Question

你可以帮帮我吗？ 1.My Dao

package user.dao.impl;

import java.sql.ResultSet;
import java.sql.SQLException;

import javax.sql.DataSource;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.core.RowCallbackHandler;
import org.springframework.jdbc.datasource.DataSourceTransactionManager;
import user.domain.DboBean;

public class DboDao {
    private DataSourceTransactionManager transactionManager;
    private JdbcTemplate jdbcTemplate;

    public DboDao() {
        // TODO Auto-generated constructor stub
        super();
        DataSource datatSource = transactionManager.getDataSource();
        jdbcTemplate = new JdbcTemplate(datatSource);
    }

//Spring setter injector used
public void setTransactionManager(DataSourceTransactionManager transactionManager){
    this.transactionManager = transactionManager;
}


public DboBean read() {//String dboId
    // TODO Auto-generated method stub
    String sql = "SELECT ins_ID, ins_name FROM da_tracking "
            + "WHERE ins_ID = 3";
    final Object[] params = new Object[] {};//dboId

    //Creating object being queried
    final DboBean dboBean = new DboBean();      
    //Process query Results
    jdbcTemplate.query(sql, params, new RowCallbackHandler(){
        public void processRow(ResultSet rs) throws SQLException{
            dboBean.setDboId(rs.getString("dboId"));    
        }

    });
    return dboBean;//returns queried objects
}
}

我的豆子：

 package user.domain;

 public class DboBean {

    private String dboId;
    private String dboDevName;

    public DboBean(){
        this.setDboId(dboId);
        this.setDboDevName(dboDevName);     
    }

    public String getDboId() {
        return dboId;
    }

    public void setDboId(String dboId) {
        this.dboId = dboId;
    }

    public String getDboDevName() {
        return dboDevName;
    }

    public void setDboDevName(String dboDevName) {
        this.dboDevName = dboDevName;
    }
 }

我的春天：

<?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:lang="http://www.springframework.org/schema/lang"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.1.xsd
http://www.springframework.org/schema/lang http://www.springframework.org/schema/lang/spring-lang-3.1.xsd">

<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
    destroy-method="close">
    <property name="driverClassName" value="net.sourceforge.jtds.jdbc.Driver" />
    <property name="url"
        value="jdbc:jtds:sqlserver://localhost:1433;databaseName=XYDB" />
    <property name="username" value="user" />
    <property name="password" value="xyz" />            
</bean>

<bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
    <property name="dataSource" ref="dataSource" />
</bean>

<bean id="objDbo" class="user.dao.impl.DboDao">
    <property name="transactionManager" ref="transactionManager" />
</bean>

</beans>

我的Junit：

package user.dao.JUnitTest;

import junit.framework.Test;
import junit.framework.TestCase;
import junit.framework.TestSuite;

import org.apache.log4j.xml.DOMConfigurator;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.FileSystemXmlApplicationContext;
import java.lang.Object;

import user.dao.impl.DboDao;
import user.domain.DboBean;


public class JUnitDaoTest extends TestCase {
private static final String OID = "dboId";
private static final String DDN = "dboDevName";
protected static ApplicationContext appContext;
private DboDao objDao;

public JUnitDaoTest(String arg) {
    super(arg);
}

public static Test suite(){
    TestSuite suite = new TestSuite();
    suite.addTest(new JUnitDaoTest("testDboDAO"));
    return suite;       
}

public void setUp() throws Exception{
    init();
    objDao =  (DboDao) getBean("objDao");
}

public static void main(String[] args){
    junit.textui.TestRunner.run(suite());
}
//@Override
public synchronized void init(){
    if (appContext == null){
        try{
            String path = System.getProperty("user.dir");
            String slash = System.getProperty("file.separator");

            String configDir = path + slash + "config" + slash;
            DOMConfigurator.configure(configDir +  "log4j.xml");

            appContext = new FileSystemXmlApplicationContext(new String[] {configDir + "appContext.xml"});
        }catch(Exception e){
            System.err.println(e.getMessage());
        }
    }
}

protected Object getBean(String beanName){
    return appContext.getBean(beanName);
}


public void testDboDAO(){
    DboBean record = new DboBean();
    record.setDboId(OID);//setDboId(dboId);
    record.setDboDevName(DDN);



    DboBean bean = objDao.read();
    assertEquals(DDN, bean.getDboDevName());
    System.out.println("User selected [" + bean.getDboId() + ", " + bean.getDboDevName() + 
            "]");

    //objDao.delete(dboId);
    //bean = objDao.read(dboId);
    //assertEquals(null, bean.getDboDevName());
    //System.out.println("User is deleted [" + bean.getDboId() + ", " + bean.getDboDevName() + 
        //  "]");

}

}

我收到此错误：在文件[... \ config \ appContext.xml]中定义名为'objDbo'的bean时出错：bean的实例化失败;嵌套异常是org.springframework.beans.BeanInstantiationException：无法实例化bean类[user.dao.impl.DboDao]：构造函数抛出异常;嵌套异常是java.l

你有个主意吗？团块

Answer 1

stacktrace将解释确切的问题，它将在你切断的堆栈跟踪的“嵌套异常是java.l ...”之后的任何内容中。阅读整个错误消息。

如果我猜测，你的DboDao类在构造函数中有一个空指针异常，因为你指的是尚未设置的字段transactionManager。

我建议编写这个DboDao类的单元测试 - 它根本不涉及Spring - 来测试当你调用new DboDao()时会发生什么。

另外，您可能会发现让DAO类扩展Spring实用程序类JdbcDaoSupport很方便。

Answer 2

在构造函数中使用DataSourceTransactionManager时，未设置它。当Spring设置您的上下文时，这将导致NPE。

除了设置JdbcTemplate之外，您可以选择仅依赖注入JdbcTemplate，因为您的事务管理器未被使用。无论出于何种原因，如果您不想配置JdbcTemplate，可以使用init method来构建它（因为它将在Spring提供所有依赖项后调用）。

Answer 3

public class DboDao {
private DataSourceTransactionManager transactionManager;
private JdbcTemplate jdbcTemplate;

public DboDao() {
    // TODO Auto-generated constructor stub
    super();
    // problem exists here, as transactionManager is not set yet and
    // you are using Setter Based injection so `NPE`
    // you can move this code in setter method of transactionManager, to make it work. 
    DataSource datatSource = transactionManager.getDataSource(); 
    jdbcTemplate = new JdbcTemplate(datatSource);
}.............

另外，我在你的代码中看到了错误的东西。在服务层使用事务管理器。并在DboDao中注入dataSource。并创建jdbcTemplate，如下所示：

public class DboDao {
private DataSource dataSource;  // either use @Autowire or provide xml config
private JdbcTemplate jdbcTemplate;

public DboDao() {        
    super();        
}
....// getter and setter for jdbcTemplate and dataSource

public void setDataSource(DataSource dataSource) {
    this.dataSource = dataSource;
    jdbcTemplate = new JdbcTemplate(dataSource);
}

查看您的配置文件，如果您想让您的应用运行：在setter方法中初始化dataSource和jdbcTemplate，就像使用基于setter的注入一样。

public class DboDao {
    private DataSourceTransactionManager transactionManager;
    private JdbcTemplate jdbcTemplate;

    public DboDao() {
        super();            
    }

//Spring setter injector used
public void setTransactionManager(DataSourceTransactionManager transactionManager){
    this.transactionManager = transactionManager;
    // moved code from constructor
    DataSource datatSource = transactionManager.getDataSource(); 
    jdbcTemplate = new JdbcTemplate(datatSource);
}

在文件..xml中定义名为“..”的bean时出错

3 个答案: