JDBM2 提供了 HashMap 和 TreeMap 的磁盘存储功能，简单易用，用于持久化数据。特别适合用于嵌入到其他应用程序中。
HelloWorld.java
import java.io.IOException;
import jdbm.PrimaryTreeMap;
import jdbm.RecordManager;
import jdbm.RecordManagerFactory;
/**
* This program demonstrates basic JDBM usage.
*
* @author Jan Kotek
*
*/
public class HelloWorld {
public static void main(String[] args) throws IOException {
/** create (or open existing) database */
String fileName = "helloWorld";
RecordManager recMan = RecordManagerFactory.createRecordManager(fileName);
/** Creates TreeMap which stores data in database.
* Constructor method takes recordName (something like SQL table name)*/
String recordName = "firstTreeMap";
PrimaryTreeMap<Integer,String> treeMap = recMan.treeMap(recordName);
/** add some stuff to map*/
treeMap.put(1, "One");
treeMap.put(2, "Two");
treeMap.put(3, "Three");
System.out.println(treeMap.keySet());
// > [1, 2, 3]
/** Map changes are not persisted yet, commit them (save to disk) */
recMan.commit();
System.out.println(treeMap.keySet());
// > [1, 2, 3]
/** Delete one record. Changes are not commited yet, but are visible. */
treeMap.remove(2);
System.out.println(treeMap.keySet());
// > [1, 3]
/** Did not like change. Roolback to last commit (undo record remove). */
recMan.rollback();
/** Key 2 was recovered */
System.out.println(treeMap.keySet());
// > [1, 2, 3]
/** close record manager */
recMan.close();
}
}
HelloWorld2.java
import java.io.IOException;
import java.io.Serializable;
import jdbm.PrimaryStoreMap;
import jdbm.RecordManager;
import jdbm.RecordManagerFactory;
import jdbm.SecondaryKeyExtractor;
import jdbm.SecondaryTreeMap;
/**
* More advanced example to demonstrate Map usage.
*
* @author Jan Kotek
*
*/
public class HelloWorld2 {
static class Person implements Serializable{
/** never forget this, very important for serialization*/
private static final long serialVersionUID = -3321252970661193623L;
final String name;
final String town;
final String country;
/** some data to object class bigger */
final byte[] balast = new byte[1024];
public Person(String name, String town, String country) {
this.name = name;
this.town = town;
this.country = country;
}
@Override
public String toString() {
return "Person [name=" + name + ", town=" + town + ", country=" + country + "]";
}
/** snip getters and setters*/
}
public static void main(String[] args) throws IOException {
RecordManager recman = RecordManagerFactory.
createRecordManager("HelloWorld2");
/**
* Create primary map which is used to store records.
* Data can be also stored in PrimaryTreeMap and PrimaryHashMap,
* but this is more efficient for large objects.
*/
PrimaryStoreMap<Long,Person> main = recman.storeMap("recman");
/**
* Create secondary index which points to Person name.
* SecondaryMap is readonly, it is updated by PrimaryMap.
*
* Secondary map have three types,
* first is type of secondary index (string),
* second and third are copied from primary map.
*/
SecondaryTreeMap<String, Long, Person> nameIndex = main.secondaryTreeMap("nameIndex",
new SecondaryKeyExtractor<String, Long, Person>() {
public String extractSecondaryKey(Long key, Person value) {
return value.name;
}
});
/**
* Another secondary map which points to town and country
*/
SecondaryTreeMap<String, Long, Person> townIndex = main.secondaryTreeMap("townIndex",
new SecondaryKeyExtractor<String, Long, Person>() {
public String extractSecondaryKey(Long key, Person value) {
/**
* Note format of map key
*/
return value.country+"/"+value.town;
}
});
/**
* And very simple index of Evil family members
*/
SecondaryTreeMap<Boolean, Long, Person> evilIndex = main.secondaryTreeMap("evilIndex",
new SecondaryKeyExtractor<Boolean, Long, Person>() {
public Boolean extractSecondaryKey(Long key, Person value) {
return value.name.contains("Evil");
}
});
/**
* Clean up, if this example was run more times.
* All secondary indexes are updated automatically.
*/
main.clear();
/**
* Add some data.
* StoreMap does not have usuall 'put' method.
* Key is generated by Store, so use 'putValue' instead
*/
main.putValue(new Person("James Bond","London","UK"));
main.putValue(new Person("Austin Powers","London","UK"));
main.putValue(new Person("Dr Evil","Vulcano Island","Ocean"));
main.putValue(new Person("Scott Evil","Vulcano Island","Ocean"));
main.putValue(new Person("Vanessa Kensington","London","UK"));
main.putValue(new Person("Alotta Fagina","Las Vegas","USA"));
/**
* Persists inserted values
*/
recman.commit();
/**
* Get persons with name Austin Powers
*/
System.out.println();
System.out.println("Austin Powers: ");
for(Person person:nameIndex.getPrimaryValues("Austin Powers")){
System.out.println(" "+person);
}
/**
* Print all Persons who lives on Vulcano Island.
* First we must obtain key from primary map,
* then
*/
System.out.println();
System.out.println("Persons on Vulcano Island: ");
for(Person person:townIndex.getPrimaryValues("Ocean/Vulcano Island")){
System.out.println(" "+person);
}
/**
* Get everyone who is Evil
*/
System.out.println();
System.out.println("Evil family: ");
for(Person person:evilIndex.getPrimaryValues(true)){
System.out.println(" "+person);
}
recman.close();
}
}
HugeData.java
import java.io.IOException;
import jdbm.PrimaryTreeMap;
import jdbm.RecordManager;
import jdbm.RecordManagerFactory;
/**
*
* This examples generates huge map of data.
* It inserts 10 000 000 records, it takes about 10 minutes to finish.
*
* @author Jan Kotek
*
*/
public class HugeData {
public static void main(String[] args) throws IOException {
/** open db */
RecordManager recman = RecordManagerFactory.createRecordManager( "hugedata");
PrimaryTreeMap<Long, String> m = recman.treeMap("hugemap");
/** insert 1e7 records */
for(long i = 0;i<1e8;i++){
m.put(i, "aa"+i);
if(i%1e5==0){
/** Commit periodically, otherwise program would run out of memory */
recman.commit();
System.out.println(i);
}
}
recman.commit();
recman.close();
System.out.println("DONE");
}
}
Persons1.java
import java.io.IOException;
import java.io.Serializable;
import jdbm.PrimaryTreeMap;
import jdbm.RecordManager;
import jdbm.RecordManagerFactory;
import jdbm.SecondaryKeyExtractor;
import jdbm.SecondaryTreeMap;
/**
* Demonstrates more advanced usage of JDBM:
* Secondary maps, 1:N relations.
*
* @author Jan Kotek
*
*/
public class Persons1 {
static class Person implements Serializable{
/** field used for person identification (primary key)**/
String name;
/** persisted with Person (embedded field in JPA terms) **/
Address adress;
/** N:1 relation */
String fatherName;
/** constructor, getters and setters are excluded for simplicity */
public Person(String name, Address adress,String fatherName) {
super();
this.name = name;
this.adress = adress;
this.fatherName = fatherName;
}
public String toString(){
return "Person["+name+"]";
}
public int hashCode() {
return name == null? 0 : name.hashCode();
}
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null || !(obj instanceof Person))
return false;
Person other = (Person) obj;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
return true;
}
}
static class Address implements Serializable{
String streetName;
String town;
String country;
public Address(String streetName, String town, String country) {
super();
this.streetName = streetName;
this.town = town;
this.country = country;
}
}
public static void main(String[] args) throws IOException {
//init Record Manager and dao
RecordManager recman = RecordManagerFactory.createRecordManager("persons1");
PrimaryTreeMap<String,Person> personsByName = recman.treeMap("personsByName");
SecondaryTreeMap<String, String, Person> personsByTown =
personsByName.secondaryTreeMap("personsByTown",
new SecondaryKeyExtractor<String, String, Person>() {
public String extractSecondaryKey(String key,Person value) {
return value.adress.town;
}
});
//create a few persons
Person patrick = new Person("Patrick Moore",
new Address("First street", "Athlone","Ireland"),
null);
personsByName.put(patrick.name, patrick);
Person jack = new Person("Jack Moore",
new Address("First street", "Athlone","Ireland"),
patrick.name);
personsByName.put(jack.name, jack);
Person paul = new Person("Paul Moore",
new Address("Shop street", "Galway","Ireland"),
patrick.name);
personsByName.put(paul.name, paul );
System.out.println("Number of persons: "+personsByName.size());
System.out.println("Persons with name Patrick Moore: "+personsByName.get("Patrick Moore"));
System.out.println("Name of persons living in Galway: "+personsByTown.get("Galway"));
System.out.println("Father of Paul Moore: "+
personsByName.get(
personsByName.get("Paul Moore").fatherName
));
}
}
Persons2.java
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import jdbm.InverseHashView;
import jdbm.PrimaryStoreMap;
import jdbm.RecordManager;
import jdbm.RecordManagerFactory;
import jdbm.SecondaryKeyExtractor;
import jdbm.SecondaryTreeMap;
import jdbm.Serializer;
import jdbm.SerializerInput;
import jdbm.SerializerOutput;
import jdbm.helper.Serialization;
/**
* Demonstrates more advanced usage of JDBM:
* Secondary maps, 1:N relations.
*
* @author Jan Kotek
*
*/
public class Persons2 {
static class Person implements Serializable{
/** field used for person identification (primary key)**/
String name;
/** persisted with Person (embedded field in JPA terms) **/
Address adress;
/** N:1 relation */
Person father;
/** constructor, getters and setters are excluded for simplicity */
public Person(String name, Address adress,Person father) {
super();
this.name = name;
this.adress = adress;
this.father = father;
}
public String toString(){
return "Person["+name+"]";
}
public int hashCode() {
return name == null? 0 : name.hashCode();
}
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null || !(obj instanceof Person))
return false;
Person other = (Person) obj;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
return true;
}
}
static class Address implements Serializable{
String streetName;
String town;
String country;
public Address(String streetName, String town, String country) {
super();
this.streetName = streetName;
this.town = town;
this.country = country;
}
}
/** dao object which handles Person persistence */
static class PersonDao implements Serializer<Person>{
/**
* This is map in which persons are inserted in.
* Key is number assigned by store (recordId).
* You should prefer recordId as primary index, it is more flexible.
*/
PrimaryStoreMap<Long,Person> persons;
/** Inverse view on person, it helps to find recordId which belongs to person */
InverseHashView< Long, Person> personsInverse;
/**
* Secondary view on persons, which identifies person by name.
* This map is readonly, it is autoupdated by JDBM as primary map changes.
* Key is name, value is recordId ( key from primary map),
* third parameter is Person (value from primary map)
*/
SecondaryTreeMap<String, Long, Person> personsByName;
/**
* Secondary view on persons, which identifies person its town
* This map is readonly, it is autoupdated by JDBM as primary map changes.
* Key is town name extracted from primary table,
* value is recordId ( key from primary map),
* third parameter is town from (value from primary map)
*/
SecondaryTreeMap<String, Long, Person> personsByTown;
public PersonDao(RecordManager recman) {
persons = recman.storeMap("persons",this);
personsInverse = persons.inverseHashView("personsInverse");
personsByName = persons.secondaryTreeMap("personsByName",
new SecondaryKeyExtractor<String, Long, Person>() {
public String extractSecondaryKey(Long key, Person value) {
return value.name;
}});
personsByTown = persons.secondaryTreeMap("personsByTown",
new SecondaryKeyExtractor<String, Long, Person>() {
public String extractSecondaryKey(Long key, Person value) {
if(value.adress == null)
return null;
return value.adress.town;
}});
}
public Person personByRecordId(Long recid){
return persons.get(recid);
}
public Person personByName(String name){
if(!personsByName.containsKey(name))
return null;
Iterator<Long> iter = personsByName.get(name).iterator();
if(iter.hasNext())
return personsByName.getPrimaryValue(iter.next());
else
return null;
}
public Iterable<Person> personsByTown(String name){
List<Person> ret = new ArrayList<Person>();
for(Long l: personsByTown.get(name)){
ret.add(personsByTown.getPrimaryValue(l));
}
return ret;
}
public void insertPerson(Person person){
Long recid = personsInverse.findKeyForValue(person);
if(recid == null)
persons.putValue(person);
else
persons.put(recid, person);
}
public Person deserialize(SerializerInput in) throws IOException, ClassNotFoundException {
String name = in.readObject();
Address address = in.readObject();
Person father = persons.get(in.readObject());
Person p = new Person(name,address,father);
return p;
}
public void serialize(SerializerOutput out, Person obj)
throws IOException {
out.writeObject(obj.name);
out.writeObject(obj.adress);
out.writeObject(findOrPersistPerson(obj.father));
}
protected Long findOrPersistPerson(Person person){
if(person == null)
return null;
Long recid = personsInverse.findKeyForValue(person);
if(recid == null)
recid = persons.putValue(person);
return recid;
}
}
public static void main(String[] args) throws IOException {
//init Record Manager and dao
RecordManager recman = RecordManagerFactory.createRecordManager("persons2");
PersonDao dao = new PersonDao(recman);
//create a few persons
Person patrick = new Person("Patrick Moore",
new Address("First street", "Athlone","Ireland"),
null);
Person jack = new Person("Jack Moore",
new Address("First street", "Athlone","Ireland"),
patrick);
Person paul = new Person("Paul Moore",
new Address("Shop street", "Galway","Ireland"),
patrick);
//now store all this stuff
dao.insertPerson(jack);
dao.insertPerson(patrick);
dao.insertPerson(paul);
System.out.println("Number of persons: "+dao.persons.size());
System.out.println("Persons with name Patrick Moore: "+dao.personByName("Patrick Moore"));
System.out.println("Persons living in Galway: "+dao.personsByTown("Galway"));
System.out.println("Father of Paul Moore: "+dao.personByName("Paul Moore").father);
}
}
原创文章，作者：Maggie-Hunter，如若转载，请注明出处：https://blog.ytso.com/10478.html