net.sf.ehcache.search.attribute.ReflectionAttributeExtractor Maven / Gradle / Ivy
/**
* Copyright Terracotta, Inc.
*
* 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.
*/
package net.sf.ehcache.search.attribute;
import java.io.Serializable;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import net.sf.ehcache.Element;
import net.sf.ehcache.config.InvalidConfigurationException;
/**
* Built-in search attribute extractor driven by method/value dotted expression
* chains.
*
* The expression chain must start with one of either "key", "value", or
* "element". From the starting object a chain of either method calls or field
* names follows. Method calls and field names can be freely mixed in the chain.
* Some examples:
*
* - "key.getName()" -- call getName() on the key object
*
- "value.person.getAge()" -- get the "person" field of the value object and call getAge() on it
*
- "element.toString()" -- call toString() on the element
*
* The method and field name portions of the expression are case sensitive
*
* @author teck
*/
public class ReflectionAttributeExtractor implements AttributeExtractor {
private static final String ELEMENT = "element";
private static final String KEY = "key";
private static final String VALUE = "value";
private final String expression;
private final Part[] parts;
private final StartType start;
/**
* Create a new ReflectionAttributeExtractor
*
* @param expression
*/
public ReflectionAttributeExtractor(String expression) throws InvalidConfigurationException {
String trimmed = expression.trim();
String[] tokens = trimmed.split("\\.");
if (tokens.length == 0) {
throw new InvalidConfigurationException("Invalid attribute expression: " + trimmed);
}
String startToken = tokens[0];
if (startToken.equalsIgnoreCase(ELEMENT)) {
start = StartType.ELEMENT;
} else if (startToken.equalsIgnoreCase(KEY)) {
start = StartType.KEY;
} else if (startToken.equalsIgnoreCase(VALUE)) {
start = StartType.VALUE;
} else {
throw new InvalidConfigurationException("Expression must start with either \"" + ELEMENT + "\", \"" + KEY + "\" or \"" + VALUE
+ "\": " + trimmed);
}
this.parts = parseExpression(tokens, trimmed);
this.expression = trimmed;
}
/**
* Evaluate the expression for the given element
*
* @return the attribute value
* @throws AttributeExtractorException if there is an error in evaluating the expression
*/
public Object attributeFor(Element e, String attributeName) throws AttributeExtractorException {
// NOTE: We can play all kinds of tricks of generating java classes and
// using Unsafe if needed
Object startObject;
switch (start) {
case ELEMENT: {
startObject = e;
break;
}
case KEY: {
startObject = e.getObjectKey();
break;
}
case VALUE: {
startObject = e.getObjectValue();
break;
}
default: {
throw new AssertionError(start.name());
}
}
Object rv = startObject;
for (Part part : parts) {
rv = part.eval(rv);
}
return rv;
}
private static Part[] parseExpression(String[] tokens, String expression) {
Part[] parts = new Part[tokens.length - 1];
for (int i = 1; i < tokens.length; i++) {
String token = tokens[i];
boolean method = false;
if (token.endsWith("()")) {
method = true;
token = token.substring(0, token.length() - 2);
}
verifyToken(token, expression);
if (method) {
parts[i - 1] = new MethodPart(token);
} else {
parts[i - 1] = new FieldPart(token);
}
}
return parts;
}
private static void verifyToken(String token, String expression) {
if (token.length() == 0) {
throw new InvalidConfigurationException("Empty element in expression: " + expression);
}
for (int i = 0; i < token.length(); i++) {
char c = token.charAt(i);
if (i == 0) {
if (!Character.isJavaIdentifierStart(c)) {
throw new InvalidConfigurationException("Invalid element (" + token + ") in expression: " + expression);
}
} else {
if (!Character.isJavaIdentifierPart(c)) {
throw new InvalidConfigurationException("Invalid element (" + token + ") in expression: " + expression);
}
}
}
}
/**
* The various types of the start of the expression
*/
private enum StartType {
ELEMENT, VALUE, KEY;
}
/**
* A part (method or field) of the expression
*/
private interface Part extends Serializable {
Object eval(Object target);
}
/**
* A field expression part
*/
private static class FieldPart implements Part {
private final String fieldName;
private transient volatile FieldRef cache;
public FieldPart(String field) {
this.fieldName = field;
}
public Object eval(Object target) {
if (target == null) {
throw new AttributeExtractorException("null reference encountered trying to read field " + fieldName);
}
Class c = target.getClass();
FieldRef ref = cache;
if (ref == null || ref.target != c) {
while (true) {
try {
Field field = c.getDeclaredField(fieldName);
field.setAccessible(true);
ref = new FieldRef(target.getClass(), field);
cache = ref;
break;
} catch (NoSuchFieldException e) {
c = c.getSuperclass();
if (c == null) {
throw new AttributeExtractorException("No such field named \"" + fieldName + "\" present in instance of "
+ target.getClass());
}
} catch (Exception e) {
throw new AttributeExtractorException(e);
}
}
}
try {
return ref.field.get(target);
} catch (Exception e) {
throw new AttributeExtractorException(e);
}
}
}
/**
* A reference to a resolved Field instance
*/
private static class FieldRef {
private final Class target;
private final Field field;
FieldRef(Class target, Field field) {
this.target = target;
this.field = field;
}
}
/**
* A reference to a resolved Method instance
*/
private static class MethodRef {
private final Method method;
private final Class target;
MethodRef(Class target, Method method) {
this.target = target;
this.method = method;
}
}
/**
* A method expression part
*/
private static class MethodPart implements Part {
private final String methodName;
private transient volatile MethodRef cache;
public MethodPart(String method) {
this.methodName = method;
}
public Object eval(Object target) {
if (target == null) {
throw new AttributeExtractorException("null reference encountered trying to call " + methodName + "()");
}
Class c = target.getClass();
MethodRef ref = cache;
if (ref == null || ref.target != c) {
while (true) {
try {
Method method = c.getDeclaredMethod(methodName);
method.setAccessible(true);
ref = new MethodRef(target.getClass(), method);
cache = ref;
break;
} catch (NoSuchMethodException e) {
c = c.getSuperclass();
if (c == null) {
throw new AttributeExtractorException("No such method named \"" + methodName + "\" present on instance of "
+ target.getClass());
}
} catch (Exception e) {
throw new AttributeExtractorException(e);
}
}
}
try {
return ref.method.invoke(target);
} catch (InvocationTargetException e) {
throw new AttributeExtractorException(e.getTargetException());
} catch (Exception e) {
throw new AttributeExtractorException(e);
}
}
}
}