介绍和使用Berkeley DB Java Edition（嵌入式数据库）

一、 简介 

       Berkeley DB Java Edition (JE)是一个完全用JAVA写的，它适合于管理海量的，简单的数据。 

        能够高效率的处理1到1百万条记录，制约JE数据库的往往是硬件系统,而不是JE本身。 

        多线程支持，JE使用超时的方式来处理线程间的死琐问题。 

        Database都采用简单的key/value对应的形式。 

        事务支持。 
        允许创建二级库。这样我们就可以方便的使用一级key,二级key来访问我们的数据。 

        支持RAM缓冲，这样就能减少频繁的IO操作。 

        支持日志。 

        数据备份和恢复。 

        游标支持。 

二、   获取JE 

JE下载地址： 

http://www.oracle.com/technology/software/products/berkeley-db/je/index.html 

解开包后 把JE_HOME/lib/je-<version>.jar 中的jar文件添加到你的环境变量中就可以使用je了。 

相关帮助文档可以参考 JE_HOME/docs/index.html 

源代码见JE_HOME/src/*.* 

三、     JE常见的异常 

DatabaseNotFoundException 当没有找到指定的数据库的时候会返回这个异常 

DeadlockException 线程间死锁异常 

RunRecoveryException 回收异常，当发生此异常的时候，你必须得重新打开环境变量。 

四、     关于日志文件必须了解的六项 

JE的日志文件跟其他的数据库的日志文件不太一样，跟C版的DBD也是有区别的 

        JE的日志文件只能APPEND，第一个日志文件名是 00000000.jdb，当他增长到一定大小的时候(默认是10M)，开始写第二个日志文件00000001.jdb，已此类推。 

        跟C版本有所不同，JE的数据日志和事务日志是放在一起的，而不是分开放的。 

        JE cleaner负责清扫没用到的磁盘空间，删除后，或者更新后新的记录会追加进来，而原有的记录空间就不在使用了，cleaner负责清理不用的空间。 

        清理并不是立即进行的，当你关闭你的数据库环境后，通过调用一个cleaner方法来清理。 

       清理也不是只动执行的，需要你自己手动调用cleaner 方法来定时清理的。 

        日志文件的删除仅发生在检查点之后。cleaner准备出哪些log 文件需要被删除，当检查点过后，删掉一些不在被使用的文件。每写20M的日志文件就执行一次检查点，默认下。 

JE的英文文档：http://www.oracle.com/technology/documentation/berkeley-db/je/GettingStartedGuide/index.html 

JE的中文文档（不全）：http://fesir.itpub.net/post/4728/253789 
http://fesir.itpub.net/post/4728/253789 

上面大概介绍一下，接下来是我在工作中写的一个例子（仅供参考）： 

package src.util;

import java.io.File;
import java.util.List;

import junit.framework.TestCase;
import src.com.bizjato.b2b.entity.Suppliers;

import com.sleepycat.bind.EntryBinding;
import com.sleepycat.bind.serial.SerialBinding;
import com.sleepycat.bind.serial.StoredClassCatalog;
import com.sleepycat.je.Cursor;
import com.sleepycat.je.CursorConfig;
import com.sleepycat.je.Database;
import com.sleepycat.je.DatabaseConfig;
import com.sleepycat.je.DatabaseEntry;
import com.sleepycat.je.DatabaseException;
import com.sleepycat.je.Environment;
import com.sleepycat.je.EnvironmentConfig;
import com.sleepycat.je.EnvironmentMutableConfig;
import com.sleepycat.je.LockMode;
import com.sleepycat.je.OperationStatus;

/**
 * 嵌入式数据库
 * 
 * @author zhangqinjian
 *
 */
public class Jedtion extends TestCase {

	private static final String RESOURCE = ".//src//util//importData";
	private Environment env;

	private Database db, classDB;

	private StoredClassCatalog classCatalog;
	/**
	 * 初始化，设置数据库的环境和创建数据库
	 */
	public void setUp() throws Exception {

		env = new Environment(new File(".//src//util//importData"), null);
		EnvironmentMutableConfig envMutableConfig = new EnvironmentMutableConfig();
		envMutableConfig.setTxnNoSync(true);
		env.setMutableConfig(envMutableConfig);

		DatabaseConfig dbConfig = new DatabaseConfig();
		dbConfig.setAllowCreate(true);
		db = env.openDatabase(null, "myDB", dbConfig);
		classDB = env.openDatabase(null, "classDB", dbConfig);
		classCatalog = new StoredClassCatalog(classDB);
	}
	// test: put key-value
	public void testPut(String key, Suppliers supp) throws Exception {
		EntryBinding dataBinding = new SerialBinding(classCatalog,
				Suppliers.class);
		DatabaseEntry keyEntry = new DatabaseEntry(key.getBytes("UTF-8"));
		DatabaseEntry dataEntry = new DatabaseEntry();
		dataBinding.objectToEntry(supp, dataEntry);
		db.put(null, keyEntry, dataEntry);
	}
	// test: get
	public void testGet() throws Exception {
		EnvironmentConfig envConfig = new EnvironmentConfig();
		envConfig.setAllowCreate(true);
		// envConfig.setReadOnly(true);
		env = new Environment(new File(".//src//util//importData"), envConfig);
		List myDbNames = env.getDatabaseNames();
		System.out.println("Database size: " + myDbNames.size());
		for (int i = 0; i < myDbNames.size(); i++) {
			System.out.println("Database Name: " + (String) myDbNames.get(i));
		}

		DatabaseConfig dbConfig = new DatabaseConfig();
		dbConfig.setAllowCreate(true);
		// dbConfig.setReadOnly(true);
		db = env.openDatabase(null, "myDB", dbConfig);
		classDB = env.openDatabase(null, "classDB", dbConfig);
		classCatalog = new StoredClassCatalog(classDB);

		System.out.println("Db: " + db.count());

		EntryBinding dataBinding = new SerialBinding(classCatalog,
				Suppliers.class);

		DatabaseEntry keyEntry = new DatabaseEntry("key".getBytes("UTF-8"));
		DatabaseEntry dataEntry = new DatabaseEntry();
		db.get(null, keyEntry, dataEntry, LockMode.DEFAULT);
		Suppliers p = (Suppliers) dataBinding.entryToObject(dataEntry);
		System.out.println(p.getCategory());
	}

	/**
	 * test: read database
	 * @throws Exception
	 */
	public void testStore() throws Exception {

		EnvironmentConfig envConfig = new EnvironmentConfig();
		envConfig.setAllowCreate(true);
		env = new Environment(new File(".//src//util//importData"), envConfig);

		DatabaseConfig dbConfig = new DatabaseConfig();
		dbConfig.setAllowCreate(true);
		db = env.openDatabase(null, "myDB", dbConfig);
		classDB = env.openDatabase(null, "classDB", dbConfig);
		classCatalog = new StoredClassCatalog(classDB);

		EntryBinding dataBinding = new SerialBinding(classCatalog,Suppliers.class);

		Cursor cursor = null;
		CursorConfig config = new CursorConfig();
	    config.setDirtyRead(true);
	    cursor = db.openCursor(null, config);		// open cursor

		try {
			// Database and environment open omitted for brevity
			// Open the cursor. cursor = myDatabase.openCursor(null, null);
			// Cursors need a pair of DatabaseEntry objects to operate. These hold
			// the key and data found at any given position in the database.
			DatabaseEntry foundKey = new DatabaseEntry();
			DatabaseEntry foundData = new DatabaseEntry();
			// To iterate, just call getNext() until the last database record has been
			// read. All cursor operations return an OperationStatus, so just read
			// until we no longer see OperationStatus.SUCCESS
			while (cursor.getNext(foundKey, foundData, LockMode.DEFAULT) == OperationStatus.SUCCESS) {
				// getData() on the DatabaseEntry objects returns the byte array
				// held by that object. We use this to get a String value. If the
				// DatabaseEntry held a byte array representation of some other data
				// type (such as a complex object) then this operation would look
				// considerably different.
				String keyString = new String(foundKey.getData());
				
				Suppliers supp = (Suppliers)dataBinding.entryToObject(foundData);
				System.out.println("Key - Data : " + keyString + " - "
						+ supp.getCompanyName() + "");
			}
		} catch (DatabaseException de) {
			System.err.println("Error accessing database." + de);
		} finally {
			// Cursors must be closed.
			cursor.close();
			db.close();
			classDB.close();
			env.cleanLog();
			env.close();
		}

	}

	public void tearDown() throws Exception {
		db.close();
		classDB.close();
		env.cleanLog();
		env.close();
	}

	public static void main(String[] args) {
		Jedtion t = new Jedtion();
		try {
			// t.setUp();
			// Suppliers supp = new Suppliers();
			// supp.setCategory("fivefive");
			// t.testPut("5",supp);
			// t.testGet();
			// t.testStore();
                        // t.tearDown();
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

	}
}

 转：http://www.iteye.com/topic/227040