//$Id: LockMode.java 9581 2006-03-09 15:50:15Z epbernard $
package org.hibernate;
import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;
/**
* Instances represent a lock mode for a row of a relational
* database table. It is not intended that users spend much
* time worrying about locking since Hibernate usually
* obtains exactly the right lock level automatically.
* Some "advanced" users may wish to explicitly specify lock
* levels.
*
* @see Session#lock(Object,LockMode)
* @author Gavin King
*/
public final class LockMode implements Serializable {
private final int level;
private final String name;
private static final Map INSTANCES = new HashMap();
private LockMode(int level, String name) {
this.level=level;
this.name=name;
}
public String toString() {
return name;
}
/**
* Check if this lock mode is more restrictive than the given lock mode.
*
* @param mode LockMode to check
* @return true if this lock mode is more restrictive than given lock mode
*/
public boolean greaterThan(LockMode mode) {
return level > mode.level;
}
/**
* Check if this lock mode is less restrictive than the given lock mode.
*
* @param mode LockMode to check
* @return true if this lock mode is less restrictive than given lock mode
*/
public boolean lessThan(LockMode mode) {
return level < mode.level;
}
/**
* No lock required. If an object is requested with this lock
* mode, a <tt>READ</tt> lock will be obtained if it is
* necessary to actually read the state from the database,
* rather than pull it from a cache.<br>
* <br>
* This is the "default" lock mode.
*/
public static final LockMode NONE = new LockMode(0, "NONE");
/**
* A shared lock. Objects in this lock mode were read from
* the database in the current transaction, rather than being
* pulled from a cache.
*/
public static final LockMode READ = new LockMode(5, "READ");
/**
* An upgrade lock. Objects loaded in this lock mode are
* materialized using an SQL <tt>select ... for update</tt>.
*/
public static final LockMode UPGRADE = new LockMode(10, "UPGRADE");
/**
* Attempt to obtain an upgrade lock, using an Oracle-style
* <tt>select for update nowait</tt>. The semantics of
* this lock mode, once obtained, are the same as
* <tt>UPGRADE</tt>.
*/
public static final LockMode UPGRADE_NOWAIT = new LockMode(10, "UPGRADE_NOWAIT");
/**
* A <tt>WRITE</tt> lock is obtained when an object is updated
* or inserted. This lock mode is for internal use only and is
* not a valid mode for <tt>load()</tt> or <tt>lock()</tt> (both
* of which throw exceptions if WRITE is specified).
*/
public static final LockMode WRITE = new LockMode(10, "WRITE");
/**
* Similiar to {@link #UPGRADE} except that, for versioned entities,
* it results in a forced version increment.
*/
public static final LockMode FORCE = new LockMode( 15, "FORCE" );
static {
INSTANCES.put( NONE.name, NONE );
INSTANCES.put( READ.name, READ );
INSTANCES.put( UPGRADE.name, UPGRADE );
INSTANCES.put( UPGRADE_NOWAIT.name, UPGRADE_NOWAIT );
INSTANCES.put( WRITE.name, WRITE );
INSTANCES.put( FORCE.name, FORCE );
}
private Object readResolve() {
return parse( name );
}
public static LockMode parse(String name) {
return ( LockMode ) INSTANCES.get(name);
}
}
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