Berkeley db 基本操作代码(基础)
最近学习Berkeley DB Java Edition(JE版)。写一个浅显的例子，入门吧～
至于什么是bdb,请参考 bdb中国研发团队的这篇文章
package com.berkeley.dbje;
import java.io.File;
import java.io.UnsupportedEncodingException;
import com.sleepycat.bind.tuple.IntegerBinding;
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.LockMode;
import com.sleepycat.je.OperationStatus;
public class MyBdb {
private static MyBdb myBdb = null;
private EnvironmentConfig envConfig;
private Environment env;
private DatabaseConfig dbConfig;
private Database db;
private MyBdb(){}//prevent others to construct the class object
public static MyBdb newInstance(){//single alone pattern,must using static
if(myBdb == null){
myBdb = new MyBdb();
}
return myBdb;
}
//initialize the environment and database
public void initEnv(){
try{
File file = new File("./db/");
if(!file.exists()) file.mkdirs();
envConfig = new EnvironmentConfig();
envConfig.setAllowCreate(true);
env = new Environment(file,envConfig);
dbConfig = new DatabaseConfig();
dbConfig.setAllowCreate(true);
db = env.openDatabase(null, "vertext", dbConfig);//use env to open db
}catch(Exception e){
e.printStackTrace();
}
}
//close env and database
public void close(){
try{
//close the database first! and then close the environemnt
if(db!=null){
db.close();
}
if(env!=null){
env.close();
}
}catch(Exception e){
e.printStackTrace();
}
}
//insert key(int)&value(String)
public int insert(int key,String value){
try {
DatabaseEntry tkey = new DatabaseEntry();
IntegerBinding.intToEntry(key, tkey);//change int to entry(object)
//class String can get bytes-->DatabaseEntry(byte[] data
DatabaseEntry tvalue = new DatabaseEntry(value.getBytes("UTF-8"));
//another method to change String into entry(object)
//StringBinding.stringToEntry(value, tvalue);
//you have finished changing object to entry,then put to db
if(OperationStatus.SUCCESS != db.put(null, tkey, tvalue)){
System.out.println("database error:fail to insert data !");
return -1;
}
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
return -2;
}
return 0;
}
//through key(int) to get data(String)
public String getRecord(int key){
String value = null;
try{
DatabaseEntry tkey = new DatabaseEntry();
IntegerBinding.intToEntry(key, tkey);
DatabaseEntry tvalue = new DatabaseEntry();
if(OperationStatus.SUCCESS != db.get(null, tkey, tvalue, LockMode.DEFAULT)){
System.out.println("database error:fail to get data records!");
}else{//get the record and change
value = new String(tvalue.getData());
}
}catch(Exception e){
e.printStackTrace();
}
return value;
}
//insert object
//object can be considered as key or value!
public int insert(int key ,ObjectData oData){
try{
DatabaseEntry tkey = new DatabaseEntry();
IntegerBinding.intToEntry(key, tkey);
DatabaseEntry tvalue = new DatabaseEntry();
ObjectTupleBinding obind = new ObjectTupleBinding();
obind.objectToEntry(oData, tvalue);//encapsulate key&value to One Entry
if(OperationStatus.SUCCESS != db.put(null, tkey, tvalue)){
System.out.println("database error:fail to insert data");
return -1;
}
}catch(Exception e){
e.printStackTrace();
return -2;
}
return 0;
}
//get the object data
public ObjectData getRecord(int key,boolean flag){
ObjectData od = null;
try{
ObjectTupleBinding oBind = new ObjectTupleBinding();
DatabaseEntry tkey = new DatabaseEntry();
IntegerBinding.intToEntry(key, tkey);
DatabaseEntry tvalue = new DatabaseEntry();
if(OperationStatus.SUCCESS == db.get(null, tkey, tvalue, LockMode.DEFAULT)){
od = (ObjectData)oBind.entryToObject(tvalue);
}
}catch(Exception e){
e.printStackTrace();
}
return od;
}
}
以上是berkeley db的基本操作。初始化environment和database等、插入数据、读取数据！
实体对象类ObjectData代码如下：
package com.berkeley.dbje;
public class ObjectData {
private int key;
private String name;
private double sum;
private long length;
public ObjectData(int key,String name,double sum,long length){
this.key = key;
this.name = name;
this.sum = sum;
this.length = length;
}
public ObjectData(){
}
public int getKey() {
return key;
}
public void setKey(int key) {
this.key = key;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getSum() {
return sum;
}
public void setSum(double sum) {
this.sum = sum;
}
public long getLength() {
return length;
}
public void setLength(long length) {
this.length = length;
}
}
要将对象数据存入数据库，首先必须将对象变成DatabaseEntry对象，因此两者只要需要一个转化的类：ObjectDataTupleBinding类：
package com.berkeley.dbje;
import com.sleepycat.bind.tuple.TupleBinding;
import com.sleepycat.bind.tuple.TupleInput;
import com.sleepycat.bind.tuple.TupleOutput;
/**
* identify the regular of data convert
* @author sang
*
*/
public class ObjectTupleBinding extends TupleBinding{
@Override
public Object entryToObject(TupleInput in) {
//order is very important
ObjectData od = new ObjectData();
od.setKey(in.readInt());
od.setName(in.readString());
od.setSum(in.readDouble());
od.setLength(in.readLong());
return od;
}
@Override
public void objectToEntry(Object obj, TupleOutput out) {
//invert object to class ObjectData
ObjectData od = (ObjectData)obj;
// Write the data to the TupleOutput (a DatabaseEntry).
// Order is important. The first data written will be
// the first bytes used by the default comparison routines.
out.writeInt(od.getKey());
out.writeString(od.getName());
out.writeDouble(od.getSum());
out.writeLong(od.getLength());
//then the data will be written to database
}
}
test代码如下：
package com.berkeley.dbje;
public class MainTest {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
MyBdb myBdb = MyBdb.newInstance();
ObjectData od = new ObjectData();
myBdb.initEnv();
myBdb.insert(12, "ad");
myBdb.insert(13,new ObjectData(1,"sa",12,1));
System.out.println(myBdb.getRecord(12));
od = myBdb.getRecord(13,true);
if(od != null){
System.out.println(od.getName());
}
myBdb.close();
}
}
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