQLException {
     if (isClosed()) throw new SQLException("database connection closed");
   }
 
-  @Override
   public void close() throws SQLException {
     if (isClosed()) {
       return;
@@ -53,7 +51,6 @@ public abstract class LimboConnection implements Connection {
 
   private native void _close(long connectionPtr);
 
-  @Override
   public boolean isClosed() throws SQLException {
     return closed;
   }
@@ -80,14 +77,7 @@ public abstract class LimboConnection implements Connection {
 
   private native long prepareUtf8(long connectionPtr, byte[] sqlUtf8) throws SQLException;
 
-  /** @return busy timeout in milliseconds. */
-  public int getBusyTimeout() {
-    // TODO: add support for busyTimeout
-    return 0;
-  }
-
   // TODO: check whether this is still valid for limbo
-
   /**
    * Checks whether the type, concurrency, and holdability settings for a {@link ResultSet} are
    * supported by the SQLite interface. Supported settings are:
@@ -102,7 +92,7 @@ public abstract class LimboConnection implements Connection {
    * @param resultSetConcurrency the concurrency setting.
    * @param resultSetHoldability the holdability setting.
    */
-  protected void checkCursor(int resultSetType, int resultSetConcurrency, int resultSetHoldability)
+  public void checkCursor(int resultSetType, int resultSetConcurrency, int resultSetHoldability)
       throws SQLException {
     if (resultSetType != ResultSet.TYPE_FORWARD_ONLY) {
       throw new SQLException("SQLite only supports TYPE_FORWARD_ONLY cursors");
@@ -115,10 +105,6 @@ public abstract class LimboConnection implements Connection {
     }
   }
 
-  public void setBusyTimeout(int busyTimeout) {
-    // TODO: add support for busy timeout
-  }
-
   /**
    * Throws formatted SQLException with error code and message.
    *

bindings/java/src/main/java/org/github/tursodatabase/jdbc4/JDBC4Connection.java

@@ -7,17 +7,24 @@ import java.util.Properties;
 import java.util.concurrent.Executor;
 import org.github.tursodatabase.annotations.SkipNullableCheck;
 import org.github.tursodatabase.core.LimboConnection;
+import org.github.tursodatabase.core.LimboStatement;
 
-public class JDBC4Connection extends LimboConnection {
+public class JDBC4Connection implements Connection {
+
+  private final LimboConnection connection;
 
   private Map<String, Class<?>> typeMap = new HashMap<>();
 
   public JDBC4Connection(String url, String filePath) throws SQLException {
-    super(url, filePath);
+    this.connection = new LimboConnection(url, filePath);
   }
 
   public JDBC4Connection(String url, String filePath, Properties properties) throws SQLException {
-    super(url, filePath, properties);
+    this.connection = new LimboConnection(url, filePath, properties);
+  }
+
+  public LimboStatement prepare(String sql) throws SQLException {
+    return connection.prepare(sql);
   }
 
   @Override
@@ -35,8 +42,8 @@ public class JDBC4Connection extends LimboConnection {
   @Override
   public Statement createStatement(
       int resultSetType, int resultSetConcurrency, int resultSetHoldability) throws SQLException {
-    checkOpen();
-    checkCursor(resultSetType, resultSetConcurrency, resultSetHoldability);
+    connection.checkOpen();
+    connection.checkCursor(resultSetType, resultSetConcurrency, resultSetHoldability);
 
     return new JDBC4Statement(this);
   }
@@ -69,12 +76,12 @@ public class JDBC4Connection extends LimboConnection {
 
   @Override
   public void close() throws SQLException {
-    super.close();
+    connection.close();
   }
 
   @Override
   public boolean isClosed() throws SQLException {
-    return super.isClosed();
+    return connection.isClosed();
   }
 
   @Override
@@ -140,13 +147,13 @@ public class JDBC4Connection extends LimboConnection {
 
   @Override
   public int getHoldability() throws SQLException {
-    checkOpen();
+    connection.checkOpen();
     return ResultSet.CLOSE_CURSORS_AT_COMMIT;
   }
 
   @Override
   public void setHoldability(int holdability) throws SQLException {
-    checkOpen();
+    connection.checkOpen();
     if (holdability != ResultSet.CLOSE_CURSORS_AT_COMMIT) {
       throw new SQLException("Limbo only supports CLOSE_CURSORS_AT_COMMIT");
     }
@@ -214,8 +221,8 @@ public class JDBC4Connection extends LimboConnection {
   public PreparedStatement prepareStatement(
       String sql, int resultSetType, int resultSetConcurrency, int resultSetHoldability)
       throws SQLException {
-    checkOpen();
-    checkCursor(resultSetType, resultSetConcurrency, resultSetHoldability);
+    connection.checkOpen();
+    connection.checkCursor(resultSetType, resultSetConcurrency, resultSetHoldability);
     return new JDBC4PreparedStatement(this, sql);
   }
 
@@ -348,4 +355,14 @@ public class JDBC4Connection extends LimboConnection {
     // TODO
     return false;
   }
+
+  public void setBusyTimeout(int busyTimeout) {
+    // TODO: add support for busy timeout
+  }
+
+  /** @return busy timeout in milliseconds. */
+  public int getBusyTimeout() {
+    // TODO: add support for busyTimeout
+    return 0;
+  }
 }

bindings/java/src/main/java/org/github/tursodatabase/jdbc4/JDBC4PreparedStatement.java

@@ -23,14 +23,13 @@ import java.sql.Time;
 import java.sql.Timestamp;
 import java.util.Calendar;
 import org.github.tursodatabase.annotations.SkipNullableCheck;
-import org.github.tursodatabase.core.LimboConnection;
 import org.github.tursodatabase.core.LimboResultSet;
 
 public class JDBC4PreparedStatement extends JDBC4Statement implements PreparedStatement {
 
   private final String sql;
 
-  public JDBC4PreparedStatement(LimboConnection connection, String sql) throws SQLException {
+  public JDBC4PreparedStatement(JDBC4Connection connection, String sql) throws SQLException {
     super(connection);
 
     this.sql = sql;

bindings/java/src/main/java/org/github/tursodatabase/jdbc4/JDBC4Statement.java

@@ -10,13 +10,12 @@ import java.sql.Statement;
 import java.util.concurrent.locks.ReentrantLock;
 import org.github.tursodatabase.annotations.Nullable;
 import org.github.tursodatabase.annotations.SkipNullableCheck;
-import org.github.tursodatabase.core.LimboConnection;
 import org.github.tursodatabase.core.LimboResultSet;
 import org.github.tursodatabase.core.LimboStatement;
 
 public class JDBC4Statement implements Statement {
 
-  private final LimboConnection connection;
+  private final JDBC4Connection connection;
   @Nullable protected LimboStatement statement = null;
 
   // Because JDBC4Statement has different life cycle in compared to LimboStatement, let's use this
@@ -34,7 +33,7 @@ public class JDBC4Statement implements Statement {
 
   private ReentrantLock connectionLock = new ReentrantLock();
 
-  public JDBC4Statement(LimboConnection connection) {
+  public JDBC4Statement(JDBC4Connection connection) {
     this(
         connection,
         ResultSet.TYPE_FORWARD_ONLY,
@@ -43,7 +42,7 @@ public class JDBC4Statement implements Statement {
   }
 
   public JDBC4Statement(
-      LimboConnection connection,
+      JDBC4Connection connection,
       int resultSetType,
       int resultSetConcurrency,
       int resultSetHoldability) {

bindings/java/src/test/java/org/github/tursodatabase/JDBCTest.java

@@ -6,21 +6,21 @@ import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.SQLException;
 import java.util.Properties;
-import org.github.tursodatabase.core.LimboConnection;
+import org.github.tursodatabase.jdbc4.JDBC4Connection;
 import org.junit.jupiter.api.Test;
 
 class JDBCTest {
 
   @Test
   void null_is_returned_when_invalid_url_is_passed() throws Exception {
-    LimboConnection connection = JDBC.createConnection("jdbc:invalid:xxx", new Properties());
+    JDBC4Connection connection = JDBC.createConnection("jdbc:invalid:xxx", new Properties());
     assertThat(connection).isNull();
   }
 
   @Test
   void non_null_connection_is_returned_when_valid_url_is_passed() throws Exception {
     String fileUrl = TestUtils.createTempFile();
-    LimboConnection connection = JDBC.createConnection("jdbc:sqlite:" + fileUrl, new Properties());
+    JDBC4Connection connection = JDBC.createConnection("jdbc:sqlite:" + fileUrl, new Properties());
     assertThat(connection).isNotNull();
   }