berkeleydb储存URL队列的简单实现增、删、查(二)
BName, 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.o