如何执行Spring JDBC连接并检索数据？

Question

I am creating a Web Application using Java and Spring. I need to connect to MySQL database and retrieve data in Servlet to display in my JSP page. I searched lot and got many examples to connect to database, but nothing works for me

Here is my applicationContext.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:aop="http://www.springframework.org/schema/aop"
    xmlns:tx="http://www.springframework.org/schema/tx" xmlns:batch="http://www.springframework.org/schema/batch"
    xmlns:jdbc="http://www.springframework.org/schema/jdbc" xmlns:context="http://www.springframework.org/schema/context"

    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
    http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-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/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc-3.1.xsd    
    http://www.springframework.org/schema/batch http://www.springframework.org/schema/batch/spring-batch-2.1.xsd
    http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd">

    <!-- 1) USE ANNOTATIONS TO CONFIGURE SPRING BEANS -->
    <context:component-scan base-package="com.app.any" />
    <!-- 2) DATASOURCE, TRANSACTION MANAGER AND JDBC TEMPLATE -->
    <bean id="dataSource"
        class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="com.mysql.jdbc.Driver" />
        <property name="url" value="jdbc:mysql://localhost:3306/mydatabase" />
        <property name="username" value="root" />
        <property name="password" value="admin" />
       <bean>
       <bean id="transactionManager"
        class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
        <property name="dataSource" ref="dataSource" />
    </bean>
    <tx:annotation-driven transaction-manager="transactionManager" />

    <bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
        <property name="dataSource" ref="dataSource" />
    </bean>
        <bean id="getTargetFields"  class="com.app.myapp.controllers.controllerClasses.GetTargetFields">
       </bean>
    <beans

From my servlet I am calling a class called GetTargetFields . In that class I want to pass the query and retrieve the data. But I don't know how to pass. Tried many examples using the query() method of JdbcTemplate class. But it is showing error as I dont know which class to pass and what is the return type. Its return type is Object . I tried ResultSet but showed error.

What I want is in my GetTargetFields class I want to pass a select query and return the result and I want to save the result in ResultSet.

public class GetTargetFields
{


    public void getTargetField()
    {
            // What code should be here?
    }

}

Can anyone help me to code? Thanks

UPDATE 1

public class GetTargetFields
{
    private JdbcTemplate jdbcTemplate;
    private DataSource dataSource;

    public static ResultSet rs=null;

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

    public ResultSet getTargetField() // I know the code is wrong. But I tried this
    {
         ResultSet rs=jdbcTemplate.query("SELECT * from employee",
            ResultSet); //shows error. I want to get the result in ResultSet 
                //Or how the data will be stored in *Collector* and I can access each column fields?
     return rs;
    }

}

Answer 1

You are not injecting or autowiring the jdbcTemplate instance into your GetTargetFields class. It should be either injected like this.

<bean id="getTargetFields"  class="com.app.myapp.controllers.controllerClasses.GetTargetFields">
         <property name="jdbcTemplate" ref="jdbcTemplate" />
</bean>

or autowire it using the @Autowired annotation.

In the current case even though you have a setter method for data source you are neither injecting that as well. You do not need to create a new instance of JdbcTemplate as you have already done the bean definition in app-context file and Spring will instantiate it for you. So the correct implementation should be to inject the jdbcTemplate

Answer 2

You need to use the following syntax

jdbcTemplate.query("", new ResultSetExtractor<Object>() {

    @Override
    public Object extractData(ResultSet rs) throws SQLException,
            DataAccessException {
        //do what ever you want to do with rs
        return null;
    }
});

Answer 3

You will have to either inject your jdbcTemplate object manually using the following:

<bean id="getTargetFields" class="com.app.myapp.controllers.controllerClasses.GetTargetFields">
    <property name="jdbcTemplate" ref="jdbcTemplate" />  
</bean>

Then, you can change the class that injects the jdbcTemplate object to:

public class GetTargetFields {
    private JdbcTemplate jdbcTemplate;
    ...
}

Or use the @Autowired and @Repository annotations.

Please see the first half of the following Spring reference which shows how can use those two annotations that would take away much of the complexity: http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/jdbc.html

Answer 4

You have the following method in your GetTargetFields class

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

This means that, during your bean initialization, you can give a datasource as a property which will be injected by spring framework.

<bean id="getTargetFields" class="com.app.myapp.controllers.controllerClasses.GetTargetFields">
    <property name="dataSource" ref="dataSource">    
</bean>