一个简单的NoSQL内存数据库—Berkeley DB基本操作的例子

package webspider.berkeleydb; import java.io.Serializable; /** * 定义一个序列化的java类，放到Berkeley DB中 * * @author typ * */ public class Bean implements Serializable { private static final long serialVersionUID = -6865837107626208563L; private Integer id; private String name; public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } }

package webspider.berkeleydb; /** * 定义需要实现的功能接口 * * @author typ * */ public interface Frontier { /** * 获得下一条记录 * * @return * @throws Exception */ public Bean getNext() throws Exception; /** * 添加一条记录 * * @param bean * @return * @throws Exception */ public boolean putNext(Bean bean) throws Exception; }

package webspider.berkeleydb; import java.io.File; import com.sleepycat.bind.serial.StoredClassCatalog; import com.sleepycat.je.Database; import com.sleepycat.je.DatabaseConfig; import com.sleepycat.je.Environment; import com.sleepycat.je.EnvironmentConfig; /** * 封装Berkeley DB的操作 * * @author typ * */ public abstract class AbstractFrontier { private Environment env; private static final String CLASS_CATALOG = "java_class_catalog"; protected StoredClassCatalog javaCatalog; protected Database catalogDatabase; protected Database database; /** * 初始化数据库需要的各种变量 * * @param homeDirectory * @throws Exception */ public AbstractFrontier(String homeDirectory) throws Exception { EnvironmentConfig envConfig = new EnvironmentConfig(); // 设置事务处理开启， envConfig.setTransactional(true); // AllowCreate属性表示没有数据库的前提下，可以自动创建数据库 envConfig.setAllowCreate(true); // 定义Environment变量，homeDirectory指的是数据库存放路径 env = new Environment(new File(homeDirectory), envConfig); // 设置数据库的属性 DatabaseConfig dbConfig = new DatabaseConfig(); dbConfig.setTransactional(true); dbConfig.setAllowCreate(true); // 通常java对象和java对象之间的映射关系要分开存放，放置到不同的数据库中 // 存放java对象的数据库 catalogDatabase = env.openDatabase(null, CLASS_CATALOG, dbConfig); javaCatalog = new StoredClassCatalog(catalogDatabase); // 存放key/value映射的数据库<String,JavaBean> database = env.openDatabase(null, "String_JavaBean", dbConfig); } /** * 关闭数据库时候，关闭各种链接 * * @throws Exception */ public void close() throws Exception { database.close(); javaCatalog.close(); env.close(); } /** * Berkeley DB的存储键值对操作 * * @param key * @param value */ protected abstract void put(Object key, Object value); /** * Berkeley DB的得到键值对操作 * * @param key * @return */ protected abstract Object get(Object key); /** * Berkeley DB的删除键值对操作 * * @param key * @return */ protected abstract Object delete(Object key); }

package webspider.berkeleydb; import java.util.Map.Entry; import java.util.Set; import com.sleepycat.bind.EntryBinding; import com.sleepycat.bind.serial.SerialBinding; import com.sleepycat.collections.StoredMap; /** * 具体实现类 * * @author typ * */ public class BDBFrontier extends AbstractFrontier implements Frontier { // 建立map，存储key/value键值对 private StoredMap pendingUrisDBMap; /** * 初始化java对象数据库和对象映射数据库 * * @param homeDirectory * @throws Exception */ public BDBFrontier(String homeDirectory) throws Exception { super(homeDirectory); // 定义key和value的Entry EntryBinding keyBinding = new SerialBinding(javaCatalog, String.class); EntryBinding valueBinding = new SerialBinding(javaCatalog, Bean.class); // map存放在database中，database存放key/value映射 pendingUrisDBMap = new StoredMap(database, keyBinding, valueBinding, true); } /* * (non-Javadoc) * * @see webspider.berkeleydb.Frontier#getNext() */ public Bean getNext() throws Exception { Bean bean = null; if (!pendingUrisDBMap.isEmpty()) { Set<Entry<String, Bean>> entrys = pendingUrisDBMap.entrySet(); Entry<String, Bean> entry = (Entry<String, Bean>) pendingUrisDBMap .entrySet().iterator().next(); bean = entry.getValue(); delete(entry.getKey()); } return bean; } /* (non-Javadoc) * @see webspider.berkeleydb.Frontier#putNext(webspider.berkeleydb.Bean) */ public boolean putNext(Bean bean) throws Exception { put(bean.getName(), bean); return true; } /* * (non-Javadoc) * * @see webspider.berkeleydb.AbstractFrontier#put(java.lang.Object, * java.lang.Object) */ protected void put(Object key, Object value) { pendingUrisDBMap.put(key, value); } /* * (non-Javadoc) * * @see webspider.berkeleydb.AbstractFrontier#get(java.lang.Object) */ protected Object get(Object key) { return pendingUrisDBMap.get(key); } /* * (non-Javadoc) * * @see webspider.berkeleydb.AbstractFrontier#delete(java.lang.Object) */ protected Object delete(Object key) { return pendingUrisDBMap.remove(key); } /** * 测试效果，可以看到在f:\bdb文件夹下面生成了.jdb和.lck等Berkeley DB相关文件，数据存储在.jdb中 * 控制台输出刚刚插入的数据bean的Name值LiMing */ public static void main(String[] args) { try { BDBFrontier frontier = new BDBFrontier("f:\\bdb"); Bean bean = new Bean(); bean.setName("LiMing"); frontier.putNext(bean); System.out.println(frontier.getNext().getName()); frontier.close(); } catch (Exception e) { e.printStackTrace(); } } } 从上述过程看来，Berkeley DB可以很好的实现key/value这种存储方式，而且完全是通过一系列直接访问数据库的函数，而不是像关系数据库那样需要数据库连接、SQL解析等步骤。完全跟java程序中操作HashMap没有太大的区别，比较容易上手。