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/*
 * Copyright 2002-2017 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 com.feilong.lib.springframework.util;

/**
 * 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 Sam Brannen
 * @author Colin Sampaleanu
 * @author Rob Harrop
 * @since 1.1.2
 */
public abstract class Assert{

    /**
     * Assert a boolean expression, throwing an {@code IllegalStateException}
     * if the expression evaluates to {@code false}.
     * 

     * Call {@link #isTrue} if you wish to throw an {@code 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 {@code expression} is {@code false}
     */
    public static void state(boolean expression,String message){
        if (!expression){
            throw new IllegalStateException(message);
        }
    }

    /**
     * Assert a boolean expression, throwing an {@code IllegalArgumentException}
     * if the expression evaluates to {@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 {@code expression} is {@code false}
     */
    public static void isTrue(boolean expression,String message){
        if (!expression){
            throw new IllegalArgumentException(message);
        }
    }

    /**
     * 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);
        }
    }

}