Exceptions are a common handling mechanism in Java. When an error occurs in the program, Java will throw an exception by default, and provide error details through the stack traceback information, so that developers can know when, why and where the exception occurred in the program. However, this is only part of Java's built-in exception handling. Java also provides many custom exception handling methods, allowing developers to use the exception handling mechanism more flexibly. This article discusses custom exception handling methods commonly used in Java. to sort out.
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custom exception class
In Java, you can customize exception classes to replace Java built-in exception classes. A custom exception class must inherit from the Throwable class or its subclass Exception or RuntimeException. When writing a custom exception class, you need to pay attention to the following two points:
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In general, exception classes should be defined as immutable, so they should be declared final. -
Exception classes usually need to include constructors with string parameters describing the exception that will be returned by the getMessage() method.
Here is a sample code:
public class CustomException extends Exception {
public CustomException(String message) {
super(message);
}
}
By customizing the exception class, you can convert various exceptions in the program into a specific type of exception. For example, exceptions such as IOException, FileNotFoundException, or NullPointerException may occur when reading a file, but they all indicate that the file cannot be opened or read. Then you can customize a FileReadException to replace all these exceptions.
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error code handling
Using the error coding method, we can avoid using the capture mechanism introduced in the Java exception mechanism. For some simple functions or methods, we don’t need to check the return value of the function or method every time. We only need to give different The error code can be used to judge the exception. There are three commonly used error code handling methods:
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Define an enumeration class for storing error code information. -
Define the configuration exception file, and add the error information to the property file. -
Use the system status code HTTP Status Codes to indicate the status of the request.
Here is an example of using an enumeration class:
public enum ErrorCode {
PARAM_ILLEGAL(1001, "参数非法"),
ACCOUNT_NOT_EXIST(2001, "账户不存在"),
ACCOUNT_STATUS_EXCEPTION(2002, "账户状态异常");
private final Integer code;
private final String message;
ErrorCode(Integer code, String message) {
this.code = code;
this.message = message;
}
public Integer getCode() {
return code;
}
public String getMessage() {
return message;
}
}
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Assertion handling
断言处理是通过在代码中插入一些特殊的语句，当条件成立时程序继续运行，反之则抛出一个异常。Java中提供了assert语句作为断言处理的关键字，开发人员可以在程序中使用assert（言）语句来验证某些必要的前提条件是否成立，如果不成立，则会抛出AssertionError异常。
下面是一个示例代码：
public class TestAssert {
public static void main(String[] args) {
int value = 100;
assert value > 200 : "value should be greater than 200";
}
}
在这个示例中，我们使用了assert语句来判断变量value是否大于200。如果assert条件不满足，则抛出AssertionError异常。
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应用日志处理
日志是一种非常实用的方法，可以帮助程序员对代码进行调试和问题排查，也可以用来记录有用的错误信息。在Java中，一般使用开源框架Log4j或者SLF4J等日志框架来实现日志处理机制，在程序中加入此类框架时，可以方便地记录程序的执行状态，查找并追踪程序的意外行为。同时日志记录还甚至可以定义自己的日志级别，比如DEBUG、INFO、ERROR等级别，然后根据需要定义不同的处理方式。
下面是一个应用log4j日志框架的示例代码：
public class TestLog4j {
private static final Logger logger = Logger.getLogger(TestLog4j.class);
public static void main(String[] args) {
PropertyConfigurator.configure("log4j.properties");
logger.info("info message");
logger.debug("debug message logger.error("error message");
}
}
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异常消息模板和格式化处理
异常消息模板和格式化处理可以极大地简化异常处理程序中所涉及的字符串连接和格式化问题，在Java中可以使用类似Java.util.Formatter.format() API的格式控制区域指定异常消息的模板。下面是一个示例代码：
public class Test {
public static void main(String[] args) {
String username = "user";
int age = 10;
try {
throw new CustomException(String.format("User %s,age: %s", username, age));
} catch (CustomException ex) {
System.out.println(ex.getMessage());
}
}
}
在这个示例中，我们在字符串模板中使用了String.format来构造错误消息。这样就可以避免将参数拼接成字符串，同时也可以防止SQL注入等安全问题。
总结
以上就是常见的五种Java自定义异常处理方式。对于Java开发人员来说，异常是必不可少的一个机制，了解并掌握自定义异常处理方式可以更好地利用异常处理的力量，编写出更加稳定、高效的Java程序。No matter什么情况，无论你使用哪种自定义异常处理方法都需要清晰明了地表达出异常的意义和运转背景，在实际应用过程中避免过多的繁琐处理。
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