Java中Spring的Assert断言的使用
Java中Assert的使用日常较少, 使用Assert可以提高代码的可读性,但过度使用,会导致不利于后期代码的维护.
1 Spring的Assert的简介
Java中断言assert是一个关键字, 主要是验证某些条件是否成立. 在一些编辑器中,需要开启assert断言功能,才可以使用,如IDEA,Eclipse等 ,很不方便使用,在生产等环境不适用, 故常常使用的是Spring框架封装的org.springframework.util.Assert断言.
部分源代码:
public abstract class Assert { /** * Assert a boolean expression, throwing an {@code IllegalStateException} * if the expression evaluates to {@code false}. * <p>Call {@link #isTrue} if you wish to throw an {@code 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 {@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 IllegalStateException} * if the expression evaluates to {@code false}. * <p>Call {@link #isTrue} if you wish to throw an {@code IllegalArgumentException} * on an assertion failure. * <pre> * Assert.state(entity.getId() == null, * () -> "ID for entity " + entity.getName() + " must not already be initialized"); * </pre> * @param expression a boolean expression * @param messageSupplier a supplier for the exception message to use if the * assertion fails * @throws IllegalStateException if {@code expression} is {@code false} * @since 5.0 */ public static void state(boolean expression, Supplier<String> messageSupplier) { if (!expression) { throw new IllegalStateException(nullSafeGet(messageSupplier)); } } /** * Assert a boolean expression, throwing an {@code IllegalStateException} * if the expression evaluates to {@code false}. * @deprecated as of 4.3.7, in favor of {@link #state(boolean, String)} */ @Deprecated public static void state(boolean expression) { state(expression, "[Assertion failed] - this state invariant must be true"); } /** * Assert a boolean expression, throwing an {@code IllegalArgumentException} * if the expression evaluates to {@code false}. * <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 {@code expression} is {@code false} */ public static void isTrue(boolean expression, String message) { if (!expression) { throw new IllegalArgumentException(message); } } /** * Assert a boolean expression, throwing an {@code IllegalArgumentException} * if the expression evaluates to {@code false}. * <pre> * Assert.isTrue(i > 0, () -> "The value '" + i + "' must be greater than zero"); * </pre> * @param expression a boolean expression * @param messageSupplier a supplier for the exception message to use if the * assertion fails * @throws IllegalArgumentException if {@code expression} is {@code false} * @since 5.0 */ public static void isTrue(boolean expression, Supplier<String> messageSupplier) { if (!expression) { throw new IllegalArgumentException(nullSafeGet(messageSupplier)); } } /** * Assert a boolean expression, throwing an {@code IllegalArgumentException} * if the expression evaluates to {@code false}. * @deprecated as of 4.3.7, in favor of {@link #isTrue(boolean, String)} */ @Deprecated public static void isTrue(boolean expression) { isTrue(expression, "[Assertion failed] - this expression must be true"); } } 复制代码从代码可知,Assert断言的表达式基本分为两类
Assert.方法名 (布尔表达式) : 这类方法都标记过时, 都调用第二类方法
Assert.方法名 (布尔表达式,错误提示信息) : 这类方法, 如果布尔表达式不满足,会抛出异常,并将异常信息封装.
在使用方法时不满足布尔表达式, 就会抛出相应的异常,如IllegalStateException和IllegalArgumentException, 此类异常都属于运行时异常.
2 Spring的Assert的使用
if (条件为真) { // 业务处理 } 复制代码上述可替换成
Assert.isTrue(条件为真, "条件不满足"); // 业务处理 复制代码
public static void main(String[] args) { Assert.isTrue(1>0); System.out.println("断言 1>0 成功"); Assert.isTrue(1 < 0, "断言1 < 0失败"); } /* 运行结果: Exception in thread "main" 断言 1>0 成功 java.lang.IllegalArgumentException: 断言1 < 0失败 at org.springframework.util.Assert.isTrue(Assert.java:121) at com.cf.demo.config.MailTest2.main(MailTest2.java:61) */ 复制代码使用时发现,Spring中主要抛出非法参数异常和非法状态异常, 主要用来做参数的校验,可以提高代码的可读性.对于一些说法, 关于可以替代if-else语句, 是不合理的. if-else主要用来做条件分支判断,满足那个就进入那个, 而Assert断言,满足条件才会向下运行,不满足,直接抛出异常,二者应用场景不一致.
作者：ABestRookie
链接：https://juejin.cn/post/7026357154374221855