org.glassfish.pfl.dynamic.copyobject.impl.ClassCopierBase Maven / Gradle / Ivy
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package org.glassfish.pfl.dynamic.copyobject.impl ;
import org.glassfish.pfl.dynamic.copyobject.spi.ReflectiveCopyException;
import java.util.HashMap;
import java.util.Map;
/** A convenient base class for making ClassCopier types.
* This takes care of checking oldToNew and updating oldToNew
* when an actual copy is made. All subclasses must override
* createCopy, which allocates a new result. In some simple
* cases, this is all that is needed. In the more complex
* cases, doCopy must also be overridden to make the actual copy.
*/
public abstract class ClassCopierBase implements ClassCopier {
private String name ;
private boolean isReflective ;
/** Pass a name here that can be used for toString, hashCode, and equals.
* All different ClassCopier classes derived from this base should
* have unique names.
*/
protected ClassCopierBase( String name )
{
this( name, false ) ;
}
protected ClassCopierBase( String name, boolean isReflective )
{
this.name = name ;
this.isReflective = isReflective ;
}
// Implement toString() and equals() as debugging and testing aids.
// Implement hashCode() to satisfy the general contracts of equals and
// hash.
@Override
public final String toString()
{
return "ClassCopier[" + name + "]" ;
}
@Override
public final int hashCode()
{
return name.hashCode() ;
}
@Override
public final boolean equals( Object obj )
{
if (this == obj) {
return true;
}
if (!(obj instanceof ClassCopierBase)) {
return false;
}
ClassCopierBase other = (ClassCopierBase)obj ;
return name.equals( other.name ) && (isReflective == other.isReflective) ;
}
/** Make the actual copy of source, using oldToNew to preserve aliasing.
* This first checks to see whether source has been previously copied.
* If so, the value obtained from oldToNew is returned. Otherwise,
*
* - createCopy( source ) is called to create a new copy of source.
*
- The new copy is placed in oldToNew with source as its key.
*
- doCopy is called to complete the copy.
*
* This split into two phases isolates all subclasses from the need to
* update oldToNew. It accommodates simple cases (arrays of primitives
* for example) that only need to define createCopy, as well as more complex
* case (general objects) that must first create the copy, update oldToNew,
* and then do the copy, as otherwise self-references would cause
* infinite recursion.
*/
@Override
public final Object copy(Map oldToNew, Object source) throws ReflectiveCopyException {
Object result = oldToNew.get(source);
if (result == null) {
result = doSpecialCaseCopy(oldToNew, source);
}
if (result == null) {
result = doByFieldCopy(oldToNew, source);
}
return result;
}
/**
* Sometimes the internal representation of an object will be violated by our field-by-field copy. This method
* handles those special cases. It suggests that there may be a basic problem with our code logic.
* @param oldToNew a map of already copied objects and their corresponding copies.
* @param source the object to copy.
*/
private Object doSpecialCaseCopy(Map oldToNew, Object source) {
Object result = null;
if (isEmptyHashMap(source))
result = cloneEmptyHashMap();
if (result != null)
oldToNew.put(source, result);
return result;
}
/**
* As of JDK 1.7-40, the JDK relies on the HashMap#table field being identical to a constant. That will not be
* true if we invoke #doByFieldCopy to copy it, so we need special processing.
* @param source the object to copy.
*/
private boolean isEmptyHashMap(Object source) {
return source instanceof HashMap && ((HashMap) source).isEmpty();
}
private HashMap cloneEmptyHashMap() {
return new HashMap();
}
private Object doByFieldCopy(Map oldToNew, Object source) {
Object result;
try {
result = createCopy(source);
oldToNew.put(source, result);
result = doCopy(oldToNew, source, result);
} catch (StackOverflowError ex) {
throw Exceptions.self.stackOverflow(source, ex);
}
return result;
}
@Override
public boolean isReflectiveClassCopier()
{
return isReflective ;
}
/** Create a copy of source. The copy may or may not be fully
* initialized. This method must always be overridden in a
* subclass.
*/
protected abstract Object createCopy(
Object source ) throws ReflectiveCopyException ;
/** Do the copying of data from source to result.
* This just returns the result by default, but it may be overrideden
* in a subclass. When this method completes, result must be fully
* initialized.
*/
protected Object doCopy( Map oldToNew,
Object source, Object result ) throws ReflectiveCopyException
{
return result ;
}
}