How to handle exceptions properly in Java?
Jul 06, 2025 am 02:43 AM
The key to handling exceptions in Java is to get it right, handle it clearly, and not cover up the problem. First, we must catch specific exception types as needed, avoid general catches, and prioritize checked exceptions. Runtime exceptions should be judged in advance; second, we must use the log framework to record exceptions, and retry, rollback or throw based on the type; third, we must use the finally block to release resources, and recommend try-with-resources; fourth, we must reasonably define custom exceptions, inherit RuntimeException or Exception, and carry context information for easy debugging.
The key to handling exceptions in Java is to "acquire, handle clearly, and not cover up problems." Many people just try-catch when writing code, but really making good use of the exception mechanism can make your program more robust and easier to troubleshoot problems.
The following is based on several actual usage scenarios and talk about how to correctly handle exceptions in Java.
Identify the exception type, don't catch it in general
The exception system of Java is clearly divided, including checked exception and unchecked exception. Many newbies will write directly:
try {
// some code
} catch (Exception e) {
e.printStackTrace();
} The problem with this approach is that you don't know what's wrong, and you may also swallow some serious errors (such as OutOfMemoryError ).
? Suggestions :
- Catch specific exception types on demand, such as
IOException,SQLException, etc. - For runtime exceptions (such as
NullPointerException), try to make judgments in advance instead of relying on catch. - If you really need a guarantee, you can add a general catch at the end, but log the log and process it appropriately.
Example:
try {
// Read file} catch (FileNotFoundException e) {
logger.warn("The file does not exist, please check the path");
} catch (IOException e) {
logger.error("Error reading file", e);
}Exceptions need to be handled, not "printed"
Many people only call e.printStackTrace() after writing catch block, thinking that exception handling will be completed. In fact, this is just outputting the standard error stream, which is almost useless for online systems.
? Suggestions :
- Use log frameworks (such as Log4j, SLF4J) to record exception information to facilitate subsequent troubleshooting.
- Decide whether to retry, rollback or notify the upper layer based on the exception type.
- If it is currently unavailable, it should be thrown or encapsulated and thrown, allowing the caller to handle it.
Example:
try {
// Database operation} catch (SQLException e) {
logger.error("Database operation failed", e);
throw new MyCustomException("DB error occurred", e);
}Don't ignore the role of finally
The finally block is used to perform cleanup work, such as closing resources, releasing locks, etc. Even if there is a return or an exception is thrown in try or catch, the code in finally executes.
? Suggestions :
- All resources that need to be released (such as IO streams, database connections) should be placed in finally blocks.
- Java 7 supports try-with-resources writing, and it is recommended to use it first.
Example:
try (FileInputStream fis = new FileInputStream("file.txt")) {
// Read content} catch (IOException e) {
// Handle exception}
// fis is automatically closed, and does not need to be manually handled in finallyUse custom exceptions reasonably
Sometimes the exception types provided by JDK are not enough to express the business meaning, so you need to customize the exception.
? Suggestions :
- Custom exceptions should inherit
RuntimeExceptionorExceptionand decide whether to force processing. - The exception name should be meaningful to facilitate the positioning of problems.
- You can carry additional information (such as error codes, context data) to help debug.
Example:
public class UserNotFoundException extends RuntimeException {
public UserNotFoundException(String message) {
super(message);
}
}Exception handling is not a simple "try-catch", but a guarantee of the robustness of the program. After mastering these basic techniques, you will find that the code is not only clearer, but also easier to locate when something goes wrong.
Basically all this is not complicated but easy to ignore.
The above is the detailed content of How to handle exceptions properly in Java?. For more information, please follow other related articles on the PHP Chinese website!
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