Best practice record of throws keyword handling exceptions in Java

In Java programming, exception handling is an important means to ensure the robustness and stability of the program. In addition to usingtry-catchIn addition to block catching exceptions, Java also providesthrowsKeywords allow us to throw exceptions to the caller for processing. Today, we will discuss in depththrowsKeyword usage, applicable scenarios, and best practices help you write more elegant and easier to maintain code.

1. Basic usage of throws keyword

throwsKeywords are used in method signatures and declare the type of exception that the method may throw. When some kind of exception may be thrown inside the method but do not want to be processed in the current method, you can usethrowsThrow the exception to the caller for processing.

grammar:

Return type Method name(Parameter list) throws Exception type1, Exception type2, ... {
    // Method body}

Example:

public void readFile(String filePath) throws IOException {
    FileReader fileReader = new FileReader(filePath);
    // Other operations}

In this example,readFileMethods may be thrownIOException, but it is not processed inside the method, but throughthrowsDeclares throws exceptions to the caller.

2. The difference between throws and try-catch

try-catch: Catch and handle exceptions inside the method, suitable for handling known and recoverable exceptions.
throws: Throw the exception to the caller for processing, suitable for handling exceptions that cannot be handled in the current method, or hope that the caller will decide how to handle the exception.

Use scenario comparison:

If you can handle exceptions inside the method (such as logging, retrying operations, etc.), usetry-catch。
If you think that the exception should be handled by the caller (for example, the caller needs to decide on subsequent logic based on the exception type), usethrows。

3. Applicable scenarios for throws

When the method cannot handle the exception
When the method cannot handle some exception internally, it can be usedthrowsThrows the exception to the caller. For example, a file read method may throwIOException, but the specific processing logic (such as retry, prompting the user, etc.) should be decided by the caller.

Exception pass in hierarchical architecture
In a hierarchical architecture (such as Controller-Service-DAO), exceptions are usually thrown at the DAO layer and then handled uniformly in the Service layer or Controller layer. passthrowsKeywords, can pass exceptions from the bottom to the upper layer.

Custom exception throwing
When the method needs to throw a custom exception, it can be usedthrowsstatement. For example:

public void validateUser(User user) throws InvalidUserException {
    if (user == null || () == null) {
        throw new InvalidUserException("User information is invalid");
    }
}

4. Precautions for using throws

Identify the exception type
Use in method signaturethrowsWhen you are not sure about the exception types that may be thrown, you should clearly declare them to avoid using too broad exception types (such asthrows Exception), which will make it difficult for the caller to handle.

Avoid overuse of throws
If every place in the method that may throw an exception is usedthrows, will cause the caller code to become complicated. It is recommended to use it in appropriate placestry-catchHandle exceptions instead of throwing all exceptions to the caller.

Relationship with inheritance
When a subclass overrides the parent class method,throwsThe declared exception type cannot be broader than the exception type declared by the parent class method. For example:

class Parent {
    void method() throws IOException {}
}
class Child extends Parent {
    // Correct: Subclasses can not throw exceptions, or throw more specific exceptions    @Override
    void method() throws FileNotFoundException {}
}

Differences from RuntimeException
RuntimeExceptionand its subclasses (e.g.NullPointerException、IllegalArgumentException) is an exception that is not checked and does not need to be used in the method signaturethrowsstatement. Check for abnormalities (such asIOException、SQLException) Must be explicitly declared or captured.

5. Best practices for throws

Layered exception handling
In a hierarchical architecture, it is recommended to throw exceptions at the bottom layer (such as the DAO layer) and handle them uniformly at the top layer (such as the Service layer or the Controller layer). This avoids duplicate code for exception handling.

Encapsulate exception information
When an exception is thrown, try to provide meaningful exception information to facilitate the caller to understand and handle it. For example:

throw new IOException("File reading failed, path:" + filePath);

Combined with custom exceptions
For specific errors in business logic, custom exceptions can be defined and passedthrowsThrow out. For example:

public void withdraw(double amount) throws InsufficientBalanceException {
    if (amount &gt; balance) {
        throw new InsufficientBalanceException("Insufficient balance");
    }
    // Other logic}

Avoid abuse of throws
Don't throw all exceptions to the caller, especially those that can be handled in the current method. OverusethrowsWill increase the burden on the caller.

6. Sample code

Here is a complete example showingthrowsKeyword usage scenarios:

import ;
import ;
public class FileUtil {
    // Method declaration may throw IOException    public static String readFileContent(String filePath) throws IOException {
        FileReader fileReader = new FileReader(filePath);
        StringBuilder content = new StringBuilder();
        int ch;
        while ((ch = ()) != -1) {
            ((char) ch);
        }
        ();
        return ();
    }
    public static void main(String[] args) {
        try {
            String content = readFileContent("");
            ("File Content:" + content);
        } catch (IOException e) {
            ("File reading failed:" + ());
        }
    }
}

In this example,readFileContentMethod declares possible throwIOException,andmainThe method is responsible for catching and handling the exception.

7. Summary

throwsKeywords are an important part of Java exception handling mechanism. They allow us to throw exceptions to the caller for processing, suitable for scenarios where exceptions cannot be handled in the current method. By reasonable usethrows, we can make the code more modular and easy to maintain. However, overusethrowsIt also increases the burden on the caller, so it needs to be weighed according to the actual situation.

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