JDBC driver (Java)¶

DecentDB ships an in-tree Java stack under bindings/java/:

• bindings/java/driver/ — JDBC driver (com.decentdb.jdbc.DecentDBDriver)
• bindings/java/native/ — JNI bridge (libdecentdb_jni.*)
• bindings/java/dbeaver-extension/ — DBeaver packaging
• tests/bindings/java/Smoke.java — low-level FFM smoke for the raw C ABI

The JDBC driver targets the stable DecentDB C ABI through JNI. Public behavior should match the engine and C ABI, rather than inventing Java-only semantics.

Supported JDBC URLs¶

The driver accepts URLs of the form:

jdbc:decentdb:/absolute/path/to/db.ddb
jdbc:decentdb:/absolute/path/to/db.ddb?mode=open
jdbc:decentdb:/absolute/path/to/db.ddb?readOnly=true

Supported connection properties:

• mode — openOrCreate (default), open, or create
• readOnly — true or false (default false)

Currently unsupported at open time:

• busyTimeoutMs
• cachePages

The stable C ABI currently exposes only default create, open, and open_or_create entry points. The Java driver therefore rejects busyTimeoutMs and cachePages instead of silently pretending they work.

Build locally¶

From the repository root:

cargo build -p decentdb --release
cd bindings/java
./gradlew :driver:jar

This builds the core shared library, the JNI bridge, and the JDBC jar. The jar embeds the matching native libraries for the current OS/arch from target/release/.

Validate the Java binding¶

The Java build itself targets Java 17 bytecode. In this repository, the Gradle test path is currently validated with JDK 21:

export JAVA_HOME=/usr/lib/jvm/java-21-openjdk
export PATH="$JAVA_HOME/bin:$PATH"
cd bindings/java
./gradlew :driver:test

Run the standalone JDBC example¶

The driver now includes a runnable CRUD example that covers schema creation, prepared statements, DECIMAL, BOOL, TIMESTAMP, rollback, metadata, and basic error handling:

export JAVA_HOME=/usr/lib/jvm/java-21-openjdk
export PATH="$JAVA_HOME/bin:$PATH"
cd bindings/java
./gradlew :driver:runCrudExample

To target a specific database path:

./gradlew :driver:runCrudExample -PexampleArgs="/absolute/path/to/example.ddb"

Run the benchmark¶

From bindings/java/:

export JAVA_HOME=/usr/lib/jvm/java-21-openjdk
export PATH="$JAVA_HOME/bin:$PATH"
./gradlew :driver:benchmarkFetch -PbenchmarkArgs="--count 100000 --point-reads 5000 --fetchmany-batch 1024 --db-prefix java_bench_fetch"

Supported benchmark options:

• --engine <all|decentdb|sqlite>
• --count <n>
• --point-reads <n>
• --fetchmany-batch <n>
• --point-seed <n>
• --db-prefix <prefix>
• --sqlite-jdbc <jar_path>
• --keep-db

When --engine all is used, the benchmark will try to auto-discover a local sqlite-jdbc jar from common DBeaver, Rider, and Maven cache locations. You can also pass it explicitly with --sqlite-jdbc.

Run the low-level FFM smoke¶

tests/bindings/java/Smoke.java validates the raw C ABI independently of the JDBC driver. With JDK 21, this path uses the preview Foreign Function & Memory API:

export JAVA_HOME=/usr/lib/jvm/java-21-openjdk
export PATH="$JAVA_HOME/bin:$PATH"
cargo build -p decentdb
javac --enable-preview --release 21 tests/bindings/java/Smoke.java
java --enable-preview --enable-native-access=ALL-UNNAMED -cp tests/bindings/java Smoke

The smoke test auto-detects target/debug/ or target/release/ for the core shared library.

JDBC usage example¶

import com.decentdb.jdbc.DecentDBConnection;
import com.decentdb.jdbc.DecentDBDataSource;

import java.math.BigDecimal;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.Timestamp;
import java.time.Instant;

DecentDBDataSource dataSource = new DecentDBDataSource("jdbc:decentdb:/tmp/shop.ddb");
dataSource.setMode("openOrCreate");

try (Connection connection = dataSource.getConnection()) {
    connection.setAutoCommit(false);

    try (PreparedStatement create = connection.prepareStatement(
        "CREATE TABLE IF NOT EXISTS products (" +
            "id INT64 PRIMARY KEY, " +
            "name TEXT NOT NULL, " +
            "price DECIMAL(12,2) NOT NULL, " +
            "active BOOL NOT NULL, " +
            "updated_at TIMESTAMP)"
    )) {
        create.executeUpdate();
    }

    try (PreparedStatement insert = connection.prepareStatement(
        "INSERT INTO products (id, name, price, active, updated_at) VALUES ($1, $2, $3, $4, $5)"
    )) {
        insert.setLong(1, 1L);
        insert.setString(2, "Keyboard");
        insert.setBigDecimal(3, new BigDecimal("129.99"));
        insert.setBoolean(4, true);
        insert.setTimestamp(5, Timestamp.from(Instant.now()));
        insert.executeUpdate();
    }

    connection.commit();

    try (PreparedStatement query = connection.prepareStatement(
        "SELECT id, name, price FROM products WHERE id = $1"
    )) {
        query.setLong(1, 1L);
        try (ResultSet rs = query.executeQuery()) {
            while (rs.next()) {
                System.out.println(rs.getString("name") + " => " + rs.getBigDecimal("price"));
            }
        }
    }

    if (connection instanceof DecentDBConnection decent) {
        System.out.println("Engine version: " + decent.getEngineVersion());
        decent.checkpoint();
    }
}

DecentDB's Java driver currently follows the engine's native positional placeholder style ($1, $2, ...) in prepared SQL.

DecentDB-specific connection helpers¶

DecentDBConnection adds a small number of engine-truth helpers beyond the standard JDBC Connection surface:

• isInTransaction() — queries the engine via ddb_db_in_transaction
• getAbiVersion() — exposes ddb_abi_version
• getEngineVersion() — exposes ddb_version
• checkpoint() — runs ddb_db_checkpoint
• saveAs(path) — runs ddb_db_save_as

saveAs(path) requires a destination path that does not already exist.

Thread-safety and pooling¶

DecentDB uses a single-process, one-writer / many-readers model.

• Connection methods are serialized internally per connection
• Statement, PreparedStatement, and ResultSet are not thread-safe
• DecentDBDataSource is a thin configuration wrapper, not a pooling implementation

If you place DecentDB behind an external pool, keep write-heavy workloads at a maximum size of 1.

Metadata and framework support¶

The driver includes:

• a DataSource implementation: com.decentdb.jdbc.DecentDBDataSource
• JDBC metadata for tables, columns, indexes, keys, and type mapping
• DecentDB-specific schema helpers on DecentDBDatabaseMetaData for table DDL and trigger listing

For DBeaver integration details, see the DBeaver guide.