LevelDB使用例子

LevelDB简介

Level高效的kv数据，提供较高性能的本地存储(持久化)的功能。可为应用提供嵌入式的数据存储工作。

maven依赖

使用较常用的iq80

<dependency>
        <groupId>org.iq80.leveldb</groupId>
        <artifactId>leveldb</artifactId>
        <version>0.10</version>
</dependency>

简单操作的实现

基于spring的简单操作代码

@Slf4j
@Service
public class LevelDBTest {

    private DB db = null;

    //@Value("${levelDB.folder}")
    private String dbFolder = "db/test.db";

    private String charset = "utf-8";


    //spring启动时初始化
    @PostConstruct
    public void initLevelDB() {

        DBFactory factory = new Iq80DBFactory();
        Options options = new Options();
        options.createIfMissing(true);
        try {
            this.db = factory.open(new File(dbFolder), options);
        } catch (IOException e) {
            log.error("levelDB启动异常", e);
        }
    }

    //基于fastjson的对象序列化
    public byte[] serializer(Object obj) {
        byte[] jsonBytes = JSON.toJSONBytes(obj, new SerializerFeature[]{SerializerFeature.DisableCircularReferenceDetect});
        return jsonBytes;
    }

    //存放数据
    public void put(String key, Object val) {
        try {
            this.db.put(key.getBytes(charset), this.serializer(val));
        } catch (UnsupportedEncodingException e) {
            log.error("编码转化异常", e);
        }
    }

    //根据key获取数据
    public byte[] get(String key) {
        byte[] val = null;
        try {
            val = db.get(key.getBytes(charset));
        } catch (Exception e) {
            log.error("levelDB get error", e);
        }
        return val;
    }

    //根据key删除数据
    public void delete(String key) {
        try {
            db.delete(key.getBytes(charset));
        } catch (Exception e) {
            log.error("levelDB delete error", e);
        }

    }

    //获取所有key
    public List<String> getKeys() {

        List<String> list = new ArrayList<>();
        DBIterator iterator = null;
        try {
            iterator = db.iterator();
            while (iterator.hasNext()) {
                Map.Entry<byte[], byte[]> item = iterator.next();
                String key = new String(item.getKey(), charset);
                list.add(key);
            }
        } catch (Exception e) {
            log.error("遍历发生异常", e);
        } finally {
            if (iterator != null) {
                try {
                    iterator.close();
                } catch (IOException e) {
                    log.error("遍历发生异常", e);
                }

            }
        }
        return list;
    }

    //spring销毁对象前关闭
    @PreDestroy
    public void closeDB() {
        if (db != null) {
            try {
                db.close();
            } catch (IOException e) {
                log.error("levelDB 关闭异常", e);
            }
        }
    }

}

测试代码

@RunWith(SpringRunner.class)
@SpringBootTest
public class ApplicationTests {


    @Resource
    private LevelDBTest levelDBTest;

    @Test
    public void contextLoads() {

        for (int i = 0; i < 20; ++i) {
            Map<String,Object> m = new HashMap<>();
            m.put("id",i);
            m.put("name","test_"+i);
            m.put("time",new Date());
            levelDBTest.put("k"+i,m);
        }

        List<String> keys = levelDBTest.getKeys();

        for (int i = 0; i < 20; ++i) {
            String key = keys.get(i);
            byte[] val = levelDBTest.get(key);
            try {
                System.out.println("key:"+key+",val:"+new String(val,"utf-8"));
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }

        }

    }

}