尝试访问数据库时导致NullPointerException

Question

This is the method which is giving me the NullPointerException . I have narrowed it down to the line which queries the database.

The code does not reach the second logger. The exception is thrown before it prints out.

UPDATE: I just tested the jdbcTemplate and it is what is NULL.

public boolean usernameVerificationProcessService(String string){
    HomeController.logger.info("In method usernameVerificationProcessService in UIDao.");
    HomeController.logger.info("Attention: " + string);
    boolean result = false;
    String sql = "select count(*) from users where username = ?";
    int count = this.jdbcTemplate.queryForObject(sql, new Object[]{string}, java.lang.Integer.class);
    HomeController.logger.info("Attention: " + count);
    if(count == 0) {
        result = true;
    }
    return result;
}

This is the config file description. I am using a BasicDataSource and MySQL.

<beans:bean id="dataSource" destroy-method="close" class="org.apache.commons.dbcp.BasicDataSource">
    <beans:property name="driverClassName" value="com.mysql.jdbc.Driver"/>
    <beans:property name="url" value="jdbc:mysql://localhost:3306"/>
    <beans:property name="username" value="test"/>
    <beans:property name="password" value="test"/>
    <beans:property name="initialSize" value="2" />
    <beans:property name="maxActive" value="5" />
</beans:bean>

Answer 1

Do you forget to inject the jdbcTemplate into the object?

public class DBaseAccess {
    private JdbcTemplate jdbcTemplate;
    public void setJdbcTemplate(JdbcTemplate jdbcTemplate) {
        this.jdbcTemplate = jdbcTemplate;
    }
  .......
}

You must inject the jdbcTemplate to the object in your spring config file (applicationContext.xml)

 <bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
    <property name="dataSource" ref="dataSource" />
 </bean>
 <bean id="dBaseAccess" class="coc.taf.dbase.DBaseAccess">
    <property name="jdbcTemplate" ref="jdbcTemplate" />
 </bean>

Answer 2

You never check the string parameter for null . I guess it fails with NPE.