Question

所以，我有一个简单的REST Web应用程序，如果我的Controller直接调用DAO，JDBC调用工作正常，但如果我的控制器调用另一个代表我调用DAO的类，它会因NullPointerException（NPE）而失败

这是我的控制器：

@Component
@Scope("request")
@Path("/emsrequest")
public class EMSRequest {

    // I'm using this for testing
    @GET
    @Path("/xml/{accountNumber}")
    @Produces({MediaType.TEXT_PLAIN})
    public String requestByAccountNumber_XML(
            @PathParam("accountNumber") String accountNumber) {

        ReqSubTest los = new ReqSubTest();

        return "account (LOS) number is : " + los.testSql(Integer.parseInt(accountNumber)) + "!";
    }
}

这是中间（服务）类：

package com.company.demo.mercury.processmanager.components;

import com.company.demo.pmrws.dao.EMSRequestDaoImpl;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component
public class ReqSubTest {

    @Autowired
    EMSRequestDaoImpl dao = new EMSRequestDaoImpl();

    public int testSql(int quantity){
        return dao.getNextTableIds("sys_process_tbl", quantity);

    }
}

这是DAO实施：

package com.company.demo.pmrws.dao;

import org.apache.log4j.Logger;
import org.springframework.jdbc.core.support.JdbcDaoSupport;

public class EMSRequestDaoImpl extends JdbcDaoSupport {

    private static final Logger logger = Logger.getLogger(EMSRequestDaoImpl.class);

    public int getNextTableIds(String tableName, int quantity) {

        if (logger.isDebugEnabled()) {
            logger.trace("Entering getNextTableIds");
        }

        if (getJdbcTemplate() == null) {
            System.out.println("UH OH!");
        }

        String selectSql = "select next_id "
                + "from sys_key_tbl "
                + "where table_name = ? ";
        String updateSql = "update sys_key_tbl "
                + "set next_id = ? "
                + "where table_name = ? and next_id = ? ";
        int lastId = -1;
        int updateCount = 0;
        while (updateCount == 0) {
            lastId = getJdbcTemplate().queryForInt(selectSql,
                    new Object[]{tableName});
            updateCount = getJdbcTemplate().update(updateSql,
                    new Object[]{lastId + quantity, tableName, lastId});
        }

        if (logger.isDebugEnabled()) {
            logger.trace("Leaving getNextTableIds");
        }
        return lastId + 1;
    }
}

应用程序上下文XML：

<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-2.5.xsd
   http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd">
    <context:component-scan base-package="com.company.demo.pmrws"/>

    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
          destroy-method="close">
        <property name="driverClassName" value="com.sybase.jdbc3.jdbc.SybDataSource" />
        <property name="url"
                  value="jdbc:sybase:Tds:blah:10240/BLAH_DB1" />
        <property name="username" value="blah" />
        <property name="password" value="blah" />
    </bean>

    <bean id="dataSourceMain" class="org.apache.commons.dbcp.BasicDataSource"
          destroy-method="close">
        <property name="driverClassName" value="com.sybase.jdbc3.jdbc.SybDataSource" />
        <property name="url"
                  value="jdbc:sybase:Tds:blah:10240/BLAH_DB2" />
        <property name="username" value="blah" />
        <property name="password" value="blah" />
    </bean>
    </bean>

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

    <bean id="emsResponseDao" class="com.company.demo.pmrws.dao.EMSResponseDaoImpl">
        <property name="dataSource" ref="dataSource" />
    </bean>

    <bean id="emsStatusDao" class="com.company.demo.pmrws.dao.EMSStatusDaoImpl">
        <property name="dataSource" ref="dataSourceMain" />
    </bean>

<!--    <bean id="collateralSybaseEmsDao" class="com.company.demo.dao.CollateralSybaseEmsDaoImpl">
        <property name="dataSource" ref="dataSource" />
    </bean>

    <bean id="collateralSybaseDao" class="com.company.demo.dao.CollateralSybaseDaoImpl">
        <property name="dataSource" ref="dataSource" />
    </bean>-->

    <bean id="emsRequestDao" class="com.company.demo.pmrws.dao.EMSRequestDaoImpl">
        <property name="dataSource" ref="dataSource" />
    </bean>

    <context:component-scan base-package="com.company.demo.mercury.processmanager.components" />

</beans>

我错过了什么？顺便说一句，这是Spring 2.5。

Answer 1

这是因为ReqSubTest los = new ReqSubTest();创建了一个新的普通java Object实例而不是Spring Bean，因此没有任何内容注入los实例。

解决它的三种方法。

代替ReqSubTest los = new ReqSubTest();通过Spring注入los，但这要求EMSRequest也是一个Spring bean

示例：

@Component public class EMSRequest {

    @Autowire ReqSubTest los;

    public String requestByAccountNumber_XML(@PathParam("accountNumber") String accountNumber) {
        return "account (LOS) number is : " + los.testSql(Integer.parseInt(accountNumber)) + "!";
    } 
}

而不是ReqSubTest los = new ReqSubTest();使用ReqSubTest los = springApplicationContext.getBean(ReqSubTest.class)
如果您使用真正的AspectJ，那么您可以添加@Configurable然后Spring注入其他bean即使通过new创建实例（需要通过<context:spring-configured />启用） - 您可以将注释添加到EMSRequest，然后在第一项中使用正常注入，例如suggeted，或将其添加到ReqSubTest

Answer 2

我想我已经找到了问题所在。问题出在您的服务类ReqSubTest中。

你已经在那里自动安装了DAO类，但你不应该在那里初始化它。所以只需删除DAO声明的初始化部分，就可以了。所以现在你在服务类中的声明将如下所示。

@Autowired
private EMSRequestDaoImpl dao;

在您的控制器中，您还需要自动装配Service类。并且不要在函数本身中创建它的新对象。

@Autowired
private ReqSubTest service;

希望这会对你有所帮助。欢呼声。

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