在java中使用key-value型数据库Berkeley DB

除了关系型数据库外，还有key-value型数据库可以选择，在大型的查询系统中，key-value型数据库可以出色的完成某些任务。

Oracle的Berkeley DB就是一种key-value型数据库，本文简要介绍在java中使用Berkeley DB。

PartKey.java:

import java.io.Serializable;

public class PartKey implements Serializable
{

private String number;

public PartKey(String number) {
this.number = number;
}

public final String getNumber() {
return number;
}

public String toString() {
return "[PartKey: number=" + number + ']';
}

}

Weight.java

public class Weight implements Serializable
{
public final static String GRAMS = "grams";
public final static String OUNCES = "ounces";

private double amount;
private String units;

public Weight(double amount, String units)
{
this.amount = amount;
this.units = units;
}

public final double getAmount()
{
return amount;
}

public final String getUnits()
{
return units;
}

public String toString()
{
return "[" + amount + ' ' + units + ']';
}
}

PartData.java

public class PartData implements Serializable
{
private String name;
private String color;
private Weight weight;
private String city;

public PartData(String name, String color, Weight weight, String city)
{
this.name = name;
this.color = color;
this.weight = weight;
this.city = city;
}

public final String getName()
{
return name;
}

public final String getColor()
{
return color;
}

public final Weight getWeight()
{
return weight;
}

public final String getCity()
{
return city;
}

public String toString()
{
return "[PartData: name=" + name +
" color=" + color +
" weight=" + weight +
" city=" + city + ']';
}
}

简单的实体和key，与json有些类似。

SampleDatabase.java，建立数据库并创建日志

import com.sleepycat.bind.serial.StoredClassCatalog;
import com.sleepycat.je.Database;
import com.sleepycat.je.DatabaseConfig;
import com.sleepycat.je.DatabaseException;
import com.sleepycat.je.Environment;
import com.sleepycat.je.EnvironmentConfig;
import java.io.File;
import java.io.FileNotFoundException;

public class SampleDatabase {
private Environment env;
private static final String CLASS_CATALOG = "java_class_catalog";
private StoredClassCatalog javaCatalog;

private static final String PART_STORE = "part_store";
private Database partDb;

public SampleDatabase(String homeDirectory)
throws DatabaseException, FileNotFoundException
{
System.out.println("Opening environment in: " + homeDirectory);

EnvironmentConfig envConfig = new EnvironmentConfig();
envConfig.setTransactional(true);
envConfig.setAllowCreate(true);

env = new Environment(new File(homeDirectory), envConfig);

DatabaseConfig dbConfig = new DatabaseConfig();
dbConfig.setTransactional(true);
dbConfig.setAllowCreate(true);

partDb = env.openDatabase(null, PART_STORE, dbConfig);

Database catalogDb = env.openDatabase(null, CLASS_CATALOG, dbConfig);
javaCatalog = new StoredClassCatalog(catalogDb);

}

public void close()
throws DatabaseException
{
partDb.close();
javaCatalog.close();
env.close();
}

public final Environment getEnvironment()
{
return env;
}

public final Database getPartDatabase()
{
return partDb;
}

public StoredClassCatalog getClassCatalog() {
return javaCatalog;
}

}

SampleViews.java，将key-value绑定到数据库

import berkeley.entity.PartData;
import berkeley.entity.PartKey;

import com.sleepycat.bind.EntryBinding;
import com.sleepycat.bind.serial.ClassCatalog;
import com.sleepycat.bind.serial.SerialBinding;
import com.sleepycat.collections.StoredEntrySet;
import com.sleepycat.collections.StoredMap;

public class SampleViews {
private StoredMap partMap;

public SampleViews(SampleDatabase db)
{
ClassCatalog catalog = db.getClassCatalog();
EntryBinding partKeyBinding = new SerialBinding(catalog, PartKey.class);
EntryBinding partValueBinding = new SerialBinding(catalog, PartData.class);

partMap = new StoredMap(db.getPartDatabase(),
partKeyBinding,
partValueBinding,
true);

}

public final StoredMap getPartMap()
{
return partMap;
}

public final StoredEntrySet getPartEntrySet()
{
return (StoredEntrySet) partMap.entrySet();
}
}

Sample.java

import java.io.FileNotFoundException;
import java.util.Iterator;
import java.util.Map;

import berkeley.db.SampleDatabase;
import berkeley.db.SampleViews;
import berkeley.entity.PartData;
import berkeley.entity.PartKey;
import berkeley.entity.Weight;

import com.sleepycat.collections.TransactionRunner;
import com.sleepycat.collections.TransactionWorker;
import com.sleepycat.je.DatabaseException;

public class Sample {
private SampleDatabase db;
private SampleViews views;

private Sample(String homeDir)
throws DatabaseException, FileNotFoundException
{
db = new SampleDatabase(homeDir);
views = new SampleViews(db);
}

private void close()
throws DatabaseException{
db.close();
}

private void run()
throws Exception
{
TransactionRunner runner =
new TransactionRunner(db.getEnvironment());
runner.run(new PopulateDatabase());
runner.run(new PrintDatabase());

}

private class PrintDatabase implements TransactionWorker
{
public void doWork()
throws Exception{
addParts();
}

private void addParts()
{
Map parts = views.getPartMap();
if (parts.isEmpty())
{
System.out.println("Adding Parts");
parts.put(new PartKey("P1"),
new PartData("Nut", "Red",
new Weight(12.0, Weight.GRAMS),
"London"));
parts.put(new PartKey("P2"),
new PartData("Bolt", "Green",
new Weight(17.0, Weight.GRAMS),
"Paris"));
parts.put(new PartKey("P3"),
new PartData("Screw", "Blue",
new Weight(17.0, Weight.GRAMS),
"Rome"));
parts.put(new PartKey("P4"),
new PartData("Screw", "Red",
new Weight(14.0, Weight.GRAMS),
"London"));
parts.put(new PartKey("P5"),
new PartData("Cam", "Blue",
new Weight(12.0, Weight.GRAMS),
"Paris"));
parts.put(new PartKey("P6"),
new PartData("Cog", "Red",
new Weight(19.0, Weight.GRAMS),
"London"));
}

}
}

private class PopulateDatabase implements TransactionWorker
{
public void doWork()
throws Exception
{
printEntries("Parts",
views.getPartEntrySet().iterator());

}

private void printEntries(String label, Iterator iterator)
{
System.out.println("/n--- " + label + " ---");
while (iterator.hasNext())
{
Map.Entry entry = (Map.Entry) iterator.next();

System.out.println(entry.getKey().toString());
System.out.println(entry.getValue().toString());
}

}

}

public PartData getParts() {
return (PartData) views.getPartMap().get(new PartKey("P6"));
}

public static void main(String[] args)
{
Sample sample = null;
try
{
System.out.println("/nRunning sample: " + Sample.class);
String homeDir = "C:/tmp";
sample = new Sample(homeDir);
sample.run();
System.out.println(sample.getParts());
}
catch (Exception e)
{
e.printStackTrace();
}
finally
{
if (sample != null)
{
try
{
sample.close();
}
catch (Exception e)
{
System.err.println("Exception during database close:");
e.printStackTrace();
}
}
}
}

}

运行结果：

Running sample: class berkeley.Sample
Opening environment in: C:/tmp

--- Parts ---
[PartKey: number=P1]
[PartData: name=Nut color=Red weight=[12.0 grams] city=London]
[PartKey: number=P2]
[PartData: name=Bolt color=Green weight=[17.0 grams] city=Paris]
[PartKey: number=P3]
[PartData: name=Screw color=Blue weight=[17.0 grams] city=Rome]
[PartKey: number=P4]
[PartData: name=Screw color=Red weight=[14.0 grams] city=London]
[PartKey: number=P5]
[PartData: name=Cam color=Blue weight=[12.0 grams] city=Paris]
[PartKey: number=P6]
[PartData: name=Cog color=Red weight=[19.0 grams] city=London]
[PartData: name=Cog color=Red weight=[19.0 grams] city=London]

再把 sample.run() 注释掉看看：

[PartData: name=Cog color=Red weight=[19.0 grams] city=London]