LevelDB--键值对数据库（KVDB）

特色

键值对数据库，能够简单的看作一个只能get/put的map
写入速度比查询速度更快

demo

考虑到咱们使用的时候多半会用到字符串，因此我进行了一点多此一举的扩展git

gitee地址

https://gitee.com/ichiva/leveldb-demo.git

主要依赖

<dependency>
            <groupId>org.iq80.leveldb</groupId>
            <artifactId>leveldb</artifactId>
            <version>0.7</version>
        </dependency>
        <dependency>
            <groupId>org.iq80.leveldb</groupId>
            <artifactId>leveldb-api</artifactId>
            <version>0.7</version>
        </dependency>

编写测试用例

链接数据库

DB db  = null;

    @Before
    public void Before() throws IOException {
        DBFactory factory = new Iq80DBFactory();
        Options options = new Options();
        db  = factory.open(new File("./leveldb"), options);
    }

写入数据

@Test
    public void put(){
        db.put("二哥".getBytes(),"关羽".getBytes());
    }

获取数据

@Test
    public void get(){
        byte[] bytes = db.get("二哥".getBytes());
        System.out.println("二哥 => " + new String(bytes));
    }

遍历数据库

@Test
    public void iterator(){
        DBIterator it = db.iterator();
        while (it.hasNext()) {
            Map.Entry<byte[], byte[]> next = it.next();
            System.out.println("key = " + new String(next.getKey()));
            System.out.println("val = " + new String(next.getValue()));
        }
    }

别忘了关闭数据库

@After
    public void After() throws IOException {
        if(null != db) db.close();
    }

多此一举的来扩展一下，用于简化字符串操做

/**
 * 简化字符串操做
 */
public class StringDB extends DbImpl {
    
    public static final String CHAR_SET = "UTF-8";
    
    public StringDB(Options options, File databaseDir) throws IOException {
        super(options, databaseDir);
    }
    
    public StringDB(String dir) throws IOException {
        this(new Options(),new File(dir));
    }

    public void put(String key, String value) throws DBException {
        try {
            put(key.getBytes(CHAR_SET),value.getBytes(CHAR_SET));
        } catch (UnsupportedEncodingException e) {
            throw new RuntimeException(e);
        }
    }

    public String get(String key) throws DBException {
        try {
            return new String(get(key.getBytes(CHAR_SET)),CHAR_SET);
        } catch (UnsupportedEncodingException e) {
            throw new RuntimeException(e);
        }
    }
}

总结，leveldb用起来就像是一个硬盘版的redis，惟一不足的是没有提供key的过滤功能redis

PS.这货是谷歌的亲儿子，应该能够放心的在生成环境中使用数据库

gitee地址

https://gitee.com/ichiva/leveldb-demo.git