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| java.lang.Object
 org.apache.harmony.security.asn1.ASN1Type
org.apache.harmony.security.asn1.ASN1Choice
All known Subclasses: org.apache.harmony.jndi.provider.ldap.asn1.ASN1ChoiceWrap,
| ASN1Choice | | abstract public class ASN1Choice extends ASN1Type (Code) | | This abstract class represents ASN.1 Choice type.
To implement custom ASN.1 choice type an application class
must provide implementation for the following methods:
getIndex()
getObjectToEncode()
There are two ways to implement custom ASN.1 choice type:
with application class that represents ASN.1 custom choice type or without.
The key point is how a value of choice type is stored by application classes.
For example, let's consider the following ASN.1 notations
(see http://www.ietf.org/rfc/rfc3280.txt)
Time ::= CHOICE {
utcTime UTCTime,
generalTime GeneralizedTime
}
Validity ::= SEQUENCE {
notBefore Time,
notAfter Time
}
1)First approach:
No application class to represent ASN.1 Time notation
The Time notation is a choice of different time formats: UTC and Generalized.
Both of them are mapped to java.util.Date object, so an application
class that represents ASN.1 Validity notation may keep values
as Date objects.
So a custom ASN.1 Time choice type should map its notation to Date object.
class Time {
// custom ASN.1 choice class: maps Time to is notation
public static final ASN1Choice asn1 = new ASN1Choice(new ASN1Type[] {
ASN1GeneralizedTime.asn1, ASN1UTCTime.asn1 }) {
public int getIndex(java.lang.Object object) {
return 0; // always encode as ASN1GeneralizedTime
}
public Object getObjectToEncode(Object object) {
// A value to be encoded value is a Date object
// pass it to custom time class
return object;
}
};
}
class Validity {
private Date notBefore; // choice as Date
private Date notAfter; // choice as Date
... // constructors and other methods go here
// custom ASN.1 sequence class: maps Validity class to is notation
public static final ASN1Sequence ASN1
= new ASN1Sequence(new ASN1Type[] {Time.asn1, Time.asn1 }) {
protected Object getObject(Object[] values) {
// ASN.1 Time choice passed Data object - use it
return new Validity((Date) values[0], (Date) values[1]);
}
protected void getValues(Object object, Object[] values) {
Validity validity = (Validity) object;
// pass Date objects to ASN.1 Time choice
values[0] = validity.notBefore;
values[1] = validity.notAfter;
}
}
}
2)Second approach:
There is an application class to represent ASN.1 Time notation
If it is a matter what time format should be used to decode/encode
Date objects a class to represent ASN.1 Time notation must be created.
For example,
class Time {
private Date utcTime;
private Date gTime;
... // constructors and other methods go here
// custom ASN.1 choice class: maps Time to is notation
public static final ASN1Choice asn1 = new ASN1Choice(new ASN1Type[] {
ASN1GeneralizedTime.asn1, ASN1UTCTime.asn1 }) {
public Object getDecodedObject(BerInputStream in) {
// create Time object to pass as decoded value
Time time = new Time();
if (in.choiceIndex==0) {
// we decoded GeneralizedTime
// store decoded Date value in corresponding field
time.gTime = in.content;
// return it
return time;
} else {
// we decoded UTCTime
// store decoded Date value in corresponding field
time.utcTime = in.content;
// return it
return time;
}
}
public int getIndex(java.lang.Object object) {
Time time = (Time)object;
if(time.utcTime!=null){
// encode Date as UTCTime
return 1;
} else {
// otherwise encode Date as GeneralizedTime
return 0;
}
}
public Object getObjectToEncode(Object object) {
Time time = (Time)object;
if(time.utcTime!=null){
// encode Date as UTCTime
return 1;
} else {
// otherwise encode Date as GeneralizedTime
return 0;
}
}
};
}
So now Validity class must keep all values in Time object
and its custom ASN.1 sequence class must handle this class of objects
class Validity {
private Time notBefore; // now it is a Time!!!
private Time notAfter; // now it is a Time!!!
... // constructors and other methods go here
// custom ASN.1 sequence class: maps Validity class to is notation
public static final ASN1Sequence ASN1
= new ASN1Sequence(new ASN1Type[] {Time.asn1, Time.asn1 }) {
protected Object getObject(Object[] values) {
// We've gotten Time objects here !!!
return new Validity((Time) values[0], (Time) values[1]);
}
protected void getValues(Object object, Object[] values) {
Validity validity = (Validity) object;
// pass Time objects to ASN.1 Time choice
values[0] = validity.notBefore;
values[1] = validity.notAfter;
}
}
}
See Also: http://asn1.elibel.tm.fr/en/standards/index.htm |
| ASN1Choice | | public ASN1Choice(ASN1Type[] type)(Code) | | Constructs ASN.1 choice type.
Parameters:
type - -an array of one or more ASN.1 type alternatives.
throws:
IllegalArgumentException - -type parameter is invalid |
| checkTag | | final public boolean checkTag(int identifier)(Code) | | Tests whether one of choice alternatives has the same identifier or not.
Parameters:
identifier - -ASN.1 identifier to be verified - true if one of choice alternatives has the same identifier,otherwise false; |
| getIndex | | abstract public int getIndex(Object object)(Code) | | TODO Put method description here
Parameters:
object - - an object to be encoded |
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