Using LevelDB with Java and Go: Basic API Operations

Recently I started learning LevelDB and, after a brief study, have mastered its basic usage without any major obstacles.

In this article I share the basic LevelDB API usage in both Java and Go. LevelDB feels like a simplified version of Redis and works well as a local database, especially for caching. The official use case targets heavy write, light read workloads, making it suitable for performance‑test data recording. I may later build a performance‑test data collection tool based on LevelDB.

LevelDB Introduction

LevelDB is a key/value store built by Google that provides an ordered mapping from string keys to string values. Its core storage architecture is a Log‑Structured Merge (LSM) tree, a write‑optimized variant of a B‑tree, optimized for large sequential writes rather than small random writes.

Note: When using a library to operate LevelDB you do not need to install LevelDB itself; this misunderstanding cost me about an hour.

Java

Although the code is Java, it can also be used from Groovy; for readability I only share the Java usage.

Dependency

Maven:

<!-- https://mvnrepository.com/artifact/org.iq80.leveldb/leveldb -->
<dependency>
    <groupId>org.iq80.leveldb</groupId>
    <artifactId>leveldb</artifactId>
    <version>0.12</version>
</dependency>

Gradle:

// https://mvnrepository.com/artifact/org.iq80.leveldb/leveldb
implementation group: 'org.iq80.leveldb', name: 'leveldb', version: '0.12'

Basic Operations

Open a database file:

Iq80DBFactory factory = Iq80DBFactory.factory;
Options options = new Options();
DB db = factory.open(new File("fun"), options);

Add a key and value:

db.put(bytes("scores"), bytes("scoreJSON.toString())"));

The org.iq80.leveldb.impl.Iq80DBFactory#bytes method is used here, but you can wrap it yourself if you prefer.

Get the value of a key:

byte[] scores = db.get(bytes("scores"));

The returned value is also a byte array and needs to be converted to the target object.

Delete a key:

db.delete(bytes("fun"));

Iterate over the database:

DBIterator iterator = db.iterator();
while (iterator.hasNext()) {
    Map.Entry
next = iterator.next();
    output(next.getKey());
}

Close the database:

db.close();

After closing, you will see a directory named fun containing a set of files with extensions such as *.sst as well as files like CURRENT, LOCK, etc.

Go

Dependency

github.com/syndtr/goleveldb v1.0.0

Basic Operations

Open a database file:

db, err := leveldb.OpenFile("funtester", nil)
if err != nil {
    log.Println("creation error!", err)
}

Add a key and value:

db.Put([]byte(task.FunTester), fun, nil)

It is recommended to wrap this in a helper method.

Get the value of a key:

get, er := db.Get([]byte(task.FunTester), nil)

The returned value is also a byte array and must be transformed into the desired object.

Delete a key:

db.Delete([]byte("test"), nil)

Iterate over the database:

iterator := db.NewIterator(nil, nil)
for iterator.Next() {
    key := iterator.Key()
    value := iterator.Value()
    log.Printf("data key:%s, value:%s", key, value)
}

Close the database:

db.Close()

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