建立業務 Exception

一般在實際專案中，推薦建立自己的 Exception 型別，這樣在後期會更容易處理，也比較方便統一，否則，可能每個人都丟擲自己喜歡的異常型別，而造成程式碼混亂

ServiceException 用於丟擲業務邏輯校驗異常

UnauthorizedException 用於丟擲使用者未登入異常

可根據自己的專案需求變化，但簡單專案中這兩個已經夠用

ServiceException

package cn.myesn.exception;

public class ServiceException extends RuntimeException {

    /**
     * Constructs a new runtime exception with {@code null} as its
     * detail message.  The cause is not initialized, and may subsequently be
     * initialized by a call to {@link #initCause}.
     */
    public ServiceException() {
        super();
    }

    /**
     * Constructs a new runtime exception with the specified detail message.
     * The cause is not initialized, and may subsequently be initialized by a
     * call to {@link #initCause}.
     *
     * @param message the detail message. The detail message is saved for
     *                later retrieval by the {@link #getMessage()} method.
     */
    public ServiceException(String message) {
        super(message);
    }

    /**
     * Constructs a new runtime exception with the specified detail message and
     * cause.  <p>Note that the detail message associated with
     * {@code cause} is <i>not</i> automatically incorporated in
     * this runtime exception's detail message.
     *
     * @param message the detail message (which is saved for later retrieval
     *                by the {@link #getMessage()} method).
     * @param cause   the cause (which is saved for later retrieval by the
     *                {@link #getCause()} method).  (A <tt>null</tt> value is
     *                permitted, and indicates that the cause is nonexistent or
     *                unknown.)
     * @since 1.4
     */
    public ServiceException(String message, Throwable cause) {
        super(message, cause);
    }

    /**
     * Constructs a new runtime exception with the specified cause and a
     * detail message of <tt>(cause==null ? null : cause.toString())</tt>
     * (which typically contains the class and detail message of
     * <tt>cause</tt>).  This constructor is useful for runtime exceptions
     * that are little more than wrappers for other throwables.
     *
     * @param cause the cause (which is saved for later retrieval by the
     *              {@link #getCause()} method).  (A <tt>null</tt> value is
     *              permitted, and indicates that the cause is nonexistent or
     *              unknown.)
     * @since 1.4
     */
    public ServiceException(Throwable cause) {
        super(cause);
    }

    /**
     * Constructs a new runtime exception with the specified detail
     * message, cause, suppression enabled or disabled, and writable
     * stack trace enabled or disabled.
     *
     * @param message            the detail message.
     * @param cause              the cause.  (A {@code null} value is permitted,
     *                           and indicates that the cause is nonexistent or unknown.)
     * @param enableSuppression  whether or not suppression is enabled
     *                           or disabled
     * @param writableStackTrace whether or not the stack trace should
     *                           be writable
     * @since 1.7
     */
    protected ServiceException(String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace) {
        super(message, cause, enableSuppression, writableStackTrace);
    }
}
 

UnauthorizedException

package cn.myesn.exception;

public class UnauthorizedException extends RuntimeException {
    /**
     * Constructs a new runtime exception with {@code null} as its
     * detail message.  The cause is not initialized, and may subsequently be
     * initialized by a call to {@link #initCause}.
     */
    public UnauthorizedException() {
        super();
    }

    /**
     * Constructs a new runtime exception with the specified detail message.
     * The cause is not initialized, and may subsequently be initialized by a
     * call to {@link #initCause}.
     *
     * @param message the detail message. The detail message is saved for
     *                later retrieval by the {@link #getMessage()} method.
     */
    public UnauthorizedException(String message) {
        super(message);
    }

    /**
     * Constructs a new runtime exception with the specified detail message and
     * cause.  <p>Note that the detail message associated with
     * {@code cause} is <i>not</i> automatically incorporated in
     * this runtime exception's detail message.
     *
     * @param message the detail message (which is saved for later retrieval
     *                by the {@link #getMessage()} method).
     * @param cause   the cause (which is saved for later retrieval by the
     *                {@link #getCause()} method).  (A <tt>null</tt> value is
     *                permitted, and indicates that the cause is nonexistent or
     *                unknown.)
     * @since 1.4
     */
    public UnauthorizedException(String message, Throwable cause) {
        super(message, cause);
    }

    /**
     * Constructs a new runtime exception with the specified cause and a
     * detail message of <tt>(cause==null ? null : cause.toString())</tt>
     * (which typically contains the class and detail message of
     * <tt>cause</tt>).  This constructor is useful for runtime exceptions
     * that are little more than wrappers for other throwables.
     *
     * @param cause the cause (which is saved for later retrieval by the
     *              {@link #getCause()} method).  (A <tt>null</tt> value is
     *              permitted, and indicates that the cause is nonexistent or
     *              unknown.)
     * @since 1.4
     */
    public UnauthorizedException(Throwable cause) {
        super(cause);
    }

    /**
     * Constructs a new runtime exception with the specified detail
     * message, cause, suppression enabled or disabled, and writable
     * stack trace enabled or disabled.
     *
     * @param message            the detail message.
     * @param cause              the cause.  (A {@code null} value is permitted,
     *                           and indicates that the cause is nonexistent or unknown.)
     * @param enableSuppression  whether or not suppression is enabled
     *                           or disabled
     * @param writableStackTrace whether or not the stack trace should
     *                           be writable
     * @since 1.7
     */
    protected UnauthorizedException(String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace) {
        super(message, cause, enableSuppression, writableStackTrace);
    }
}
 

建立異常返回值包裝類

package cn.myesn.exception;

import lombok.Data;
import lombok.experimental.Accessors;

@Data
@Accessors(chain = true)
public class GlobalExceptionResponseResult {
    private String message;
}

建立全域性異常處理者

建立 GlobalExceptionHandler 處理類，該類處理 spring boot rest controller 中丟擲的所有異常

package cn.myesn.handler;

import cn.myesn.exception.GlobalExceptionResponseResult;
import cn.myesn.exception.ServiceException;
import cn.myesn.exception.UnauthorizedException;
import org.springframework.http.HttpStatus;
import org.springframework.http.converter.HttpMessageNotReadableException;
import org.springframework.validation.BindException;
import org.springframework.validation.ObjectError;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.web.bind.annotation.RestControllerAdvice;

@RestControllerAdvice
public class GlobalExceptionHandler {

    // 根本就沒有傳遞引數時的異常
    @ExceptionHandler(HttpMessageNotReadableException.class)
    @ResponseStatus(value = HttpStatus.BAD_REQUEST)
    public GlobalExceptionResponseResult handle(HttpMessageNotReadableException e) {
        return new GlobalExceptionResponseResult().setMessage("引數不能為空");
    }

    // 傳了引數，但沒有通過 validation 時的異常
    @ExceptionHandler(BindException.class)
    @ResponseStatus(value = HttpStatus.BAD_REQUEST)
    public GlobalExceptionResponseResult handle(BindException e) {
        final ObjectError objectError = e.getBindingResult().getAllErrors().get(0);
        return new GlobalExceptionResponseResult().setMessage(objectError.getDefaultMessage());
    }

    // 程式碼中丟擲的邏輯異常
    @ExceptionHandler(ServiceException.class)
    @ResponseStatus(value = HttpStatus.BAD_REQUEST)
    public GlobalExceptionResponseResult handle(ServiceException e) {
        return new GlobalExceptionResponseResult().setMessage(e.getMessage());
    }

    // 未登入異常
    @ExceptionHandler(UnauthorizedException.class)
    @ResponseStatus(value = HttpStatus.UNAUTHORIZED)
    public void handle(UnauthorizedException e) {
    }

    // 但以上幾種錯誤都未能匹配到時，catch 一個基礎的異常型別，基本上能捕獲所有該捕獲的異常型別
    @ExceptionHandler(RuntimeException.class)
    @ResponseStatus(value = HttpStatus.BAD_REQUEST)
    public GlobalExceptionResponseResult handle(RuntimeException e) {
        return new GlobalExceptionResponseResult().setMessage(String.format("未處理的異常：%s", e.getMessage()));
    }
}
 

實際使用

新建一個 TestController 檔案，在裡面新增如下端點：

@GetMapping("check-username")
public ResponseEntity<?> checkUsername(@RequestParam String username) {
    if (StringUtils.isBlank(username)) {
        throw new ServiceException("使用者名稱不能為空");
    }

    if (userService.existsUserName(username)) {
        throw new ServiceException("使用者名稱已存在");
    }

    return ResponseEntity.ok().build();
}

這樣，寫業務程式碼時，throw 就行了，程式碼整體更符合語義，也更加簡潔明瞭