java - Java Spring @Autowired无法按预期工作

Question

由于@Autowired，我的应用程序未按预期运行。
是否因为下面的代码？

@PropertySource("WEB-INF/config.properties")
public class DBQuery {
    @Autowired
    private Environment env;

我尝试了2天的大量可用解决方案和示例，但没有希望让我的应用程序正常运行。非常感谢那些可以使用我的代码纠正我的人。

错误消息

2016-12-15 14:23:04 WARN  XmlWebApplicationContext:487 - Exception encountered during context initialization - cancelling refresh attempt
org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'dbQuery' defined in ServletContext resource [/WEB-INF/test-servlet.xml]: Unsatisfied dependency expressed through constructor argument with index 0 of type [java.lang.String]: : No qualifying bean of type [java.lang.String] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {}; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [java.lang.String] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {}
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [java.lang.String] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {}

尝试以下下面的解决方案后更新了完整堆栈错误消息

<bean id="dbQuery" class="com.cdmDP.db.DBQuery" >
    <constructor-arg type="java.lang.String" value="1"/>
</bean>

2016-12-15 15:46:49 ERROR ContextLoader:331 - Context initialization failed
org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'DBQuery' defined in file [D:\program_files\apache-tomcat-8.0.39\webapps\test\WEB-INF\classes\com\test\db\DBQuery.class]: Unsatisfied dependency expressed through constructor argument with index 0 of type [java.lang.String]: : No qualifying bean of type [java.lang.String] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {}; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [java.lang.String] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {}
        at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:749)
        at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:185)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1139)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1042)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:504)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
        at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303)
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299)
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:755)
        at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:757)
        at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:480)
        at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:403)
        at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:306)
        at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:106)
        at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4853)
        at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5314)
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
        at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:753)
        at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:729)
        at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:717)
        at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:940)
        at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1816)
        at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
        at java.util.concurrent.FutureTask.run(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [java.lang.String] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {}
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:1301)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1047)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:942)
        at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:813)
        at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:741)
        ... 28 more

com / test / ViewAllData.java

@Controller
public class ViewAllData {
    DBQuery dbQuery;

    @Autowired
    public ViewAllData(DBQuery dbQuery){
        this.dbQuery = dbQuery;
    }

    @RequestMapping("/viewAllData")
    public ModelAndView viewData() throws SQLException, ClassNotFoundException{
        String dataTable;
        ResultSet rs = dbQuery.getAllData();
        //processing

        return new ModelAndView("viewAllData", "message", dataTable);
    }
}

com / test / db / DBQuery.java

@Controller
@Service
@PropertySource("WEB-INF/config.properties")
public class DBQuery {
    @Autowired
    private Environment env;
    String dbUsername = env.getProperty("db.username");
    String dbPassword = env.getProperty("db.password");
    String dbUrl = env.getProperty("db.url");

    String start;
    @Autowired
    public DBQuery(String start) throws ClassNotFoundException, SQLException{
        this.start = start;
    }

    public ResultSet getAllDataPassport() throws SQLException, ClassNotFoundException{
        Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");  
        Connection conn = DriverManager.getConnection(dbUrl, dbUsername, dbPassword);

        Statement statement = conn.createStatement();
        String sql = "select * from testing_table";
        ResultSet rs = statement.executeQuery(sql);

        return rs;
    }

}

test-servlet.xml

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans     
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/mvc 
        http://www.springframework.org/schema/mvc/spring-mvc.xsd
        http://www.springframework.org/schema/context 
        http://www.springframework.org/schema/context/spring-context.xsd">

   <context:component-scan base-package="com.test, com.test.db" />
   <context:annotation-config />

    <bean id="viewAllData" class="com.test.ViewAllData"/>
    <bean id="dbQuery" class="com.test.db.DBQuery" >
        <property name="start" value="1"/>
    </bean>

    <bean class="org.springframework.context.support.ResourceBundleMessageSource" id="messageSource">
        <property name="basename" value="messages" />
    </bean>

    <bean id="viewResolver" class="org.springframework.web.servlet.view.UrlBasedViewResolver">
        <property name="viewClass" value="org.springframework.web.servlet.view.JstlView" />
        <property name="prefix" value="/WEB-INF/jsp/" />
        <property name="suffix" value=".jsp" />
    </bean>

</beans>

Answer 1

您的代码有多种缺陷。

您的配置存在缺陷，因为不了解注释并将其与XML混合

您应该使用DataSource来处理Connection对象，并在使用

后正确释放它们

控制器

中不应包含SQL处理代码

不应在控制器

中构造HTML

您已经使用带有参数的构造函数定义了 DBQuery类，并使用 @Autowired对此构造函数进行了注释。这意味着Spring将尝试创建 DBQuery的实例(由于您的 <context:component-scan />)，并尝试在您的上下文中找到 String类型的bean。该bean不在那里，因此失败了。

此外，由于组件扫描以及XML中存在一个实例，您最终会得到 DBQuery的多个实例。删除XML配置。组件也可以是 @Service或 @Controller，但不能同时是两者。非 @PropertySource类上的 @Configuration不会执行任何操作。

话虽如此，并假设您主要想使用批注，请先删除 @Autowired构造函数，然后简单地创建 setStart方法。除此以外，它更像是 @Repository。

@Repository
public class DBQuery {

    @Autowired
    private Environment env;
    String dbUsername = env.getProperty("db.username");
    String dbPassword = env.getProperty("db.password");
    String dbUrl = env.getProperty("db.url");
    String start; 

    public ResultSet getAllDataPassport() throws SQLException, ClassNotFoundException{
        Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");  
        Connection conn = DriverManager.getConnection(dbUrl, dbUsername, dbPassword);

        Statement statement = conn.createStatement();
        String sql = "select * from testing_table";
        ResultSet rs = statement.executeQuery(sql);

        return rs;
    }
}

当然，还要从XML中删除 DBQuery bean以及 ViewAllData bean的bean。这些由 <context:component-scan />检测和创建

现在，您应该直接在代码中使用 DriverManager并将其注入到类中，而不是直接使用 DataSource。

将以下内容添加到您的XML配置中。

<context:property-placeholder location="WEB-INF/config.properties" />

<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
    <property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver" />
    <property name="url" value="${db.url}" />
    <property name="username" value="${db.username}" />
    <property name="password" value="${db.password}" />
</bean>

注意:尽管 DriverManagerDataSource是 DataSource，但不要在生产中使用它。在这种情况下，请使用正确的连接池，例如 HikariCP。这里的好处是您可以配置它，并保留 DBQuery不变。

现在，无需注入 Environment和所有属性，只需将 DataSource注入到 DBQuery对象中即可。

@Repository
public class DBQuery {

    private final DataSource dataSource;

    @Autowired    
    public DBQuery(DataSource dataSource) {
        this.dataSource=dataSource;
    }

    public ResultSet getAllDataPassport() throws SQLException {

        Connection conn = this.dataSource.getConnection();
        Statement statement = conn.createStatement();
        String sql = "select * from testing_table";
        ResultSet rs = statement.executeQuery(sql);
        return rs;
    }
}

但是，此代码仍然存在缺陷，因为您没有关闭 Connection和 ResultSet(除非您在控制器中执行此操作，这会使它更加有缺陷)。您的 getAllDataPassport应该应该返回 List对象(或 Passport)的 DataPassport。因此，您需要将控制器的部分处理/转换移至 DBQuery。

为了简化使用JDBC的工作，Spring可能需要使用[ JdbcTemplate]而不是 DataSource来编写代码，因为这将为您管理资源关闭和异常处理。您可以很容易地使用 RowMapper将每一行转换为 Passport对象。

在您的xml中添加以下内容

<bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
    <property name="dataSource" ref="dataSource" />
</bean>

并将其注入您的 DBQuery而不是 DataSource。

@Repository
public class DBQuery {

    private final JdbcTemplate jdbcTemplate;

    @Autowired    
    public DBQuery(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }

    public List<Passport> getAllDataPassport() {

        String sql = "select * from testing_table";
        return this.jdbcTemplate.query(sql, new PassportRowMapper());
    }
}

上面的代码将执行您的查询，获取并关闭资源，并将行转换为 Passport对象。当然，您需要编写 PassportRowMapper才能将每一行转换为 Passport。

public class PassportRowMapper implements RowMapper<Passport> {

    public Passport mapRow(ResultSet rs, int rowNum) throws SQLException {
        Passport p = new Passport();
        p.setNumber(rs.getString(1));
        // further logic to get row information
        return p;
    }
}

注意:请勿在 rs.next中执行 RowMapper，而 JdbcTemplate会解决此问题。您只需要将一行转换为 Passport即可。

现在，您的控制器不再需要进行转换，而不再依赖于SQL。为了进行测试，您现在可以轻松模拟 DBQuery并对 ViewAllData控制器进行单元测试。

@Controller
public class ViewAllData {

    private final DBQuery dbQuery;

    @Autowired
    public ViewAllData(DBQuery dbQuery){
        this.dbQuery = dbQuery;
    }

    @RequestMapping("/viewAllData")
    public ModelAndView viewData() {
        String dataTable;
        List<Passport> passports = dbQuery.getAllDataPassports();
        // List to whatever it needs to be
        return new ModelAndView("viewAllData", "message", dataTable);
    }
}

看起来在您的控制器中，您正在将 List<Passport转换为 String，我担心它包含HTML表。您不应该那样做，在它所属的视图中应该具有这种逻辑。

在控制器中，将项目列表添加到模型中。

    @RequestMapping("/viewAllData")
    public ModelAndView viewData() {
        String dataTable;
        List<Passport> passports = dbQuery.getAllDataPassports();
        // List to whatever it needs to be
        return new ModelAndView("viewAllData", "passports", passports);
    }

现在，在您的视图中，您可以使用JSTL遍历集合并创建HTML表。

<table>
    <c:forEach items="${passports}" var="passport">
        <tr><td>${passport.number}</td><!-- other columns --></tr>
    </c:forEach>
</table>

现在，您已将视图，模型和控制器分离。您现在甚至可以使用同一控制器将其导出为PDF，Excel或JSON。无需更改。

最后的技巧是使用 InternalResourceViewResolver而不是普通的 UrlBasedViewResolver。具有更多功能，自动检测JSTL可以节省一些配置。

<bean id="viewResolver" class="org.springframework.web.servlet.view. InternalResourceViewResolver">
    <property name="prefix" value="/WEB-INF/jsp/" />
    <property name="suffix" value=".jsp" />
</bean>