java JDBM2 的几个简单实例
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); } }