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/*
* ============LICENSE_START=======================================================
* feature-server-pool
* ================================================================================
* Copyright (C) 2020 AT&T Intellectual Property. All rights reserved.
* ================================================================================
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
* ============LICENSE_END=========================================================
*/
package org.onap.policy.drools.serverpool;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;
import java.util.Properties;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Function;
import lombok.AllArgsConstructor;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* This class supports the lookup of keywords from objects within Drools
* sessions. It maps the class of the object into an object implementing
* the 'Keyword.Lookup' interface. At present, this requires writing
* special code for each class that can exist in a Drools session that is
* assignable and relocatable via a bucket. In theory, it would be possible
* to populate this table through properties, which would use the reflective
* interface, and indicate the methods and fields to use to do this lookup.
*/
public class Keyword {
private static Logger logger = LoggerFactory.getLogger(Keyword.class);
// this table can be used to map an object class into the method
// to invoke to do the lookup
private static ConcurrentHashMap<Class<?>, Lookup> classToLookup =
new ConcurrentHashMap<>();
// this is a pre-defined 'Lookup' instance that always returns 'null'
private static Lookup nullLookup = (Object obj) -> (String) null;
/**
* This method takes the object's class, looks it up in the 'classToLookup'
* table, and then performs the lookup to get the keyword. When a direct
* lookup on a class fails, it will attempt to find a match using inheritance
* rules -- if an appropriate match is found, the 'classToLookup' table is
* updated, so it will be easier next time. If no match is found, the table
* is also updated, but the 'value' will be 'nullLookup'.
*
* @param obj object to to the lookup on
* @return a String keyword, if found; 'null' if not
*/
public static String lookupKeyword(Object obj) {
Lookup lu = classToLookup.get(obj.getClass());
if (lu != null) {
return lu.getKeyword(obj);
}
// no entry for this class yet --
// try to locate a matching entry using 'inheritance' rules
Class<?> thisClass = obj.getClass();
Class<?> matchingClass = null;
for (Map.Entry<Class<?>, Lookup> entry : classToLookup.entrySet()) {
if (entry.getKey().isAssignableFrom(thisClass)
&& (matchingClass == null
|| matchingClass.isAssignableFrom(entry.getKey()))) {
// we have a first match, or a more specific match
matchingClass = entry.getKey();
lu = entry.getValue();
}
}
/*
* whether we found a match or not, update the table accordingly
* no match found -- see if the 'keyword.<CLASS-NAME>.lookup'
* properties can provide a solution.
*/
if (lu == null && (lu = buildReflectiveLookup(thisClass)) == null) {
lu = nullLookup;
}
// update table
classToLookup.put(thisClass, lu);
return lu.getKeyword(obj);
}
/**
* explicitly place an entry in the table.
*
* @param clazz the class to do the lookup on
* @param handler an instance implementing the 'Lookup' interface,
* can handle instances of type 'clazz'
*/
public static void setLookupHandler(Class<?> clazz, Lookup handler) {
classToLookup.put(clazz, handler);
}
/* ============================================================ */
/**
* These are the interface that must be implemented by objects in the
* 'classToLookup' table.
*/
public interface Lookup {
/**
* Map the object into a keyword string.
*
* @param obj the object to lookup, which should be an instance of the
* associated class in the 'classToLookup' table
* @return the keyword, if found; 'null' if not
*/
public String getKeyword(Object obj);
}
/* ============================================================ */
// this table maps class name to a sequence of method calls and field
// references, based upon 'keyword.<CLASS-NAME>.lookup' entries found
// in the property list
private static Map<String, String> classNameToSequence = null;
static final String KEYWORD_PROPERTY_START = "keyword.";
static final String KEYWORD_PROPERTY_END = ".lookup";
/**
* Attempt to build a 'Lookup' instance for a particular class based upon
* properties.
*
* @param clazz the class to build an entry for
* @return a 'Lookup' instance to do the lookup, or 'null' if one can't
* be generated from the available properties
*/
private static synchronized Lookup buildReflectiveLookup(Class<?> clazz) {
if (classNameToSequence == null) {
classNameToSequence = new HashMap<>();
Properties prop = ServerPoolProperties.getProperties();
/*
* iterate over all of the properties, picking out those
* that match the name 'keyword.<CLASS-NAME>.lookup'
*/
for (String name : prop.stringPropertyNames()) {
if (name.startsWith(KEYWORD_PROPERTY_START)
&& name.endsWith(KEYWORD_PROPERTY_END)) {
// this property matches -- locate the '<CLASS-NAME>' part
int beginIndex = KEYWORD_PROPERTY_START.length();
int endIndex = name.length()
- KEYWORD_PROPERTY_END.length();
if (beginIndex < endIndex) {
// add it to the table
classNameToSequence.put(name.substring(beginIndex, endIndex),
prop.getProperty(name));
}
}
}
}
Class<?> keyClass = buildReflectiveLookup_findKeyClass(clazz);
if (keyClass == null) {
// no matching class name found
return null;
}
return buildReflectiveLookup_build(clazz, keyClass);
}
/**
* Look for the "best match" for class 'clazz' in the hash table.
* First, look for the name of 'clazz' itself, followed by all of
* interfaces. If no match is found, repeat with the superclass,
* and all the way up the superclass chain.
*/
private static Class<?> buildReflectiveLookup_findKeyClass(Class<?> clazz) {
Class<?> keyClass = null;
for (Class<?> cl = clazz; cl != null; cl = cl.getSuperclass()) {
if (classNameToSequence.containsKey(cl.getName())) {
// matches the class
keyClass = cl;
break;
}
for (Class<?> intf : cl.getInterfaces()) {
if (classNameToSequence.containsKey(intf.getName())) {
// matches one of the interfaces
keyClass = intf;
break;
}
// interface can have superclass
for (Class<?> cla = clazz; cla != null; cla = intf.getSuperclass()) {
if (classNameToSequence.containsKey(cla.getName())) {
// matches the class
keyClass = cla;
break;
}
}
}
if (keyClass != null) {
break;
}
}
return keyClass;
}
private static Lookup buildReflectiveLookup_build(Class<?> clazz, Class<?> keyClass) {
// we found a matching key in the table -- now, process the values
Class<?> currentClass = keyClass;
/*
* there may potentially be a chain of entries if multiple
* field and/or method calls are in the sequence -- this is the first
*/
ReflectiveLookup first = null;
// this is the last entry in the list
ReflectiveLookup last = null;
/*
* split the value into segments, where each segment has the form
* 'FIELD-NAME' or 'METHOD-NAME()', with an optional ':CONVERSION'
* at the end
*/
String sequence = classNameToSequence.get(keyClass.getName());
ConversionFunctionLookup conversionFunctionLookup = null;
int index = sequence.indexOf(':');
if (index >= 0) {
// conversion function specified
conversionFunctionLookup =
new ConversionFunctionLookup(sequence.substring(index + 1));
sequence = sequence.substring(0, index);
}
for (String segment : sequence.split("\\.")) {
ReflectiveLookup current = null;
ReflectiveOperationException error = null;
try {
if (segment.endsWith("()")) {
// this segment is a method lookup
current = new MethodLookup(currentClass,
segment.substring(0, segment.length() - 2));
} else {
// this segment is a field lookup
current = new FieldLookup(currentClass, segment);
}
} catch (ReflectiveOperationException e) {
// presumably the field or method does not exist in this class
error = e;
}
if (current == null) {
logger.error("Keyword.buildReflectiveLookup: build error "
+ "(class={},value={},segment={})",
clazz.getName(),
classNameToSequence.get(keyClass.getName()),
segment,
error);
return null;
}
// if we reach this point, we processed this segment successfully
currentClass = current.nextClass();
if (first == null) {
// the initial segment
first = current;
} else {
// link to the most recently created segment
last.next = current;
}
// update most recently created segment
last = current;
}
// add optional conversion function ('null' if it doesn't exist)
last.next = conversionFunctionLookup;
// successful - return the first 'Lookup' instance in the chain
return first;
}
/* ============================================================ */
/**
* Abstract superclass of 'FieldLookup' and 'MethodLookup'.
*/
private abstract static class ReflectiveLookup implements Lookup {
// link to the next 'Lookup' instance in the chain
Lookup next = null;
/**
* Return the next 'class' instance.
*
* @return the class associated with the return value of the
* field or method lookup
*/
abstract Class<?> nextClass();
}
/* ============================================================ */
/**
* This class is used to do a field lookup.
*/
private static class FieldLookup extends ReflectiveLookup {
// the reflective 'Field' instance associated with this lookup
Field field;
/**
* Constructor.
*
* @param clazz the 'class' we are doing the field lookup on
* @param segment a segment from the property value, which is just the
* field name
*/
FieldLookup(Class<?> clazz, String segment) throws NoSuchFieldException {
field = clazz.getField(segment);
}
/* ****************************** */
/* 'ReflectiveLookup' interface */
/* ****************************** */
/**
* {@inheritDoc}
*/
@Override
Class<?> nextClass() {
return field.getType();
}
/* ******************** */
/* 'Lookup' interface */
/* ******************** */
/**
* {@inheritDoc}
*/
@Override
public String getKeyword(Object obj) {
try {
// do the field lookup
Object rval = field.get(obj);
if (rval == null) {
return null;
}
// If there is no 'next' entry specified, this value is the
// keyword. Otherwise, move on to the next 'Lookup' entry in
// the chain.
return next == null ? rval.toString() : next.getKeyword(rval);
} catch (Exception e) {
logger.error("Keyword.FieldLookup error: field={}",
field, e);
return null;
}
}
}
/* ============================================================ */
/**
* This class is used to do a method call on the target object.
*/
private static class MethodLookup extends ReflectiveLookup {
// the reflective 'Method' instance associated with this lookup
Method method;
/**
* Constructor.
*
* @param clazz the 'class' we are doing the method lookup on
* @param name a method name extracted from a segment from the
* property value, which is the
*/
MethodLookup(Class<?> clazz, String name) throws NoSuchMethodException {
method = clazz.getMethod(name);
}
/*==============================*/
/* 'ReflectiveLookup' interface */
/*==============================*/
/**
* {@inheritDoc}
*/
@Override
Class<?> nextClass() {
return method.getReturnType();
}
/*====================*/
/* 'Lookup' interface */
/*====================*/
/**
* {@inheritDoc}
*/
@Override
public String getKeyword(Object obj) {
try {
// do the method call
Object rval = method.invoke(obj);
if (rval == null) {
return null;
}
// If there is no 'next' entry specified, this value is the
// keyword. Otherwise, move on to the next 'Lookup' entry in
// the chain.
return next == null ? rval.toString() : next.getKeyword(rval);
} catch (Exception e) {
logger.error("Keyword.MethodLookup error: method={}",
method, e);
return null;
}
}
}
/* ============================================================ */
/*
* Support for named "conversion functions", which take an input keyword,
* and return a possibly different keyword derived from it. The initial
* need is to take a string which consists of a UUID and a suffix, and
* return the base UUID.
*/
// used to lookup optional conversion functions
private static Map<String, Function<String, String>> conversionFunction =
new ConcurrentHashMap<>();
// conversion function 'uuid':
// truncate strings to 36 characters(uuid length)
static final int UUID_LENGTH = 36;
static {
conversionFunction.put("uuid", value -> {
// truncate strings to 36 characters
return value != null && value.length() > UUID_LENGTH
? value.substring(0, UUID_LENGTH) : value;
});
}
/**
* Add a conversion function.
*
* @param name the conversion function name
* @param function the object that does the transformation
*/
public static void addConversionFunction(String name, Function<String, String> function) {
conversionFunction.put(name, function);
}
/**
* Apply a named conversion function to a keyword.
*
* @param inputKeyword this is the keyword extracted from a message or object
* @param functionName this is the name of the conversion function to apply
* (if 'null', no conversion is done)
* @return the converted keyword
*/
public static String convertKeyword(String inputKeyword, String functionName) {
if (functionName == null || inputKeyword == null) {
// don't do any conversion -- just return the input keyword
return inputKeyword;
}
// look up the function
Function<String, String> function = conversionFunction.get(functionName);
if (function == null) {
logger.error("{}: conversion function not found", functionName);
return null;
}
// call the conversion function, and return the value
return function.apply(inputKeyword);
}
/**
* This class is used to invoke a conversion function.
*/
@AllArgsConstructor
private static class ConversionFunctionLookup implements Lookup {
// the conversion function name
private final String functionName;
/**
* {@inheritDoc}
*/
@Override
public String getKeyword(Object obj) {
return obj == null ? null : convertKeyword(obj.toString(), functionName);
}
}
}
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