【JAVA基础】错误捕获try-catch

错误捕获try-catch

使用BaseController统一管理

项目结构



UserController

package com.cy.store.controller;

import com.cy.store.entity.User;
import com.cy.store.service.IUserService;
import com.cy.store.service.ex.InsertException;
import com.cy.store.service.ex.UsernameDuplicatedException;
import com.cy.store.util.JsonResult;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController //其作用等同于@Controller+@ResponseBody
//@Controller
@RequestMapping("users")
public class UserController extends BaseController {

    @Autowired
    private IUserService userService;

    @RequestMapping("/reg")
    //@ResponseBody //表示此方法的响应结果以json格式进行数据的响应给到前端
    public JsonResult<Void> reg(User user) {
        userService.reg(user);
        return new JsonResult<>(OK);
    }

    /*public JsonResult<Void> reg(User user) {
        //创建响应结果对象即JsonResult对象
        JsonResult<Void> result = new JsonResult<>();
        try {
            //调用userService的reg方法时可能出现异常,所以需要捕获异常
            userService.reg(user);
            result.setState(200);
            result.setMessage("用户注册成功");
        } catch (UsernameDuplicatedException e) {
            result.setState(4000);
            result.setMessage("用户名被占用");
        } catch (InsertException e) {
            result.setState(5000);
            result.setMessage("注册时产生未知的异常");
        }
        return result;
    }*/
}

BaseController

package com.cy.store.controller;

import com.cy.store.service.ex.InsertException;
import com.cy.store.service.ex.ServiceException;
import com.cy.store.service.ex.UsernameDuplicatedException;
import com.cy.store.util.JsonResult;
import org.springframework.web.bind.annotation.ExceptionHandler;

public class BaseController {

    //操作成功的状态码
    public static final int OK = 200;

    /**
     * 1.@ExceptionHandler表示该方法用于处理捕获抛出的异常
     * 2.什么样的异常才会被这个方法处理呢?所以需要ServiceException.class,这样的话只要是抛出ServiceException异常就会被拦截到handleException方法,此时handleException方法就是请求处理方法,返回值就是需要传递给前端的数据
     * 3.被ExceptionHandler修饰后如果项目发生异常,那么异常对象就会被自动传递给此方法的参数列表上,所以形参就需要写Throwable e用来接收异常对象
     */
    @ExceptionHandler(ServiceException.class)
    public JsonResult<Void> handleException(Throwable e) {
        JsonResult<Void> result = new JsonResult<>(e);
        if (e instanceof UsernameDuplicatedException) {
            result.setState(4000);
            result.setMessage("用户名已经被占用");
        } else if (e instanceof InsertException) {
            result.setState(5000);
            result.setMessage("插入数据时产生未知的异常");
        }
        return result;
    }
}

ServiceException

package com.cy.store.service.ex;

/**
 * 因为整个业务的异常只有一种情况下才会产生:只有运行时才会产生,不运行不会产生
 * 所以要求业务层的异常都要继承运行时异常RuntimeException并且重写父类的所有构造方法以便后期能抛出自已定义的异常
 * 例:throws new ServiceException("业务层产生未知异常")
 */
public class ServiceException extends RuntimeException {
    public ServiceException() {
        super();
    }

    public ServiceException(String message) {
        super(message);
    }

    public ServiceException(String message, Throwable cause) {
        super(message, cause);
    }

    public ServiceException(Throwable cause) {
        super(cause);
    }

    protected ServiceException(String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace) {
        super(message, cause, enableSuppression, writableStackTrace);
    }
}

InsertException

package com.cy.store.service.ex;

//数据插入过程中产生异常
public class InsertException extends ServiceException{
    /**重写ServiceException的所有构造方法*/
    public InsertException() {
        super();
    }

    public InsertException(String message) {
        super(message);
    }

    public InsertException(String message, Throwable cause) {
        super(message, cause);
    }

    public InsertException(Throwable cause) {
        super(cause);
    }

    protected InsertException(String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace) {
        super(message, cause, enableSuppression, writableStackTrace);
    }
}

UsernameDuplicatedException

package com.cy.store.service.ex;

public class UsernameDuplicatedException extends ServiceException{
    /**重写ServiceException的所有构造方法*/
    public UsernameDuplicatedException() {
        super();
    }

    public UsernameDuplicatedException(String message) {
        super(message);
    }

    public UsernameDuplicatedException(String message, Throwable cause) {
        super(message, cause);
    }

    public UsernameDuplicatedException(Throwable cause) {
        super(cause);
    }

    protected UsernameDuplicatedException(String message, Throwable cause, boolean enableSuppression, boolean writableStackTrace) {
        super(message, cause, enableSuppression, writableStackTrace);
    }
}