https://github.com/spring-projects/spring-framework: Spring Beans (Spring IO)
  • Juergen Hoeller 
/*
 * Copyright 2002-2018 the original author or authors.
 *
 * 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
 *
 *      https://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 org.springframework.beans;

import java.beans.PropertyDescriptor;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import org.springframework.util.ObjectUtils;
import org.springframework.util.ReflectionUtils;
import org.springframework.util.StringUtils;


Helper class for calculating property matches, according to a configurable
distance. Provide the list of potential matches and an easy way to generate
an error message. Works for both java bean properties and fields.

Mainly for use within the framework and in particular the binding facility.

Author:Alef Arendsen, Arjen Poutsma, Juergen Hoeller, Stephane Nicoll
See Also:
Since:2.0
/**
 * Helper class for calculating property matches, according to a configurable
 * distance. Provide the list of potential matches and an easy way to generate
 * an error message. Works for both java bean properties and fields.
 *
 * <p>Mainly for use within the framework and in particular the binding facility.
 *
 * @author Alef Arendsen
 * @author Arjen Poutsma
 * @author Juergen Hoeller
 * @author Stephane Nicoll
 * @since 2.0
 * @see #forProperty(String, Class)
 * @see #forField(String, Class)
 */
public abstract class PropertyMatches {

	
Default maximum property distance: 2. 
/** Default maximum property distance: 2. */
	public static final int DEFAULT_MAX_DISTANCE = 2;


	// Static factory methods

	
Create PropertyMatches for the given bean property.

Params:
  • propertyName – the name of the property to find possible matches for
  • beanClass – the bean class to search for matches
/**
	 * Create PropertyMatches for the given bean property.
	 * @param propertyName the name of the property to find possible matches for
	 * @param beanClass the bean class to search for matches
	 */
	public static PropertyMatches forProperty(String propertyName, Class<?> beanClass) {
		return forProperty(propertyName, beanClass, DEFAULT_MAX_DISTANCE);
	}

	
Create PropertyMatches for the given bean property.

Params:
  • propertyName – the name of the property to find possible matches for
  • beanClass – the bean class to search for matches
  • maxDistance – the maximum property distance allowed for matches
/**
	 * Create PropertyMatches for the given bean property.
	 * @param propertyName the name of the property to find possible matches for
	 * @param beanClass the bean class to search for matches
	 * @param maxDistance the maximum property distance allowed for matches
	 */
	public static PropertyMatches forProperty(String propertyName, Class<?> beanClass, int maxDistance) {
		return new BeanPropertyMatches(propertyName, beanClass, maxDistance);
	}

	
Create PropertyMatches for the given field property.

Params:
  • propertyName – the name of the field to find possible matches for
  • beanClass – the bean class to search for matches
/**
	 * Create PropertyMatches for the given field property.
	 * @param propertyName the name of the field to find possible matches for
	 * @param beanClass the bean class to search for matches
	 */
	public static PropertyMatches forField(String propertyName, Class<?> beanClass) {
		return forField(propertyName, beanClass, DEFAULT_MAX_DISTANCE);
	}

	
Create PropertyMatches for the given field property.

Params:
  • propertyName – the name of the field to find possible matches for
  • beanClass – the bean class to search for matches
  • maxDistance – the maximum property distance allowed for matches
/**
	 * Create PropertyMatches for the given field property.
	 * @param propertyName the name of the field to find possible matches for
	 * @param beanClass the bean class to search for matches
	 * @param maxDistance the maximum property distance allowed for matches
	 */
	public static PropertyMatches forField(String propertyName, Class<?> beanClass, int maxDistance) {
		return new FieldPropertyMatches(propertyName, beanClass, maxDistance);
	}


	// Instance state

	private final String propertyName;

	private final String[] possibleMatches;


	
Create a new PropertyMatches instance for the given property and possible matches.

/**
	 * Create a new PropertyMatches instance for the given property and possible matches.
	 */
	private PropertyMatches(String propertyName, String[] possibleMatches) {
		this.propertyName = propertyName;
		this.possibleMatches = possibleMatches;
	}


	
Return the name of the requested property.

/**
	 * Return the name of the requested property.
	 */
	public String getPropertyName() {
		return this.propertyName;
	}

	
Return the calculated possible matches.

/**
	 * Return the calculated possible matches.
	 */
	public String[] getPossibleMatches() {
		return this.possibleMatches;
	}

	
Build an error message for the given invalid property name,
indicating the possible property matches.

/**
	 * Build an error message for the given invalid property name,
	 * indicating the possible property matches.
	 */
	public abstract String buildErrorMessage();


	// Implementation support for subclasses

	protected void appendHintMessage(StringBuilder msg) {
		msg.append("Did you mean ");
		for (int i = 0; i < this.possibleMatches.length; i++) {
			msg.append('\'');
			msg.append(this.possibleMatches[i]);
			if (i < this.possibleMatches.length - 2) {
				msg.append("', ");
			}
			else if (i == this.possibleMatches.length - 2) {
				msg.append("', or ");
			}
		}
		msg.append("'?");
	}

	
Calculate the distance between the given two Strings
according to the Levenshtein algorithm.

Params:
  • s1 – the first String
  • s2 – the second String
Returns:the distance value
/**
	 * Calculate the distance between the given two Strings
	 * according to the Levenshtein algorithm.
	 * @param s1 the first String
	 * @param s2 the second String
	 * @return the distance value
	 */
	private static int calculateStringDistance(String s1, String s2) {
		if (s1.isEmpty()) {
			return s2.length();
		}
		if (s2.isEmpty()) {
			return s1.length();
		}

		int[][] d = new int[s1.length() + 1][s2.length() + 1];
		for (int i = 0; i <= s1.length(); i++) {
			d[i][0] = i;
		}
		for (int j = 0; j <= s2.length(); j++) {
			d[0][j] = j;
		}

		for (int i = 1; i <= s1.length(); i++) {
			char c1 = s1.charAt(i - 1);
			for (int j = 1; j <= s2.length(); j++) {
				int cost;
				char c2 = s2.charAt(j - 1);
				if (c1 == c2) {
					cost = 0;
				}
				else {
					cost = 1;
				}
				d[i][j] = Math.min(Math.min(d[i - 1][j] + 1, d[i][j - 1] + 1), d[i - 1][j - 1] + cost);
			}
		}

		return d[s1.length()][s2.length()];
	}


	// Concrete subclasses

	private static class BeanPropertyMatches extends PropertyMatches {

		public BeanPropertyMatches(String propertyName, Class<?> beanClass, int maxDistance) {
			super(propertyName,
					calculateMatches(propertyName, BeanUtils.getPropertyDescriptors(beanClass), maxDistance));
		}

		
Generate possible property alternatives for the given property and class. Internally uses the getStringDistance method, which in turn uses the Levenshtein algorithm to determine the distance between two Strings. 
Params:
  • descriptors – the JavaBeans property descriptors to search
  • maxDistance – the maximum distance to accept
/**
		 * Generate possible property alternatives for the given property and class.
		 * Internally uses the {@code getStringDistance} method, which in turn uses
		 * the Levenshtein algorithm to determine the distance between two Strings.
		 * @param descriptors the JavaBeans property descriptors to search
		 * @param maxDistance the maximum distance to accept
		 */
		private static String[] calculateMatches(String name, PropertyDescriptor[] descriptors, int maxDistance) {
			List<String> candidates = new ArrayList<>();
			for (PropertyDescriptor pd : descriptors) {
				if (pd.getWriteMethod() != null) {
					String possibleAlternative = pd.getName();
					if (calculateStringDistance(name, possibleAlternative) <= maxDistance) {
						candidates.add(possibleAlternative);
					}
				}
			}
			Collections.sort(candidates);
			return StringUtils.toStringArray(candidates);
		}

		@Override
		public String buildErrorMessage() {
			StringBuilder msg = new StringBuilder(160);
			msg.append("Bean property '").append(getPropertyName()).append(
					"' is not writable or has an invalid setter method. ");
			if (!ObjectUtils.isEmpty(getPossibleMatches())) {
				appendHintMessage(msg);
			}
			else {
				msg.append("Does the parameter type of the setter match the return type of the getter?");
			}
			return msg.toString();
		}
	}


	private static class FieldPropertyMatches extends PropertyMatches {

		public FieldPropertyMatches(String propertyName, Class<?> beanClass, int maxDistance) {
			super(propertyName, calculateMatches(propertyName, beanClass, maxDistance));
		}

		private static String[] calculateMatches(final String name, Class<?> clazz, final int maxDistance) {
			final List<String> candidates = new ArrayList<>();
			ReflectionUtils.doWithFields(clazz, field -> {
				String possibleAlternative = field.getName();
				if (calculateStringDistance(name, possibleAlternative) <= maxDistance) {
					candidates.add(possibleAlternative);
				}
			});
			Collections.sort(candidates);
			return StringUtils.toStringArray(candidates);
		}

		@Override
		public String buildErrorMessage() {
			StringBuilder msg = new StringBuilder(80);
			msg.append("Bean property '").append(getPropertyName()).append("' has no matching field.");
			if (!ObjectUtils.isEmpty(getPossibleMatches())) {
				msg.append(' ');
				appendHintMessage(msg);
			}
			return msg.toString();
		}
	}

}