Spring mvc 我在我的SpringMVC项目中得到了NullPointerException？

我有一个基于SpringMVC框架的简单库项目。我将向我的author表中添加一个新的author，但是我得到了NullPointerException。 我在下面提供了与此函数相关的添加类。有人能说什么不对吗

@Controller
public class AuthorController {

@RequestMapping("/addAuthor")
protected ModelAndView addAuthor() throws Exception {
    ModelAndView model = new ModelAndView("addAuthor");
    return model;
}

@RequestMapping("/addAuthorExecution")
protected ModelAndView addAuthorExecution(
        @RequestParam("authorName") String authorName) throws Exception {
    ApplicationContext cnx = new ClassPathXmlApplicationContext("spring.xml");
    AuthorService authorService = (AuthorService) cnx.getBean("authorService");
    authorService.addAuthor(authorName);
    ModelAndView model = new ModelAndView("adminFunctionsPage");
    model.addObject("successMsg", "Your request has been processed Successfully.");
    return model;
}
}

服务类别：

public class AuthorService {
@Autowired
Author author;
@Autowired
AuthorDAO authorDAO;

public void addAuthor(String authorName) throws ClassNotFoundException,
        SQLException {
    AuthorDAO authorDAO = new AuthorDAO();
    authorDAO.addAuthor(authorName);
}
}

DAO类：

public class AuthorDAO extends JdbcDaoSupport {

public void addAuthor(String authorName) {
    String sql = "insert into tbl_author (authorName) values (?)";
    this.getJdbcTemplate().update(sql, new Object[] { authorName });
}


private static final class AuthorMapper implements RowMapper<Author> {
    @Autowired
    Author author;

    @Override
    public Author mapRow(ResultSet rs, int rowNum) throws SQLException {
        author.setAuthorId(rs.getInt("authorId"));
        author.setAuthorName(rs.getString("authorName"));
        return author;
    }

}
}

XML:

---

你好，你能试试吗

<property name="url" value="jdbc:mysql://localhost:3306/library"/>

而不是

<property name="url" value="jdbc:mysql://localhost/library"/>

这将是一个问题

几个错误

您正在自动连接POJO实体类

Auther

。这是错误的

希望您在

AuthorService

您正在

addAuthor

方法内创建

AuthorDAO

的对象。您应该注意，不应手动构造

AutherDAO

，因为该类

AutherDAO.AuthorMapper

中有

autowired

对象可用。通过手动构造它们，这些自动连接将不会连接到对象

如果我完全重写您的服务类，它将是这样的

    @Service
    public class AuthorService {

        @Autowired
        AuthorDAO authorDAO;

        public void addAuthor(String authorName) throws Exception {
           authorDAO.addAuthor(authorName);
        }
    }

---

错误出现在AuthorDAO的第32行。这条线是什么？你推断出什么？你不认为行映射程序应该为每一行创建一个新的作者，而不是每次调用它时都修改同一个（不是）自动连接的作者吗？另一方面，既然已经有了AuthorDAO，为什么还要构造一个AuthorDAO呢？它是由Spring在服务中自动连接的。问题是我的服务类中的附加AuthorDAO。谢谢你的评论。

<property name="url" value="jdbc:mysql://localhost:3306/library"/>

<property name="url" value="jdbc:mysql://localhost/library"/>

    @Service
    public class AuthorService {

        @Autowired
        AuthorDAO authorDAO;

        public void addAuthor(String authorName) throws Exception {
           authorDAO.addAuthor(authorName);
        }
    }