我昨晚花了很多时间试图弄清楚这一点。我有一个 HSQLDB 服务器正在运行，我可以使用 JDBC 驱动程序连接到它。任务的下一部分是做同样的事情，但使用 Spring 框架。我声明了我的 bean，创建了我的 DAO 类，但程序没有连接到服务器。由于这是我们第一次使用 JdbcTemplate，我们不应该进行自动装配。这是我拥有的文件：
JdbcUserDAO
public class JdbcUserDAO extends JdbcDaoSupport
implements UserDAO {
public User getUserWithId(int id) {
return new User(1,"gamda","test");
}
public int howManyUsers() {
JdbcTemplate test = getJdbcTemplate();
System.out.println("Got template");
try {
getConnection();
System.out.println("Got connection");
} catch (Exception e) {
System.out.println("Not connecting");
}
int result = test.queryForInt("select count from users");
System.out.println("Query success");
return result;
}
}
beans.xml（与我的 .java 文件在同一个文件夹中，如果有区别的话）
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="userDAO" class="com.project2.db.JdbcUserDAO">
<property name="dataSource" ref="dataSource"/>
</bean>
<bean id="questionDAO" class="com.project2.db.JdbcQuestionDAO">
<property name="jdbcTemplate" ref="jdbcTemplate"/>
</bean>
<bean id="answerDAO" class="com.project2.db.AnswerDAO">
<property name="jdbcTemplate" ref="jdbcTemplate"/>
</bean>
<bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
<property name="dataSource" ref="dataSource"/>
</bean>
<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
destroy-method="close">
<property name="driverClassName" value="org.hsqldb.jdbc.JDBCDriver"/>
<property name="url" value="jdbc:hsqldb:hsql://localhost/cpsc476;ifexists=true"/>
<property name="username" value="SA"/>
<property name="password" value="Passw0rd"/>
</bean>
</beans>
蚂蚁的build.xml：
<project
name="DB_Access"
default="compile"
xmlns:artifact="antlib:org.apache.maven.artifact.ant">
<target name="init">
<mkdir dir="classes" />
</target>
<target name="clean">
<delete dir="classes" />
<delete dir="jar" />
</target>
<target name="compile" depends="init">
<javac srcdir="src"
destdir="classes">
<classpath refid="dependency.classpath" />
</javac>
</target>
<target name="run" depends="compile">
<java classname="com.project2.db.ListQuestionsAndAnswers">
<classpath>
<path refid="dependency.classpath" />
<path location="classes/" />
</classpath>
</java>
</target>
<target name="jar" depends="compile">
<mkdir dir="jar" />
<jar destfile="jar/db.jar" basedir="classes">
<manifest>
<attribute name="Main-Class" value="com.project2.db.dbCon" />
</manifest>
</jar>
</target>
<artifact:dependencies
pathId="dependency.classpath"
filesetId="dependency.fileset">
<dependency
groupId="org.springframework"
artifactId="spring-jdbc"
version="3.2.4.RELEASE" />
<dependency
groupId="org.springframework"
artifactId="spring-beans"
version="3.2.4.RELEASE"/>
<dependency
groupId="org.springframework"
artifactId="spring-context"
version="3.0.2.RELEASE"/>
<dependency
groupId="org.hsqldb"
artifactId="hsqldb"
version="2.3.0" />
<dependency
groupId="commons-dbcp"
artifactId="commons-dbcp"
version="1.4" />
</artifact:dependencies>
</project>
我正在使用的测试类：阅读提供的教程后编辑
public class ListQuestionsAndAnswers {
public static int main( String[] args ) {
ApplicationContext appContext = new ClassPathXmlApplicationContext(
"beans.xml");
JdbcUserDAO test = (JdbcUserDAO) appContext.getBean("userDAO");
int answer = test.howManyUsers();
System.out.println(answer);
return 0;
}
}
当我执行“ant run”时，这是输出：Edited because it's a new error
>[java] org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userDAO' defined in class path resource [beans.xml]: Initialization of bean failed; nested exception is java.lang.NoSuchFieldError: NULL
>[java] at org.apache.tools.ant.taskdefs.ExecuteJava.execute(ExecuteJava.java:194)
>[java] at org.apache.tools.ant.taskdefs.Java.run(Java.java:771)
>[java] at org.apache.tools.ant.taskdefs.Java.executeJava(Java.java:221)
>[java] at org.apache.tools.ant.taskdefs.Java.executeJava(Java.java:135)
>[java] at org.apache.tools.ant.taskdefs.Java.execute(Java.java:108)
>[java] at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:292)
>[java] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
>[java] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
>[java] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
>[java] at java.lang.reflect.Method.invoke(Method.java:606)
>[java] at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:106)
>[java] at org.apache.tools.ant.Task.perform(Task.java:348)
>[java] at org.apache.tools.ant.Target.execute(Target.java:435)
>[java] at org.apache.tools.ant.Target.performTasks(Target.java:456)
>[java] at org.apache.tools.ant.Project.executeSortedTargets(Project.java:1393)
>[java] at org.apache.tools.ant.Project.executeTarget(Project.java:1364)
>[java] at org.apache.tools.ant.helper.DefaultExecutor.executeTargets(DefaultExecutor.java:41)
>[java] at org.apache.tools.ant.Project.executeTargets(Project.java:1248)
>[java] at org.apache.tools.ant.Main.runBuild(Main.java:851)
>[java] at org.apache.tools.ant.Main.startAnt(Main.java:235)
>[java] at org.apache.tools.ant.launch.Launcher.run(Launcher.java:280)
>[java] at org.apache.tools.ant.launch.Launcher.main(Launcher.java:109)
>[java] Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userDAO' defined in class path resource [beans.xml]: Initialization of bean failed; nested exception is java.lang.NoSuchFieldError: NULL
>[java] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:529)
>[java] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:458)
>[java] at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:295)
>[java] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:223)
>[java] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:292)
>[java] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
>[java] at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:628)
>[java] at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:872)
>[java] at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:423)
>[java] at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
>[java] at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
>[java] at com.project2.db.ListQuestionsAndAnswers.main(Unknown Source)
>[java] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
>[java] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
>[java] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
>[java] at java.lang.reflect.Method.invoke(Method.java:606)
>[java] at org.apache.tools.ant.taskdefs.ExecuteJava.run(ExecuteJava.java:217)
>[java] at org.apache.tools.ant.taskdefs.ExecuteJava.execute(ExecuteJava.java:152)
>[java] ... 21 more
>[java] Caused by: java.lang.NoSuchFieldError: NULL
>[java] at org.springframework.expression.TypedValue.<clinit>(TypedValue.java:31)
>[java] at org.springframework.expression.spel.support.StandardEvaluationContext.setRootObject(StandardEvaluationContext.java:82)
>[java] at org.springframework.expression.spel.support.StandardEvaluationContext.<init>(StandardEvaluationContext.java:71)
>[java] at org.springframework.context.expression.StandardBeanExpressionResolver.evaluate(StandardBeanExpressionResolver.java:124)
>[java] at org.springframework.beans.factory.support.AbstractBeanFactory.evaluateBeanDefinitionString(AbstractBeanFactory.java:1312)
>[java] at org.springframework.beans.factory.support.BeanDefinitionValueResolver.evaluate(BeanDefinitionValueResolver.java:225)
>[java] at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:312)
>[java] at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:107)
>[java] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1387)
>[java] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1128)
>[java] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:519)
>[java] ... 38 more
>[java] Java Result: -1
所以我知道我的 JdbcTemplate 不为空，但它无法连接到数据库，我不知道如何检查连接或使其连接。