Berkeley DB之JE入门

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文件数据库。JE具有如下优点:

1. 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。
2. 多线程支持，JE使用超时的方式来处理线程间的死琐问题。
3. Database都采用简单的key/value对应的形式。
4. 支持事物。
5. 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。
6. 支持RAM缓冲，这样就能减少频繁的IO操作。
7. 支持日志。
8. 数据备份和恢复。
9. 游标支持。、

获取JE安装环境

JE下载地址:http://download.oracle.com/otn/berkeley-db/je-7.5.11.zip
解压包后,把JE_HOME/lib/je-.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
相关源代码见JE_HOME/src/.

代码

JE操作类

package je_test;
import java.io.File;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;

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.Environment;
import com.sleepycat.je.EnvironmentConfig;
import com.sleepycat.je.LockConflictException;
import com.sleepycat.je.LockMode;
import com.sleepycat.je.OperationStatus;
import com.sleepycat.je.Transaction;
import com.sleepycat.je.TransactionConfig;

public class BerkeleyDBUtil {

	// 数据库环境
	private Environment env = null;

	// 数据库
	private static Database frontierDatabase = null;

	// 数据库名
	private static String dbName = "frontier_database";

	public BerkeleyDBUtil(String homeDirectory) {

		// 1、创建EnvironmentConfig
		EnvironmentConfig envConfig = new EnvironmentConfig();
		envConfig.setTransactional(true);
		envConfig.setAllowCreate(true);

		// 2、使用EnvironmentConfig配置Environment
		env = new Environment(new File(homeDirectory), envConfig);

		// 3、创建DatabaseConfig
		DatabaseConfig dbConfig = new DatabaseConfig();
		dbConfig.setTransactional(true);
dbConfig.setAllowCreate(true);

		// 4、使用Environment与DatabaseConfig打开Database
		frontierDatabase = env.openDatabase(null, dbName, dbConfig);

	}

	/** 向数据库中写入记录，并判断是否可以有重复数据。 传入key和value
		* 若可以有重复数据，则直接使用put()即可，若不能有重复数据，则使用putNoOverwrite()。
	*/
	public boolean writeToDatabase(String key, String value, boolean isOverwrite) {
		try {
			// 设置key/value,注意DatabaseEntry内使用的是bytes数组
			DatabaseEntry theKey = new DatabaseEntry(key.getBytes("UTF-8"));
			DatabaseEntry theData = new DatabaseEntry(value.getBytes("UTF-8"));
			OperationStatus status = null;
			Transaction txn = null;
			try {
				// 1、Transaction配置
				TransactionConfig txConfig = new TransactionConfig();
				txConfig.setSerializableIsolation(true);
				txn = env.beginTransaction(null, txConfig);
				// 2、写入数据
				if (isOverwrite) {
					status = frontierDatabase.put(txn, theKey, theData);
				} else {
					status = frontierDatabase.putNoOverwrite(txn, theKey, theData);
				}
				txn.commit();
				if (status == OperationStatus.SUCCESS) {
					System.out.println("向数据库" + dbName + "中写入:" + key + "," + value);
					return true;
				} else if (status == OperationStatus.KEYEXIST) {
					System.out.println("向数据库" + dbName + "中写入:" + key + "," + value + "失败,该值已经存在");
					return false;
				} else {
					System.out.println("向数据库" + dbName + "中写入:" + key + "," + value + "失败");
					return false;
				}
			} catch (LockConflictException lockConflict) {
				txn.abort();
				System.out.println("向数据库" + dbName + "中写入:" + key + "," + value + "出现lock异常");
				return false;
			}
		} catch (Exception e) {
			// 错误处理
			System.out.println("向数据库" + dbName + "中写入:" + key + "," + value + "出现错误");
			return false;
		}
	}

	/*
	 * 从数据库中读出数据 传入key 返回value
	 */
	public String readFromDatabase(String key) {
		try {
			DatabaseEntry theKey = new DatabaseEntry(key.getBytes("UTF-8"));
			DatabaseEntry theData = new DatabaseEntry();
			Transaction txn = null;
			try {
				// 1、配置 Transaction相关信息
				TransactionConfig txConfig = new TransactionConfig();
				txConfig.setSerializableIsolation(true);
				txn = env.beginTransaction(null, txConfig);
				// 2、读取数据
				OperationStatus status = frontierDatabase.get(txn, theKey, theData, LockMode.DEFAULT);
				txn.commit();
				if (status == OperationStatus.SUCCESS) {
					// 3、将字节转换成String
					byte[] retData = theData.getData();
					String value = new String(retData, "UTF-8");
					System.out.println("从数据库" + dbName + "中读取:" + key + "," + value);
					return value;
				} else {
					System.out.println("No record found for key '" + key + "'.");
					return "";
				}
			} catch (LockConflictException lockConflict) {
				txn.abort();
				System.out.println("从数据库" + dbName + "中读取:" + key + "出现lock异常");
				return "";
			}
		} catch (UnsupportedEncodingException e) {
			e.printStackTrace();
			return "";
		}
	}

	/*
	 * 遍历数据库中的所有记录，返回list
	 */
	public ArrayList<String> getEveryItem() {
		// TODO Auto-generated method stub
		System.out.println("===========遍历数据库" + dbName + "中的所有数据==========");
		Cursor myCursor = null;
		ArrayList<String> resultList = new ArrayList<String>();
		Transaction txn = null;
		try {
			txn = this.env.beginTransaction(null, null);
			CursorConfig cc = new CursorConfig();
			cc.setReadCommitted(true);
			if (myCursor == null)
			myCursor = frontierDatabase.openCursor(txn, cc);
			DatabaseEntry foundKey = new DatabaseEntry();
			DatabaseEntry foundData = new DatabaseEntry();
			// 使用cursor.getPrev方法来遍历游标获取数据
			if (myCursor.getFirst(foundKey, foundData, LockMode.DEFAULT) == OperationStatus.SUCCESS) {
				String theKey = new String(foundKey.getData(), "UTF-8");
				String theData = new String(foundData.getData(), "UTF-8");
				resultList.add(theKey);
				System.out.println("Key | Data : " + theKey + " | " + theData + "");
				while (myCursor.getNext(foundKey, foundData, LockMode.DEFAULT) == OperationStatus.SUCCESS) {
					theKey = new String(foundKey.getData(), "UTF-8");
					theData = new String(foundData.getData(), "UTF-8");
					resultList.add(theKey);
					System.out.println("Key | Data : " + theKey + " | " + theData + "");
				}
			}
			myCursor.close();
			txn.commit();
			return resultList;
		} catch (UnsupportedEncodingException e) {
			e.printStackTrace();
			return null;
		} catch (Exception e) {
			System.out.println("getEveryItem处理出现异常");
			txn.abort();
			if (myCursor != null) {
				myCursor.close();
			}
			return null;
		}
	}

	/*
	 * 根据key值删除数据库中的一条记录
	 */
	public boolean deleteFromDatabase(String key) {
		boolean success = false;
		long sleepMillis = 0;
		for (int i = 0; i < 3; i++) {
			if (sleepMillis != 0) {
			try {
				Thread.sleep(sleepMillis);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			sleepMillis = 0;
		}
		Transaction txn = null;
		try {
			// 1、使用cursor.getPrev方法来遍历游标获取数据
			TransactionConfig txConfig = new TransactionConfig();
			txConfig.setSerializableIsolation(true);
			txn = env.beginTransaction(null, txConfig);
			DatabaseEntry theKey;
			theKey = new DatabaseEntry(key.getBytes("UTF-8"));

			// 2、删除数据 并提交
			OperationStatus res = frontierDatabase.delete(txn, theKey);
			txn.commit();
			if (res == OperationStatus.SUCCESS) {
				System.out.println("从数据库" + dbName + "中删除:" + key);
				success = true;
				return success;
			} else if (res == OperationStatus.KEYEMPTY) {
				System.out.println("没有从数据库" + dbName + "中找到:" + key + "。无法删除");
			} else {
				System.out.println("删除操作失败，由于" + res.toString());
			}
			return false;
		} catch (UnsupportedEncodingException e) {
			e.printStackTrace();
			return false;
		} catch (LockConflictException lockConflict) {
			System.out.println("删除操作失败，出现lockConflict异常");
			sleepMillis = 1000;
			continue;
		} finally {
			if (!success) {
				if (txn != null) {
					txn.abort();
				}
			}
		}
		return false;
	}

	public void closeDB() {
		if (frontierDatabase != null) {
			frontierDatabase.close();
		}
		if (env != null) {
			env.close();
		}
	}
}

JE测试类

package je_test;

public class BerkeleyDBUtilTest {  
    
    private BerkeleyDBUtil dbUtil = new BerkeleyDBUtil("/Users/liuzhixiong/Desktop/envhome/");  
 
    public static void main(String[] args) {
		new BerkeleyDBUtilTest().testWriteToDatabase();
		String key = "2";
    	String value = new BerkeleyDBUtilTest().testReadFromDatabase(key);
    	System.out.println("value=" + value);
    }

    public void testWriteToDatabase() {  
        for (int i = 0; i < 10; i++){  
        	dbUtil.writeToDatabase(i+"", "学生"+i, true);  
	    }  
    }  

    public String testReadFromDatabase(String key) {  
        String value = dbUtil.readFromDatabase(key);
        return value;
    }  

    public int testGetEveryItem() {  
        int size = dbUtil.getEveryItem().size();  
        return size;
    }  

    public void testDeleteFromDatabase() {  
        dbUtil.deleteFromDatabase("4");  
    }  
 
    public void cleanup() {  
        dbUtil.closeDB();  
    } 
}