berkeleydb储存URL队列的简单实现增、删、查

//URL队列的实现，讲访问过的URL存到另外一个数组中，并删除队列中已经访问过的URL

package com.mycrawler.berkeleydb;

import java.io.File;

import com.sleepycat.je.Cursor;
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.LockMode;
import com.sleepycat.je.OperationStatus;
import com.sleepycat.je.Transaction;

public class OperatingDB {
	//讲URL写入队列中
	public boolean writerURL(String fileName, String url,
	String databaseDBName, String rankPage) {
	boolean mark = false;
	// 配置环境 https://community.oracle.com/thread/996592?start=0&tstart=0 问题地址
	EnvironmentConfig envConfig = new EnvironmentConfig();

	// 设置配置事务
	envConfig.setTransactional(true);
	// 如果不存在就创建环境
	envConfig.setAllowCreate(true);
	File file = new File(fileName);
	file.mkdirs();
	try {
	Environment exampleEnv = new Environment(file, envConfig);

	Transaction txn = exampleEnv.beginTransaction(null, null);

	DatabaseConfig dbConfig = new DatabaseConfig();
	dbConfig.setTransactional(true);
	dbConfig.setAllowCreate(true);
	dbConfig.setSortedDuplicates(false);
	Database exampleDb = exampleEnv.openDatabase(txn, databaseDBName,
	dbConfig);
	txn.commit();
	DatabaseEntry theKey = new DatabaseEntry(url.getBytes("utf-8"));
	DatabaseEntry theData = new DatabaseEntry(
	rankPage.getBytes("utf-8"));
	exampleDb.put(null, theKey, theData);
	exampleDb.close();
	exampleEnv.close();
	} catch (Exception e) {
	e.printStackTrace();
	mark = false;
	}

	return mark;
	}

	// 读取没有访问过的URL
	public String readerURL(String fileName, String databaseDBName) {
	// boolean mark = false;
	// 配置环境
	EnvironmentConfig envConfig = new EnvironmentConfig();
	// 设置配置事务
	envConfig.setTransactional(true);
	// 如果不存在就创建环境
	envConfig.setAllowCreate(true);
	File file = new File(fileName);
	String theKey = null;
	// file.mkdirs();
	try {

	Environment exampleEnv = new Environment(file, envConfig);
	// Transaction txn = exampleEnv.beginTransaction(null,null);

	DatabaseConfig dbConfig = new DatabaseConfig();

	dbConfig.setTransactional(true);
	dbConfig.setAllowCreate(true);
	dbConfig.setSortedDuplicates(false);

	Database myDB = exampleEnv.openDatabase(null, databaseDBName,
	dbConfig);
	// txn.commit();
	// txn = exampleEnv.beginTransaction(null,null);
	Cursor cursor = myDB.openCursor(null, null);
	DatabaseEntry foundKey = new DatabaseEntry();
	DatabaseEntry foundValue = new DatabaseEntry();
	// cursor.getPrev()与cursor.getNext()的区别：一个是从前往后读取，一个是从后往前读取
	// 这里讲访问遍历数据库全部数据while循环噶为if判断，则就只读取第一条数据
	if (cursor.getNext(foundKey, foundValue, LockMode.DEFAULT) == OperationStatus.SUCCESS) {
	theKey = new String(foundKey.getData(), "UTF-8");
	}
	cursor.close();
	myDB.close();
	exampleEnv.close();
	} catch (Exception e) {
	e.printStackTrace();
	}	
	return theKey;
	}

	// 读取已经爬取过的URL
	public String readerUsedURL(String fileName, String databaseDBName,
	String url) {
	// 配置环境
	EnvironmentConfig envConfig = new EnvironmentConfig();
	// 设置配置事务
	envConfig.setTransactional(true);
	// 如果不存在就创建环境
	envConfig.setAllowCreate(true);
	File file = new File(fileName);
	String theKey = null;
	// file.mkdirs();
	try {
	Environment exampleEnv = new Environment(file, envConfig);
	Transaction txn = exampleEnv.beginTransaction(null, null);
	DatabaseConfig dbConfig = new DatabaseConfig();
	dbConfig.setTransactional(true);
	dbConfig.setAllowCreate(true);
	dbConfig.setSortedDuplicates(false);
	Database myDB = exampleEnv.openDatabase(txn, databaseDBName,
	dbConfig);
	txn.commit();
	Cursor cursor = myDB.openCursor(null, null);
	DatabaseEntry foundKey = new DatabaseEntry();
	DatabaseEntry foundValue = new DatabaseEntry();
	// cursor.getPrev()与cursor.getNext()的区别：一个是从前往后读取，一个是从后往前读取
	// 这里讲访问遍历数据库全部数据while循环噶为if判断，则就只读取第一条数据
	while (cursor.getNext(foundKey, foundValue, LockMode.DEFAULT) == OperationStatus.SUCCESS) {
	theKey = new String(foundKey.getData(), "UTF-8");
	if (theKey.equals(url)) {
	return theKey;
	}
	}
	cursor.close();
	myDB.close();
	exampleEnv.close();
	} catch (Exception e) {
	e.printStackTrace();
	}

	return null;
	}

	// 删除已经读取过的URL
	public void deleteReadURL(String envHomePath, String databaseName,
	String key) {

	Environment mydbEnv = null;
	Database myDatabase = null;
	// 创建一个EnvironmentConfig配置对象
	EnvironmentConfig envCfg = new EnvironmentConfig();
	// 如果设置了true则表示当数据库环境不存在时候重新创建一个数据库环境，默认为false.
	envCfg.setAllowCreate(true);
	// 设置数据库缓存大小
	// envCfg.setCacheSize(1024 * 1024 * 20);
	// 事务支持,如果为true，则表示当前环境支持事务处理，默认为false，不支持事务处理。
	envCfg.setTransactional(true);
	try {
	mydbEnv = new Environment(new File(envHomePath), envCfg);
	DatabaseConfig dbCfg = new DatabaseConfig();
	// 如果数据库不存在则创建一个
	dbCfg.setAllowCreate(true);
	// 如果设置为true,则支持事务处理，默认是false，不支持事务
	dbCfg.setTransactional(true);
	myDatabase = mydbEnv.openDatabase(null, databaseName, dbCfg);
	DatabaseEntry keyEntry = new DatabaseEntry(key.getBytes("utf-8"));

	// 删除
	myDatabase.delete(null, keyEntry);
	} catch (Exception e) {
	e.printStackTrace();
	} finally {
	if (null != myDatabase) {
	try {
	myDatabase.close();
	} catch (DatabaseException e) {
	e.printStackTrace();
	}
	}
	if (null != mydbEnv) {
	// 在关闭环境前清理下日志
	try {
	mydbEnv.cleanLog();
	} catch (DatabaseException e) {
	e.printStackTrace();
	}
	try {
	mydbEnv.close();
	} catch (DatabaseException e) {
	e.printStackTrace();
	}
	mydbEnv = null;
	}
	}
	}

	public static void main(String[] args) {
	OperatingDB odb = new OperatingDB();
	// odb.writerURL( "c:/data/","www.163.com","data","123");
	// odb.writerURL( "c:/data/","www.baidu.com","data","123");
	String url = odb.readerURL("c:/data/", "data");
	if(url != null){
	odb.deleteReadURL("c:/data/","data",url);
	}
	else{
	System.out.println("url is null !!!");
	}
	}
}