spring在提供一个强大的应用开发框架的同时也提供了很多优秀的开发工具类，合理的运用这些工具，将有助于提高开发效率、增强代码质量。下面就最常用的Assert工具类，简要介绍一下它的用法。
Assert断言工具类，通常用于数据合法性检查。源码:
/* * Copyright 2002-2016 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;/** * Assertion utility class that assists in validating arguments. * *Useful for identifying programmer errors early and clearly at runtime. * *
For example, if the contract of a public method states it does not * allow {
@code null} arguments, { @code Assert} can be used to validate that * contract. Doing this clearly indicates a contract violation when it * occurs and protects the class's invariants. * *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 configuration initialization * code, there is usually no point in falling back to defaults in such methods. * *
This class is similar to JUnit's assertion library. If an argument value is * deemed invalid, an {
@link IllegalArgumentException} is thrown (typically). * For example: * ** Assert.notNull(clazz, "The class must not be null"); * Assert.isTrue(i > 0, "The value must be greater than zero");* *Mainly for internal use within the framework; consider * Apache's Commons Lang * for a more comprehensive suite of {
@code String} utilities. * * @author Keith Donald * @author Juergen Hoeller * @author Colin Sampaleanu * @author Rob Harrop * @author Sam Brannen * @since 1.1.2 */public abstract class Assert { /** * Assert a boolean expression, throwing { @code IllegalArgumentException} * if the test result is { @code false}. *Assert.isTrue(i > 0, "The value must be greater than zero");* @param expression a boolean expression * @param message the exception message to use if the assertion fails * @throws IllegalArgumentException if expression is { @code false} */ public static void isTrue(boolean expression, String message) { if (!expression) { throw new IllegalArgumentException(message); } } /** * Assert a boolean expression, throwing { @code IllegalArgumentException} * if the test result is { @code false}. *Assert.isTrue(i > 0);* @param expression a boolean expression * @throws IllegalArgumentException if expression is { @code false} */ public static void isTrue(boolean expression) { isTrue(expression, "[Assertion failed] - this expression must be true"); } /** * Assert that an object is { @code null} . *Assert.isNull(value, "The value must be null");* @param object the object to check * @param message the exception message to use if the assertion fails * @throws IllegalArgumentException if the object is not { @code null} */ public static void isNull(Object object, String message) { if (object != null) { throw new IllegalArgumentException(message); } } /** * Assert that an object is { @code null} . *Assert.isNull(value);* @param object the object to check * @throws IllegalArgumentException if the object is not { @code null} */ public static void isNull(Object object) { isNull(object, "[Assertion failed] - the object argument must be null"); } /** * Assert that an object is not { @code null} . *Assert.notNull(clazz, "The class must not be null");* @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} */ public static void notNull(Object object, String message) { if (object == null) { throw new IllegalArgumentException(message); } } /** * Assert that an object is not { @code null} . *Assert.notNull(clazz);* @param object the object to check * @throws IllegalArgumentException if the object is { @code null} */ public static void notNull(Object object) { notNull(object, "[Assertion failed] - this argument is required; it must not be null"); } /** * Assert that the given String is not empty; that is, * it must not be { @code null} and not the empty String. *Assert.hasLength(name, "Name must not be empty");* @param text the String to check * @param message the exception message to use if the assertion fails * @see StringUtils#hasLength * @throws IllegalArgumentException if the text is empty */ public static void hasLength(String text, String message) { if (!StringUtils.hasLength(text)) { throw new IllegalArgumentException(message); } } /** * Assert that the given String is not empty; that is, * it must not be { @code null} and not the empty String. *Assert.hasLength(name);* @param text the String to check * @see StringUtils#hasLength * @throws IllegalArgumentException if the text is empty */ public static void hasLength(String text) { hasLength(text, "[Assertion failed] - this String argument must have length; it must not be null or empty"); } /** * Assert that the given String has valid text content; that is, it must not * be { @code null} and must contain at least one non-whitespace character. *Assert.hasText(name, "'name' must not be empty");* @param text the String to check * @param message the exception message to use if the assertion fails * @see StringUtils#hasText * @throws IllegalArgumentException if the text does not contain valid text content */ public static void hasText(String text, String message) { if (!StringUtils.hasText(text)) { throw new IllegalArgumentException(message); } } /** * Assert that the given String has valid text content; that is, it must not * be { @code null} and must contain at least one non-whitespace character. *Assert.hasText(name, "'name' must not be empty");* @param text the String to check * @see StringUtils#hasText * @throws IllegalArgumentException if the text does not contain valid text content */ public static void hasText(String text) { hasText(text, "[Assertion failed] - this String argument must have text; it must not be null, empty, or blank"); } /** * Assert that the given text does not contain the given substring. *Assert.doesNotContain(name, "rod", "Name must not contain 'rod'");* @param textToSearch the text to search * @param substring the substring to find within the text * @param message the exception message to use if the assertion fails * @throws IllegalArgumentException if the text contains the substring */ public static void doesNotContain(String textToSearch, String substring, String message) { if (StringUtils.hasLength(textToSearch) && StringUtils.hasLength(substring) && textToSearch.contains(substring)) { throw new IllegalArgumentException(message); } } /** * Assert that the given text does not contain the given substring. *Assert.doesNotContain(name, "rod");* @param textToSearch the text to search * @param substring the substring to find within the text * @throws IllegalArgumentException if the text contains the substring */ public static void doesNotContain(String textToSearch, String substring) { doesNotContain(textToSearch, substring, "[Assertion failed] - this String argument must not contain the substring [" + substring + "]"); } /** * Assert that an array has elements; that is, it must not be * { @code null} and must have at least one element. *Assert.notEmpty(array, "The array must have elements");* @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} or has no elements */ public static void notEmpty(Object[] array, String message) { if (ObjectUtils.isEmpty(array)) { throw new IllegalArgumentException(message); } } /** * Assert that an array has elements; that is, it must not be * { @code null} and must have at least one element. *Assert.notEmpty(array);* @param array the array to check * @throws IllegalArgumentException if the object array is { @code null} 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 an array has no null elements. * Note: Does not complain if the array is empty! *Assert.noNullElements(array, "The array must have non-null elements");* @param array the array to check * @param message the exception message to use if the assertion fails * @throws IllegalArgumentException if the object array contains a { @code null} element */ public static void noNullElements(Object[] array, String message) { if (array != null) { for (Object element : array) { if (element == null) { throw new IllegalArgumentException(message); } } } } /** * Assert that an array has no null elements. * Note: Does not complain if the array is empty! *Assert.noNullElements(array);* @param array the array to check * @throws IllegalArgumentException if the object array contains a { @code null} element */ public static void noNullElements(Object[] array) { noNullElements(array, "[Assertion failed] - this array must not contain any null elements"); } /** * Assert that a collection has elements; that is, it must not be * { @code null} and must have at least one element. *Assert.notEmpty(collection, "Collection must have elements");* @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} or has no elements */ public static void notEmpty(Collection collection, String message) { if (CollectionUtils.isEmpty(collection)) { throw new IllegalArgumentException(message); } } /** * Assert that a collection has elements; that is, it must not be * { @code null} and must have at least one element. *Assert.notEmpty(collection, "Collection must have elements");* @param collection the collection to check * @throws IllegalArgumentException if the collection is { @code null} 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} * and must have at least one entry. *Assert.notEmpty(map, "Map must have entries");* @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} or has no entries */ public static void notEmpty(Map map, String message) { if (CollectionUtils.isEmpty(map)) { throw new IllegalArgumentException(message); } } /** * Assert that a Map has entries; that is, it must not be { @code null} * and must have at least one entry. *Assert.notEmpty(map);* @param map the map to check * @throws IllegalArgumentException if the map is { @code null} 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. *Assert.instanceOf(Foo.class, foo);* @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. *Assert.instanceOf(Foo.class, foo);* @param type the type to check against * @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 ":" or "." so that the generated message looks OK when * appended to it. * @throws IllegalArgumentException if the object is not an instance of clazz * @see Class#isInstance */ public static void isInstanceOf(Class type, Object obj, String message) { notNull(type, "Type to check against must not be null"); if (!type.isInstance(obj)) { throw new IllegalArgumentException( (StringUtils.hasLength(message) ? message + " " : "") + "Object of class [" + (obj != null ? obj.getClass().getName() : "null") + "] must be an instance of " + type); } } /** * Assert that { @code superType.isAssignableFrom(subType)} is { @code true}. *Assert.isAssignable(Number.class, myClass);* @param superType the super type to check * @param subType the sub type to check * @throws IllegalArgumentException if the classes are not assignable */ public static void isAssignable(Class superType, Class subType) { isAssignable(superType, subType, ""); } /** * Assert that { @code superType.isAssignableFrom(subType)} is { @code true}. *Assert.isAssignable(Number.class, myClass);* @param superType the super type to check against * @param subType the sub type 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 ":" or "." so that the generated message looks OK when * appended to it. * @throws IllegalArgumentException if the classes are not assignable */ public static void isAssignable(Class superType, Class subType, String message) { notNull(superType, "Type to check against must not be null"); if (subType == null || !superType.isAssignableFrom(subType)) { throw new IllegalArgumentException((StringUtils.hasLength(message) ? message + " " : "") + subType + " is not assignable to " + superType); } } /** * Assert a boolean expression, throwing { @code IllegalStateException} * if the test result is { @code false}. Call isTrue if you wish to * throw IllegalArgumentException on an assertion failure. *Assert.state(id == null, "The id property must not already be initialized");* @param expression a boolean expression * @param message the exception message to use if the assertion fails * @throws IllegalStateException if expression is { @code false} */ public static void state(boolean expression, String message) { if (!expression) { throw new IllegalStateException(message); } } /** * Assert a boolean expression, throwing { @link IllegalStateException} * if the test result is { @code false}. *Call {
@link #isTrue(boolean)} if you wish to * throw { @link IllegalArgumentException} on an assertion failure. *Assert.state(id == null);* @param expression a boolean expression * @throws IllegalStateException if the supplied expression is { @code false} */ public static void state(boolean expression) { state(expression, "[Assertion failed] - this state invariant must be true"); }}
方法没有几个，但是比较适用。当抛出异常IllegalStateException的时候，你可以在你的程序处理。
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