assert.java

一个关于Spring框架的示例应用程序,简单使用,可以参考.

/*
 * Copyright 2002-2004 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
 *
 * 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 org.springframework.util;

import java.util.Collection;
import java.util.Map;

/**
 * Assert utility class that assists in validating arguments. Useful for
 * identifying programmer errors early and obviously at runtime.
 *
 * <p>For example, if the contract of a public method states it does not allow null
 * arguments, Assert can be used to validate that contract. Doing this clearly
 * indicates a contract violation when it occurs and protects the class's
 * invariants.
 *
 * <p>Typically used to validate method arguments rather than configuration
 * properties, to check for cases that are usually programmer errors rather than
 * configuration errors. In contrast to config initialization code, there is
 * usally no point in falling back to defaults in such methods.
 *
 * <p>This class is similar to JUnit's assertion library. If an argument value is
 * deemed invalid, an IllegalArgumentException is thrown. For example:
 *
 * <pre>
 * Assert.notNull(clazz, "The class must not be null");
 * Assert.isTrue(i > 0, "The value must be greater than zero");</pre>
 *
 * Mainly for internal use within the framework; consider Jakarta's Commons Lang
 * >= 2.0 for a more comprehensive suite of assertion utilities.
 * @author Keith Donald
 * @author Juergen Hoeller
 * @author Colin Sampaleanu
 * @since 1.1.2
 */
public abstract class Assert {

	/**
	 * Assert a boolean expression, throwing
	 * <code>IllegalArgumentException</code> if the test result is
	 * <code>false</code>.
	 * <pre>
	 * Assert.isTrue(i > 0, "The value must be greater than zero");</pre>
	 * @param expression a boolean expression
	 * @param message the exception message to use if the assertion fails
	 * @throws IllegalArgumentException if expression is <code>false</code>
	 */
	public static void isTrue(boolean expression, String message) {
		if (!expression) {
			throw new IllegalArgumentException(message);
		}
	}

	/**
	 * Assert a boolean expression, throwing
	 * <code>IllegalArgumentException</code> if the test result is
	 * <code>false</code>.
	 * <pre>
	 * Assert.isTrue(i > 0);</pre>
	 * @param expression a boolean expression
	 * @throws IllegalArgumentException if expression is <code>false</code>
	 */
	public static void isTrue(boolean expression) {
		isTrue(expression, "[Assertion failed] - this expression must be true");
	}

	/**
	 * Assert that an object is not null.
	 * <pre>
	 * Assert.notNull(clazz, "The class must not be null");</pre>
	 * @param object the object to check
	 * @param message the exception message to use if the assertion fails
	 * @throws IllegalArgumentException if the object is <code>null</code>
	 */
	public static void notNull(Object object, String message) {
		if (object == null) {
			throw new IllegalArgumentException(message);
		}
	}

	/**
	 * Assert that an object is not null.
	 * <pre>
	 * Assert.notNull(clazz);</pre>
	 * @param object the object to check
	 * @throws IllegalArgumentException if the object is <code>null</code>
	 */
	public static void notNull(Object object) {
		notNull(object, "[Assertion failed] - this argument is required; it cannot be null");
	}

	/**
	 * Assert that a string is not empty; that is, it must not be null and not empty.
	 * <pre>
	 * Assert.hasLength(name, "Name must not be empty");</pre>
	 * @param text the string to check
	 * @see StringUtils#hasLength
	 */
	public static void hasLength(String text, String message) {
		if (!StringUtils.hasLength(text)) {
			throw new IllegalArgumentException(message);
		}
	}

	/**
	 * Assert that a string is not empty; that is, it must not be null and not empty.
	 * <pre>
	 * Assert.hasLength(name);</pre>
	 * @param text the string to check
	 * @see StringUtils#hasLength
	 */
	public static void hasLength(String text) {
		hasLength(text, "[Assertion failed] - this string argument must have length; it cannot be null or empty");
	}

	/**
	 * Assert that a string has valid text content; that is, it must not be null
	 * and must contain at least one non-whitespace character.
	 * <pre>
	 * Assert.hasText(name, "Name must not be empty");</pre>
	 * @param text the string to check
	 * @see StringUtils#hasText
	 */
	public static void hasText(String text, String message) {
		if (!StringUtils.hasText(text)) {
			throw new IllegalArgumentException(message);
		}
	}

	/**
	 * Assert that a string has valid text content; that is, it must not be null
	 * and must contain at least one non-whitespace character.
	 * <pre>
	 * Assert.hasText(name, "Name must not be empty");</pre>
	 * @param text the string to check
	 * @see StringUtils#hasText
	 */
	public static void hasText(String text) {
		hasText(text,
				"[Assertion failed] - this string argument must have text; it cannot be null, empty, or blank");
	}

	/**
	 * Assert that an array has elements; that is, it must not be
	 * <code>null</code> and must have at least one element.
	 * <pre>
	 * Assert.notEmpty(array, "The array must have elements");</pre>
	 * @param array the array to check
	 * @param message the exception message to use if the assertion fails
	 * @throws IllegalArgumentException if the object array is <code>null</code> or has no elements
	 */
	public static void notEmpty(Object[] array, String message) {
		if (array == null || array.length == 0) {
			throw new IllegalArgumentException(message);
		}
	}

	/**
	 * Assert that an array has elements; that is, it must not be
	 * <code>null</code> and must have at least one element.
	 * <pre>
	 * Assert.notEmpty(array);</pre>
	 * @param array the array to check
	 * @throws IllegalArgumentException if the object array is <code>null</code> or has no elements
	 */
	public static void notEmpty(Object[] array) {
		notEmpty(array, "[Assertion failed] - this array must not be empty: it must contain at least 1 element");
	}

	/**
	 * Assert that a collection has elements; that is, it must not be
	 * <code>null</code> and must have at least one element.
	 * <pre>
	 * Assert.notEmpty(collection, "Collection must have elements");</pre>
	 * @param collection the collection to check
	 * @param message the exception message to use if the assertion fails
	 * @throws IllegalArgumentException if the collection is <code>null</code> or has no elements
	 */
	public static void notEmpty(Collection collection, String message) {
		if (collection == null || collection.isEmpty()) {
			throw new IllegalArgumentException(message);
		}
	}

	/**
	 * Assert that a collection has elements; that is, it must not be
	 * <code>null</code> and must have at least one element.
	 * <pre>
	 * Assert.notEmpty(collection, "Collection must have elements");</pre>
	 * @param collection the collection to check
	 * @throws IllegalArgumentException if the collection is <code>null</code> or has no elements
	 */
	public static void notEmpty(Collection collection) {
		notEmpty(collection,
				"[Assertion failed] - this collection must not be empty: it must contain at least 1 element");
	}

	/**
	 * Assert that a Map has entries; that is, it must not be <code>null</code>
	 * and must have at least one entry.
	 * <pre>
	 * Assert.notEmpty(map, "Map must have entries");</pre>
	 * @param map the map to check
	 * @param message the exception message to use if the assertion fails
	 * @throws IllegalArgumentException if the map is <code>null</code> or has no entries
	 */
	public static void notEmpty(Map map, String message) {
		if (map == null || map.isEmpty()) {
			throw new IllegalArgumentException(message);
		}
	}

	/**
	 * Assert that a Map has entries; that is, it must not be <code>null</code>
	 * and must have at least one entry.
	 * <pre>
	 * Assert.notEmpty(map);</pre>
	 * @param map the map to check
	 * @throws IllegalArgumentException if the map is <code>null</code> or has no entries
	 */
	public static void notEmpty(Map map) {
		notEmpty(map, "[Assertion failed] - this map must not be empty; it must contain at least one entry");
	}

	/**
	 * Assert that the provided object is an instance of the provided class.
	 * <pre>
	 * Assert.instanceOf(Foo.class, foo);</pre>
	 * @param clazz the required class
	 * @param obj the object to check
	 * @throws IllegalArgumentException if the object is not an instance of clazz
	 * @see Class#isInstance
	 */
	public static void isInstanceOf(Class clazz, Object obj) {
		isInstanceOf(clazz, obj, "");
	}

	/**
	 * Assert that the provided object is an instance of the provided class.
	 * <pre>
	 * Assert.instanceOf(Foo.class, foo);</pre>
	 * @param clazz the required class
	 * @param obj the object to check
	 * @param message a message which will be prepended to the message produced by
	 * the function itself, and which may be used to provide context. It should
	 * normally end in a ":" or ". " so that the function generate message looks
	 * ok when prepended to it.
	 * @throws IllegalArgumentException if the object is not an instance of clazz
	 * @see Class#isInstance
	 */
	public static void isInstanceOf(Class clazz, Object obj, String message) {
		Assert.notNull(clazz, "The clazz to perform the instanceof assertion cannot be null");
		Assert.isTrue(clazz.isInstance(obj), message +
				"Object of class '" + (obj != null ? obj.getClass().getName() : "[null]") +
				"' must be an instance of '" + clazz.getName() + "'");
	}


	/**
	 * Assert a boolean expression, throwing <code>IllegalStateException</code>
	 * if the test result is <code>false</code>. Call isTrue if you wish to
	 * throw IllegalArgumentException on an assertion failure.
	 * <pre>
	 * Assert.state(id == null, "The id property must not already be initialized");</pre>
	 * @param expression a boolean expression
	 * @param message the exception message to use if the assertion fails
	 * @throws IllegalStateException if expression is <code>false</code>
	 */
	public static void state(boolean expression, String message) {
		if (!expression) {
			throw new IllegalStateException(message);
		}
	}

	/**
	 * Assert a boolean expression, throwing <code>IllegalStateException</code>
	 * if the test result is <code>false</code>. Call isTrue if you wish to
	 * throw IllegalArgumentException on an assertion failure.
	 * <pre>
	 * Assert.state(id == null);</pre>
	 * @param expression a boolean expression
	 * @throws IllegalStateException if expression is <code>false</code>
	 */
	public static void state(boolean expression) {
		state(expression, "[Assertion failed] - this state invariant must be true");
	}

}