获取名为 DAO 类的 Bean 创建异常

Question

当我构建此代码时，即使正确添加了注释，我也会收到错误 bean 没有为 DAO 类创建

警告：上下文初始化期间遇到异常 - 取消刷新尝试： org.springframework.beans.factory.BeanCreationException： 创建名为"bankDaoImpl"的 bean 时出错 在文件 [C：\Users\saivi\eclipse- workspace\bank\target\classes\com\bank\dao\BankDaoImpl.class]：Bean 的实例化失败;嵌 套 异常是 org.springframework.beans.BeanInstantiationException： 无法实例化 [com.bank.dao.bankDaoImpl]：构造函数抛出异常;嵌套异常是 java.lang.NullPointerException 2019-11-28下午09：50：45 org.springframework.web.context.ContextLoader initWebApplicationContext SEVERE：上下文初始化失败 org.springframework.beans.factory.BeanCreationException： 创建名为"bankDaoImpl"的 bean 时出错 在文件 [C：\Users\saivi\eclipse- workspace\bank\target\classes\com\bank\dao\BankDaoImpl.class]：Bean 的实例化失败;嵌 套 异常是 org.springframework.beans.BeanInstantiationException： 无法实例化 [com.bank.dao.bankDaoImpl]：构造函数抛出异常;嵌套异常是 java.lang.NullPointerException

应用配置.java

包 com.bank.config;

import java.util.Properties;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.ComponentScans;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.core.env.Environment;
import org.springframework.orm.hibernate5.HibernateTransactionManager;
import org.springframework.orm.hibernate5.LocalSessionFactoryBean;
import org.springframework.transaction.annotation.EnableTransactionManagement;
import static org.hibernate.cfg.Environment.*;
@Configuration
@PropertySource("classpath:db.properties")
@EnableTransactionManagement
@ComponentScans(value = { @ComponentScan("com.bank.dao"),
@ComponentScan("com.bank.service") })
public class AppConfig {
@Autowired
private Environment env;
@Bean
public LocalSessionFactoryBean getSessionFactory() {
LocalSessionFactoryBean factoryBean = new LocalSessionFactoryBean();
Properties props = new Properties();
// Setting JDBC properties
props.put(DRIVER, env.getProperty("mysql.driver"));
props.put(URL, env.getProperty("mysql.url"));
props.put(USER, env.getProperty("mysql.user"));
props.put(PASS, env.getProperty("mysql.password"));
// Setting Hibernate properties
props.put(SHOW_SQL, env.getProperty("hibernate.show_sql"));
props.put(HBM2DDL_AUTO, env.getProperty("hibernate.hbm2ddl.auto"));
// Setting C3P0 properties
props.put(C3P0_MIN_SIZE, env.getProperty("hibernate.c3p0.min_size"));
props.put(C3P0_MAX_SIZE, env.getProperty("hibernate.c3p0.max_size"));
props.put(C3P0_ACQUIRE_INCREMENT, 
env.getProperty("hibernate.c3p0.acquire_increment"));
props.put(C3P0_TIMEOUT, env.getProperty("hibernate.c3p0.timeout"));
props.put(C3P0_MAX_STATEMENTS, env.getProperty("hibernate.c3p0.max_statements"));
factoryBean.setHibernateProperties(props);
factoryBean.setPackagesToScan("com.bank.model");
return factoryBean;
}
@Bean
public HibernateTransactionManager getTransactionManager() {
HibernateTransactionManager transactionManager = new HibernateTransactionManager();
transactionManager.setSessionFactory(getSessionFactory().getObject());
return transactionManager;
}
}

MyWebApp初始值设定项.java

package com.bank.config;
import org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer;
public class MyWebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
@Override
protected Class<?>[] getRootConfigClasses() {
return new Class[] {AppConfig.class};
}
@Override
protected Class<?>[] getServletConfigClasses() {
return new Class[] {WebConfig.class};
}
@Override
protected String[] getServletMappings() {
return new String[] {"/"};
}
}

网络配置.java

package com.bank.config;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;
@Configuration
@EnableWebMvc
@ComponentScan(basePackages= {"com.bank.controller"})
public class WebConfig extends WebMvcConfigurerAdapter {
}

银行.java

package com.bank.model;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
@Entity(name="Bank")
public class Bank {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private long id;
private String name;
private Integer balance;
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getBalance() {
return balance;
}
public void setBalance(Integer balance) {
this.balance = balance;
}
}

银行道.java

package com.bank.dao;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Repository;
import com.bank.model.Bank;
@Repository
public class BankDaoImpl implements BankDao{
@Autowired
private SessionFactory sessionFactory;
Session s=sessionFactory.getCurrentSession();

@Override
public long save(Bank bank) {
s.save(bank);
return bank.getId();
}
@Override
public Bank get(long id) {
return s.get(Bank.class, id);
}

@Override
public void delete(long id) {
Bank b=s.byId(Bank.class).load(id);
s.delete(b);
}
}

银行服务.java

package com.bank.service;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import com.bank.dao.BankDao;
import com.bank.model.Bank;
@Service
@Transactional(readOnly=true)
public class BankServiceImpl implements BankService {
@Autowired
private BankDao bankDao;
@Transactional
@Override
public long save(Bank bank) {
return bankDao.save(bank);
}
@Override
public Bank get(long id) {
return bankDao.get(id);
}
@Override
public void delete(long id) {
bankDao.delete(id);
}
}

绒球.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>bank</groupId>
<artifactId>bank</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>war</packaging>
<properties>
<failOnMissingWebXml>false</failOnMissingWebXml>
</properties>
<dependencies>
<!-- Spring MVC Dependency -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-webmvc</artifactId>
<version>4.3.10.RELEASE</version>
</dependency>
<!-- Spring ORM -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-orm</artifactId>
<version>4.3.10.RELEASE</version>
</dependency>
<!-- Hibernate ORM -->
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>5.2.11.Final</version>
</dependency>
<!-- Hibernate-C3P0 Integration -->
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-c3p0</artifactId>
<version>5.2.11.Final</version>
</dependency>
<!-- c3p0 -->
<dependency>
<groupId>com.mchange</groupId>
<artifactId>c3p0</artifactId>
<version>0.9.5.2</version>
</dependency>
<!-- Mysql Connector -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>6.0.5</version>
</dependency>
<!-- Jackson API for JSON -->
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.8.7</version>
</dependency>
<!-- Servlet Dependency -->
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>3.1.0</version>
<scope>provided</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.5.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
<!-- Embedded Apache Tomcat required for testing web application -->
<plugin>
<groupId>org.apache.tomcat.maven</groupId>
<artifactId>tomcat7-maven-plugin</artifactId>
<version>2.2</version>
<configuration>
<path>/</path>
</configuration>
</plugin>
</plugins>
</build>
</project>

Answer 1

代码示例中的以下行Session s=sessionFactory.getCurrentSession();BankDaoImpl将导致NullPointerException，因为SessionFactory对象尚未自动连线，并且您已经在尝试调用其方法。

尝试将该行替换到该类中的每个方法中。例如，您的BankDaoImpl#save方法将如下所示：

public class BankDaoImpl {
@Autowired
SessionFactory sessionFactory;
@Override
public long save(Bank bank) {
Session s = sessionFactory.getCurrentSession();
s.save(bank);
return bank.getId();
}
...
}

尝试对在BankDaoImpl类中使用sessionFactory的所有其他方法执行上述操作。