Spring JdbcTemplate框架搭建及其增删改查使用指南

Spring JdbcTemplate框架搭建及其增删改查使用指南

前言：

本文指在介绍spring框架中的JdbcTemplate类的使用方法，涉及基本的Spring反转控制的使用方法和JDBC的基本概念。目标是使读者能够对JdbcTemplate快速地掌握和使用。

原创不易，转载请注明出处：Spring JdbcTemplate框架搭建及其增删改查使用指南

http://www.zui（#￥#￥#￥#￥#￥#）daima.com/share/1724429678644224.htm

代码下载地址：http://www.zui（#￥#￥#￥#￥#￥#）daima.com/share/1724429678644224.htm

不明白为什么，zui（#￥#￥#￥#￥#￥#）daima会被博客园说成是违禁内容，没办法，原创的连接，我只能在zui后面加入了特殊符号。

准备：

1. Spring的基本概念

Spring框架核心的思想就是建立一个Java对象的大工厂，用户只要给工厂一个指令，工厂就能将用户需要的对象根据配置文件组装好返还给用户。用户需要做的许多工作则可以写成简单的配置文件。

2. 丑陋的JDBC代码

Connection con = null;
PreparedStatement pStmt = null;
ResultSet rs = null;
try {
     con = ods.getConnection();
     String sql = "select * from admin";
     pStmt = con.prepareStatement(sql);
     rs = pStmt.executeQuery();
     while (rs.next()) {
     }
} catch (Exception ex) {
     try {
          con.rollback();
     } catch (SQLException sqlex) {
          sqlex.printStackTrace(System.out);
     }
     ex.printStackTrace();
} finally {
     try {
          rs.close();
          pStmt.close();
          con.close();
     } catch (Exception e) {
          e.printStackTrace();
     }
}

以上是常见的JDBC代码，简单的select语句也需要冗长的出错处理，并且每个函数都不断地重复同样的代码。

3. JdbcTemplate的作用

JdbcTemplate正是为了减少上述繁琐的代码而设计出来的。它是对JDBC的一种封装，抽象我们常用的一些方法。Simple and Stupid就是它的目标。下面是完成了刚才JDBC代码同样功能的JdbcTemplate的代码：

String sql = "select * from admin";

jdbcTemplate.query(sql,new RowCallbackHandler() {

         public void processRow(ResultSet rs) throws SQLException {  

                }

            } );

环境搭建：

1. 数据库的配置

本文使用Mysql数据库，新建表admin：

CREATE TABLE `admin` (
  `ID` bigint(20) unsigned NOT NULL auto_increment,
  `NAME` varchar(100) NOT NULL,
  `PASSWORD` varchar(200) NOT NULL,
  PRIMARY KEY  (`ID`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

　　

2. Spring配置

JdbcTemplate的使用需要有DataSource的支持，所以在配置文件中，我们首先要配置一个OracleDataSource，然后在将这个DataSource配置到JdbcTemplate里。接着将JdbcTemplate配置进DAO层，最后将DAO配置进Model层。简要的关系如下：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN"
    "http://www.springframework.org/dtd/spring-beans.dtd">
<beans>
	<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/zuidaima_admin?useUnicode=true&characterEncoding=utf-8" />
		<property name="username" value="root" />
		<property name="password" value="111111" />
	</bean>

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

	<bean id="userDao" class="com.zuidaima.dao.impl.UserDaoImpl">
		<property name="jdbcTemplate">
			<ref bean="jdbcTemplate" />
		</property>
	</bean>

	<bean id="user" class="com.zuidaima.model.User">
		<property name="dao">
			<ref bean="userDao" />
		</property>
	</bean>

</beans>

3. 项目截图：

使用方法：

　　1.查找

　　多行查询：

class UserRowMapper implements RowMapper {

        public Object mapRow(ResultSet rs,int index) throws SQLException

        {

            User u = new User();

            u.setId(rs.getString("ID"));

            u.setName(rs.getString("Name"));

            u.setPassword(rs.getString("Password"));

            return u;

        }

    }

public List select(String where)

    {

        List list;      

        String sql = "select * from admin "+where;      

        list = jdbcTemplate.query(sql,new RowMapperResultReader(new UserRowMapper()));

        return list;

    }

List最终返回的是满足条件的User队列。

 

单行查询：

public User selectById(String id){

    String sql = "select * from admin where id=?";

    final User u = new User();

    final Object[] params = new Object[] {id};

    jdbcTemplate.query(sql, params, new RowCallbackHandler(){

                        public void processRow(ResultSet rs) throws SQLException {

                                 u.setId(rs.getString("ID"));

                                 u.setName(rs.getString("NAME"));

                                 u.setPassword(rs.getString("PASSWORD"));

                        }                    

    });        

    return u;

}

2.      插入

public void insert(User u)

{

     String sql = "insert into admin (ID,NAME,PASSWORD) values (admin_id_seq.nextval,?,?)";

     Object[] params = new Object[] {

                                                u.getName(),

                                                u.getPassword() };

     jdbcTemplate.update(sql,params);

}

　

admin_id_seq.nextval为Oracle设置好的序列，问号“?”被params里的数据依次替代，最终执行sql。

 

3.      修改

非常简单：

public void update(String how)

{

        jdbcTemplate.update(how);

    }

运行截图

数据库截图

----------------  个人补充（抱明月）  ------------------

jdbc中，查询应该是最复杂的。jdbctemplate也一样

jdbctemplate中，查询，首先是先需要实现【RowCallBackHandler】或者【RowMapper】，写出一个将ResultSet转换成Bean的转换器。

例如：上面例子中的代码：

class UserRowMapper implements RowMapper {

        public Object mapRow(ResultSet rs,int index) throws SQLException

        {

            User u = new User();

            u.setId(rs.getString("ID"));

            u.setName(rs.getString("Name"));

            u.setPassword(rs.getString("Password"));

            return u;

        }

    }

这样的转换器，可以单独写成一个类，也可以直接写在 Dao层类或者Bean类的内部。

实现【RowCallBackHandler】或者【RowMapper】，是有区别的。

简单来说，大数据量应该使用【RowCallBackHandler】，因为他是分批的查询数量。（无返回值）

小数据量应该使用【RowMapper】，因为他是一次性将所有数据从数据库中读取出来，然后加载到内存中，如果数据量很大，那么很容易占用很大内存甚至内存溢出。（有返回值）

还有查询分为 多行查询和单行查询。

多行查询

多行查询，需要用到上面提到的【RowCallBackHandler】或者【RowMapper】。

单行查询，是具有自动转换的功能的，可以在查询的时候，直接输入Bean类的class类，可以自动转换。多行的不能自动转。

还有QueryForXXX的方法，好像是如果没有找到数据，会出现异常

还有当把【RowCallBackHandler】或者【RowMapper】定义成通用的类的时候，一般，都会做所有字段的转换。

但是查询语句中往往只查询部分字段，那么【RowCallBackHandler】或者【RowMapper】中去取没有数据的字段的时候，会出现异常。

所以最好需要判断下：

    public boolean isExistColumn(ResultSet rs, String columnName) {
        try {
            if (rs.findColumn(columnName) > 0) {
                return true;
            }
        } catch (SQLException e) {
            return false;
        }

        return false;
    }

　　

if (isExistColumn(resultSet, "id")) {
                    product.setId(resultSet.getInt("id"));
                }

　　

Spring JDBCTemplate结合DButils的自动转换的类，实现自动转换

转载自：http://www.oschina.net/code/snippet_1029551_27218?spm=0.0.0.0.Wr5erR

在使用String的jdbcTemplate时候，想要将返回结果ResultSet映射到一个javaBean非常麻烦，要么自己先写一个类继承ResultSetExtractor 或者 RowMapper，要么就在调用query(sql, args, new XXX<T>(){})使用内部类的方式来写，感觉都比较麻烦，后来参考了apche的DBUtils，搞了个反射，只要是符合javaBean规范的bean都可以自动将rs中的返回结果映射成对应的javaBean

1. [代码]MyJdbcTemplate继承自Spring的JdbcTemplate，主要是增加了queryForBean方法

package com.uncle5.pubrub.dal;

import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;

import org.springframework.dao.DataAccessException;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.core.ResultSetExtractor;
import org.springframework.jdbc.core.RowMapper;

public class MyJdbcTemplate extends JdbcTemplate {

    /**
     * 此处是借用DBUtils中的对应类，同时增加了对Annotation的支持
     */
    private final BasicRowProcessor convert = new BasicRowProcessor();

    public <T> T queryForBean(String sql, final Class<T> beanType) {
        return query(sql, new ResultSetExtractor<T>() {

            @Override
            public T extractData(ResultSet rs) throws SQLException,
                    DataAccessException {
                return rs.next() ? convert.toBean(rs, beanType) : null;
            }
        });
    }

    public <T> T queryForBean(String sql, final Class<T> beanType,
            Object... args) {
        return query(sql, args, new ResultSetExtractor<T>() {

            @Override
            public T extractData(ResultSet rs) throws SQLException,
                    DataAccessException {
                return rs.next() ? convert.toBean(rs, beanType) : null;
            }
        });
    }

    public <T> List<T> queryForBeanList(String sql, final Class<T> beanType) {
        return query(sql, new RowMapper<T>() {

            @Override
            public T mapRow(ResultSet rs, int rowNum) throws SQLException {
                return convert.toBean(rs, beanType);
            }
        });
    }

    public <T> List<T> queryForBeanList(String sql, final Class<T> beanType,
            Object... args) {
        return query(sql, args, new RowMapper<T>() {

            @Override
            public T mapRow(ResultSet rs, int rowNum) throws SQLException {
                return convert.toBean(rs, beanType);
            }
        });
    }
}

　　

2. [代码]BasicRowProcessor，此类为DBUtils中的原声类

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.uncle5.pubrub.dal;

import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.HashMap;
import java.util.List;
import java.util.Locale;
import java.util.Map;

import org.apache.commons.dbutils.RowProcessor;

/**
 * Basic implementation of the <code>RowProcessor</code> interface.
 *
 * <p>
 * This class is thread-safe.
 * </p>
 *
 * @see RowProcessor
 */
public class BasicRowProcessor {

    /**
     * The default BeanProcessor instance to use if not supplied in the
     * constructor.
     */
    private static final BeanProcessor defaultConvert = new BeanProcessor();

    /**
     * The Singleton instance of this class.
     */
    private static final BasicRowProcessor instance = new BasicRowProcessor();

    /**
     * Returns the Singleton instance of this class.
     *
     * @return The single instance of this class.
     * @deprecated Create instances with the constructors instead. This will be
     *             removed after DbUtils 1.1.
     */
    @Deprecated
    public static BasicRowProcessor instance() {
        return instance;
    }

    /**
     * Use this to process beans.
     */
    private final BeanProcessor convert;

    /**
     * BasicRowProcessor constructor. Bean processing defaults to a
     * BeanProcessor instance.
     */
    public BasicRowProcessor() {
        this(defaultConvert);
    }

    /**
     * BasicRowProcessor constructor.
     *
     * @param convert
     *            The BeanProcessor to use when converting columns to bean
     *            properties.
     * @since DbUtils 1.1
     */
    public BasicRowProcessor(BeanProcessor convert) {
        super();
        this.convert = convert;
    }

    /**
     * Convert a <code>ResultSet</code> row into an <code>Object[]</code>. This
     * implementation copies column values into the array in the same order
     * they're returned from the <code>ResultSet</code>. Array elements will be
     * set to <code>null</code> if the column was SQL NULL.
     *
     * @see org.apache.commons.dbutils.RowProcessor#toArray(java.sql.ResultSet)
     * @param rs
     *            ResultSet that supplies the array data
     * @throws SQLException
     *             if a database access error occurs
     * @return the newly created array
     */
    public Object[] toArray(ResultSet rs) throws SQLException {
        ResultSetMetaData meta = rs.getMetaData();
        int cols = meta.getColumnCount();
        Object[] result = new Object[cols];

        for (int i = 0; i < cols; i++) {
            result[i] = rs.getObject(i + 1);
        }

        return result;
    }

    /**
     * Convert a <code>ResultSet</code> row into a JavaBean. This implementation
     * delegates to a BeanProcessor instance.
     *
     * @see org.apache.commons.dbutils.RowProcessor#toBean(java.sql.ResultSet,
     *      java.lang.Class)
     * @see org.apache.commons.dbutils.BeanProcessor#toBean(java.sql.ResultSet,
     *      java.lang.Class)
     * @param <T>
     *            The type of bean to create
     * @param rs
     *            ResultSet that supplies the bean data
     * @param type
     *            Class from which to create the bean instance
     * @throws SQLException
     *             if a database access error occurs
     * @return the newly created bean
     */
    public <T> T toBean(ResultSet rs, Class<T> type) throws SQLException {
        return this.convert.toBean(rs, type);
    }

    /**
     * Convert a <code>ResultSet</code> into a <code>List</code> of JavaBeans.
     * This implementation delegates to a BeanProcessor instance.
     *
     * @see org.apache.commons.dbutils.RowProcessor#toBeanList(java.sql.ResultSet,
     *      java.lang.Class)
     * @see org.apache.commons.dbutils.BeanProcessor#toBeanList(java.sql.ResultSet,
     *      java.lang.Class)
     * @param <T>
     *            The type of bean to create
     * @param rs
     *            ResultSet that supplies the bean data
     * @param type
     *            Class from which to create the bean instance
     * @throws SQLException
     *             if a database access error occurs
     * @return A <code>List</code> of beans with the given type in the order
     *         they were returned by the <code>ResultSet</code>.
     */
    public <T> List<T> toBeanList(ResultSet rs, Class<T> type)
            throws SQLException {
        return this.convert.toBeanList(rs, type);
    }

    /**
     * Convert a <code>ResultSet</code> row into a <code>Map</code>. This
     * implementation returns a <code>Map</code> with case insensitive column
     * names as keys. Calls to <code>map.get("COL")</code> and
     * <code>map.get("col")</code> return the same value.
     *
     * @see org.apache.commons.dbutils.RowProcessor#toMap(java.sql.ResultSet)
     * @param rs
     *            ResultSet that supplies the map data
     * @throws SQLException
     *             if a database access error occurs
     * @return the newly created Map
     */
    public Map<String, Object> toMap(ResultSet rs) throws SQLException {
        Map<String, Object> result = new CaseInsensitiveHashMap();
        ResultSetMetaData rsmd = rs.getMetaData();
        int cols = rsmd.getColumnCount();

        for (int i = 1; i <= cols; i++) {
            result.put(rsmd.getColumnName(i), rs.getObject(i));
        }

        return result;
    }

    /**
     * A Map that converts all keys to lowercase Strings for case insensitive
     * lookups. This is needed for the toMap() implementation because databases
     * don't consistently handle the casing of column names.
     *
     * <p>
     * The keys are stored as they are given [BUG #DBUTILS-34], so we maintain
     * an internal mapping from lowercase keys to the real keys in order to
     * achieve the case insensitive lookup.
     *
     * <p>
     * Note: This implementation does not allow <tt>null</tt> for key, whereas
     * {@link HashMap} does, because of the code:
     *
     * <pre>
     * key.toString().toLowerCase()
     * </pre>
     */
    private static class CaseInsensitiveHashMap extends HashMap<String, Object> {
        /**
         * The internal mapping from lowercase keys to the real keys.
         *
         * <p>
         * Any query operation using the key ({@link #get(Object)},
         * {@link #containsKey(Object)}) is done in three steps:
         * <ul>
         * <li>convert the parameter key to lower case</li>
         * <li>get the actual key that corresponds to the lower case key</li>
         * <li>query the map with the actual key</li>
         * </ul>
         * </p>
         */
        private final Map<String, String> lowerCaseMap = new HashMap<String, String>();

        /**
         * Required for serialization support.
         *
         * @see java.io.Serializable
         */
        private static final long serialVersionUID = -2848100435296897392L;

        /** {@inheritDoc} */
        @Override
        public boolean containsKey(Object key) {
            Object realKey = lowerCaseMap.get(key.toString().toLowerCase(
                    Locale.ENGLISH));
            return super.containsKey(realKey);
            // Possible optimisation here:
            // Since the lowerCaseMap contains a mapping for all the keys,
            // we could just do this:
            // return lowerCaseMap.containsKey(key.toString().toLowerCase());
        }

        /** {@inheritDoc} */
        @Override
        public Object get(Object key) {
            Object realKey = lowerCaseMap.get(key.toString().toLowerCase(
                    Locale.ENGLISH));
            return super.get(realKey);
        }

        /** {@inheritDoc} */
        @Override
        public Object put(String key, Object value) {
            /*
             * In order to keep the map and lowerCaseMap synchronized, we have
             * to remove the old mapping before putting the new one. Indeed,
             * oldKey and key are not necessaliry equals. (That's why we call
             * super.remove(oldKey) and not just super.put(key, value))
             */
            Object oldKey = lowerCaseMap.put(key.toLowerCase(Locale.ENGLISH),
                    key);
            Object oldValue = super.remove(oldKey);
            super.put(key, value);
            return oldValue;
        }

        /** {@inheritDoc} */
        @Override
        public void putAll(Map<? extends String, ?> m) {
            for (Map.Entry<? extends String, ?> entry : m.entrySet()) {
                String key = entry.getKey();
                Object value = entry.getValue();
                this.put(key, value);
            }
        }

        /** {@inheritDoc} */
        @Override
        public Object remove(Object key) {
            Object realKey = lowerCaseMap.remove(key.toString().toLowerCase(
                    Locale.ENGLISH));
            return super.remove(realKey);
        }
    }

}

　　

3. [代码]BeanProcessor，也是DBUtils中的源生类，增加了一个方法

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.uncle5.pubrub.dal;

import java.beans.BeanInfo;
import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.SQLXML;
import java.sql.Timestamp;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.springframework.util.StringUtils;

/**
 * <p>
 * <code>BeanProcessor</code> matches column names to bean property names
 * and converts <code>ResultSet</code> columns into objects for those bean
 * properties.  Subclasses should override the methods in the processing chain
 * to customize behavior.
 * </p>
 *
 * <p>
 * This class is thread-safe.
 * </p>
 *
 * @see BasicRowProcessor
 *
 * @since DbUtils 1.1
 */
public class BeanProcessor {

    /**
     * Special array value used by <code>mapColumnsToProperties</code> that
     * indicates there is no bean property that matches a column from a
     * <code>ResultSet</code>.
     */
    protected static final int PROPERTY_NOT_FOUND = -1;

    /**
     * Set a bean's primitive properties to these defaults when SQL NULL
     * is returned.  These are the same as the defaults that ResultSet get*
     * methods return in the event of a NULL column.
     */
    private static final Map<Class<?>, Object> primitiveDefaults = new HashMap<Class<?>, Object>();

    /**
     * ResultSet column to bean property name overrides.
     */
    private final Map<String, String> columnToPropertyOverrides;

    static {
        primitiveDefaults.put(Integer.TYPE, Integer.valueOf(0));
        primitiveDefaults.put(Short.TYPE, Short.valueOf((short) 0));
        primitiveDefaults.put(Byte.TYPE, Byte.valueOf((byte) 0));
        primitiveDefaults.put(Float.TYPE, Float.valueOf(0f));
        primitiveDefaults.put(Double.TYPE, Double.valueOf(0d));
        primitiveDefaults.put(Long.TYPE, Long.valueOf(0L));
        primitiveDefaults.put(Boolean.TYPE, Boolean.FALSE);
        primitiveDefaults.put(Character.TYPE, Character.valueOf((char) 0));
    }

    /**
     * Constructor for BeanProcessor.
     */
    public BeanProcessor() {
        this(new HashMap<String, String>());
    }

    /**
     * Constructor for BeanProcessor configured with column to property name overrides.
     *
     * @param columnToPropertyOverrides ResultSet column to bean property name overrides
     * @since 1.5
     */
    public BeanProcessor(Map<String, String> columnToPropertyOverrides) {
        super();
        if (columnToPropertyOverrides == null) {
            throw new IllegalArgumentException("columnToPropertyOverrides map cannot be null");
        }
        this.columnToPropertyOverrides = columnToPropertyOverrides;
    }

    /**
     * Convert a <code>ResultSet</code> row into a JavaBean.  This
     * implementation uses reflection and <code>BeanInfo</code> classes to
     * match column names to bean property names.  Properties are matched to
     * columns based on several factors:
     * <br/>
     * <ol>
     *     <li>
     *     The class has a writable property with the same name as a column.
     *     The name comparison is case insensitive.
     *     </li>
     *
     *     <li>
     *     The column type can be converted to the property's set method
     *     parameter type with a ResultSet.get* method.  If the conversion fails
     *     (ie. the property was an int and the column was a Timestamp) an
     *     SQLException is thrown.
     *     </li>
     * </ol>
     *
     * <p>
     * Primitive bean properties are set to their defaults when SQL NULL is
     * returned from the <code>ResultSet</code>.  Numeric fields are set to 0
     * and booleans are set to false.  Object bean properties are set to
     * <code>null</code> when SQL NULL is returned.  This is the same behavior
     * as the <code>ResultSet</code> get* methods.
     * </p>
     * @param <T> The type of bean to create
     * @param rs ResultSet that supplies the bean data
     * @param type Class from which to create the bean instance
     * @throws SQLException if a database access error occurs
     * @return the newly created bean
     */
    public <T> T toBean(ResultSet rs, Class<T> type) throws SQLException {

        PropertyDescriptor[] props = this.propertyDescriptors(type);

        ResultSetMetaData rsmd = rs.getMetaData();

        //这里增加了对自定义annotation的支持
        createColumnToPropertyOverridesByAnnotation(type);
        int[] columnToProperty = this.mapColumnsToProperties(rsmd, props, type);

        return this.createBean(rs, type, props, columnToProperty);
    }

    /**
     * Convert a <code>ResultSet</code> into a <code>List</code> of JavaBeans.
     * This implementation uses reflection and <code>BeanInfo</code> classes to
     * match column names to bean property names. Properties are matched to
     * columns based on several factors:
     * <br/>
     * <ol>
     *     <li>
     *     The class has a writable property with the same name as a column.
     *     The name comparison is case insensitive.
     *     </li>
     *
     *     <li>
     *     The column type can be converted to the property's set method
     *     parameter type with a ResultSet.get* method.  If the conversion fails
     *     (ie. the property was an int and the column was a Timestamp) an
     *     SQLException is thrown.
     *     </li>
     * </ol>
     *
     * <p>
     * Primitive bean properties are set to their defaults when SQL NULL is
     * returned from the <code>ResultSet</code>.  Numeric fields are set to 0
     * and booleans are set to false.  Object bean properties are set to
     * <code>null</code> when SQL NULL is returned.  This is the same behavior
     * as the <code>ResultSet</code> get* methods.
     * </p>
     * @param <T> The type of bean to create
     * @param rs ResultSet that supplies the bean data
     * @param type Class from which to create the bean instance
     * @throws SQLException if a database access error occurs
     * @return the newly created List of beans
     */
    public <T> List<T> toBeanList(ResultSet rs, Class<T> type) throws SQLException {
        List<T> results = new ArrayList<T>();

        if (!rs.next()) {
            return results;
        }

        PropertyDescriptor[] props = this.propertyDescriptors(type);
        ResultSetMetaData rsmd = rs.getMetaData();
        int[] columnToProperty = this.mapColumnsToProperties(rsmd, props, type);

        do {
            results.add(this.createBean(rs, type, props, columnToProperty));
        } while (rs.next());

        return results;
    }

    /**
     * Creates a new object and initializes its fields from the ResultSet.
     * @param <T> The type of bean to create
     * @param rs The result set.
     * @param type The bean type (the return type of the object).
     * @param props The property descriptors.
     * @param columnToProperty The column indices in the result set.
     * @return An initialized object.
     * @throws SQLException if a database error occurs.
     */
    private <T> T createBean(ResultSet rs, Class<T> type,
            PropertyDescriptor[] props, int[] columnToProperty)
            throws SQLException {

        T bean = this.newInstance(type);

        for (int i = 1; i < columnToProperty.length; i++) {

            if (columnToProperty[i] == PROPERTY_NOT_FOUND) {
                continue;
            }

            PropertyDescriptor prop = props[columnToProperty[i]];
            Class<?> propType = prop.getPropertyType();

            Object value = this.processColumn(rs, i, propType);

            if (propType != null && value == null && propType.isPrimitive()) {
                value = primitiveDefaults.get(propType);
            }

            this.callSetter(bean, prop, value);
        }

        return bean;
    }

    /**
     * Calls the setter method on the target object for the given property.
     * If no setter method exists for the property, this method does nothing.
     * @param target The object to set the property on.
     * @param prop The property to set.
     * @param value The value to pass into the setter.
     * @throws SQLException if an error occurs setting the property.
     */
    private void callSetter(Object target, PropertyDescriptor prop, Object value)
            throws SQLException {

        Method setter = prop.getWriteMethod();

        if (setter == null) {
            return;
        }

        Class<?>[] params = setter.getParameterTypes();
        try {
            // convert types for some popular ones
            if (value instanceof java.util.Date) {
                final String targetType = params[0].getName();
                if ("java.sql.Date".equals(targetType)) {
                    value = new java.sql.Date(((java.util.Date) value).getTime());
                } else
                if ("java.sql.Time".equals(targetType)) {
                    value = new java.sql.Time(((java.util.Date) value).getTime());
                } else
                if ("java.sql.Timestamp".equals(targetType)) {
                    value = new java.sql.Timestamp(((java.util.Date) value).getTime());
                }
            }

            // Don't call setter if the value object isn't the right type
            if (this.isCompatibleType(value, params[0])) {
                setter.invoke(target, new Object[]{value});
            } else {
              throw new SQLException(
                  "Cannot set " + prop.getName() + ": incompatible types, cannot convert "
                  + value.getClass().getName() + " to " + params[0].getName());
                  // value cannot be null here because isCompatibleType allows null
            }

        } catch (IllegalArgumentException e) {
            throw new SQLException(
                "Cannot set " + prop.getName() + ": " + e.getMessage());

        } catch (IllegalAccessException e) {
            throw new SQLException(
                "Cannot set " + prop.getName() + ": " + e.getMessage());

        } catch (InvocationTargetException e) {
            throw new SQLException(
                "Cannot set " + prop.getName() + ": " + e.getMessage());
        }
    }

    /**
     * ResultSet.getObject() returns an Integer object for an INT column.  The
     * setter method for the property might take an Integer or a primitive int.
     * This method returns true if the value can be successfully passed into
     * the setter method.  Remember, Method.invoke() handles the unwrapping
     * of Integer into an int.
     *
     * @param value The value to be passed into the setter method.
     * @param type The setter's parameter type (non-null)
     * @return boolean True if the value is compatible (null => true)
     */
    private boolean isCompatibleType(Object value, Class<?> type) {
        // Do object check first, then primitives
        if (value == null || type.isInstance(value)) {
            return true;

        } else if (type.equals(Integer.TYPE) && Integer.class.isInstance(value)) {
            return true;

        } else if (type.equals(Long.TYPE) && Long.class.isInstance(value)) {
            return true;

        } else if (type.equals(Double.TYPE) && Double.class.isInstance(value)) {
            return true;

        } else if (type.equals(Float.TYPE) && Float.class.isInstance(value)) {
            return true;

        } else if (type.equals(Short.TYPE) && Short.class.isInstance(value)) {
            return true;

        } else if (type.equals(Byte.TYPE) && Byte.class.isInstance(value)) {
            return true;

        } else if (type.equals(Character.TYPE) && Character.class.isInstance(value)) {
            return true;

        } else if (type.equals(Boolean.TYPE) && Boolean.class.isInstance(value)) {
            return true;

        }
        return false;

    }

    /**
     * Factory method that returns a new instance of the given Class.  This
     * is called at the start of the bean creation process and may be
     * overridden to provide custom behavior like returning a cached bean
     * instance.
     * @param <T> The type of object to create
     * @param c The Class to create an object from.
     * @return A newly created object of the Class.
     * @throws SQLException if creation failed.
     */
    protected <T> T newInstance(Class<T> c) throws SQLException {
        try {
            return c.newInstance();

        } catch (InstantiationException e) {
            throw new SQLException(
                "Cannot create " + c.getName() + ": " + e.getMessage());

        } catch (IllegalAccessException e) {
            throw new SQLException(
                "Cannot create " + c.getName() + ": " + e.getMessage());
        }
    }

    /**
     * Returns a PropertyDescriptor[] for the given Class.
     *
     * @param c The Class to retrieve PropertyDescriptors for.
     * @return A PropertyDescriptor[] describing the Class.
     * @throws SQLException if introspection failed.
     */
    private PropertyDescriptor[] propertyDescriptors(Class<?> c)
        throws SQLException {
        // Introspector caches BeanInfo classes for better performance
        BeanInfo beanInfo = null;
        try {
            beanInfo = Introspector.getBeanInfo(c);

        } catch (IntrospectionException e) {
            throw new SQLException(
                "Bean introspection failed: " + e.getMessage());
        }

        return beanInfo.getPropertyDescriptors();
    }

    /**
     * The positions in the returned array represent column numbers.  The
     * values stored at each position represent the index in the
     * <code>PropertyDescriptor[]</code> for the bean property that matches
     * the column name.  If no bean property was found for a column, the
     * position is set to <code>PROPERTY_NOT_FOUND</code>.
     *
     * @param rsmd The <code>ResultSetMetaData</code> containing column
     * information.
     *
     * @param props The bean property descriptors.
     *
     * @throws SQLException if a database access error occurs
     *
     * @return An int[] with column index to property index mappings.  The 0th
     * element is meaningless because JDBC column indexing starts at 1.
     */
    protected int[] mapColumnsToProperties(ResultSetMetaData rsmd,
            PropertyDescriptor[] props, Class<?> type) throws SQLException {

        int cols = rsmd.getColumnCount();
        int[] columnToProperty = new int[cols + 1];
        Arrays.fill(columnToProperty, PROPERTY_NOT_FOUND);

        for (int col = 1; col <= cols; col++) {
            String columnName = rsmd.getColumnLabel(col);
            if (null == columnName || 0 == columnName.length()) {
              columnName = rsmd.getColumnName(col);
            }
            String propertyName = columnToPropertyOverrides.get(columnName);
            if (propertyName == null) {
                propertyName = columnName;
            }
            for (int i = 0; i < props.length; i++) {

                if (propertyName.equalsIgnoreCase(props[i].getName())) {
                    columnToProperty[col] = i;
                    break;
                }
            }
        }

        return columnToProperty;
    }

    /**
     * Convert a <code>ResultSet</code> column into an object.  Simple
     * implementations could just call <code>rs.getObject(index)</code> while
     * more complex implementations could perform type manipulation to match
     * the column's type to the bean property type.
     *
     * <p>
     * This implementation calls the appropriate <code>ResultSet</code> getter
     * method for the given property type to perform the type conversion.  If
     * the property type doesn't match one of the supported
     * <code>ResultSet</code> types, <code>getObject</code> is called.
     * </p>
     *
     * @param rs The <code>ResultSet</code> currently being processed.  It is
     * positioned on a valid row before being passed into this method.
     *
     * @param index The current column index being processed.
     *
     * @param propType The bean property type that this column needs to be
     * converted into.
     *
     * @throws SQLException if a database access error occurs
     *
     * @return The object from the <code>ResultSet</code> at the given column
     * index after optional type processing or <code>null</code> if the column
     * value was SQL NULL.
     */
    protected Object processColumn(ResultSet rs, int index, Class<?> propType)
        throws SQLException {

        if ( !propType.isPrimitive() && rs.getObject(index) == null ) {
            return null;
        }

        if (propType.equals(String.class)) {
            return rs.getString(index);

        } else if (
            propType.equals(Integer.TYPE) || propType.equals(Integer.class)) {
            return Integer.valueOf(rs.getInt(index));

        } else if (
            propType.equals(Boolean.TYPE) || propType.equals(Boolean.class)) {
            return Boolean.valueOf(rs.getBoolean(index));

        } else if (propType.equals(Long.TYPE) || propType.equals(Long.class)) {
            return Long.valueOf(rs.getLong(index));

        } else if (
            propType.equals(Double.TYPE) || propType.equals(Double.class)) {
            return Double.valueOf(rs.getDouble(index));

        } else if (
            propType.equals(Float.TYPE) || propType.equals(Float.class)) {
            return Float.valueOf(rs.getFloat(index));

        } else if (
            propType.equals(Short.TYPE) || propType.equals(Short.class)) {
            return Short.valueOf(rs.getShort(index));

        } else if (propType.equals(Byte.TYPE) || propType.equals(Byte.class)) {
            return Byte.valueOf(rs.getByte(index));

        } else if (propType.equals(Timestamp.class)) {
            return rs.getTimestamp(index);

        } else if (propType.equals(SQLXML.class)) {
            return rs.getSQLXML(index);

        } else {
            return rs.getObject(index);
        }

    }

    /**
     * 利用columnToPropertyOverrides对annotation支持
     *
     * @param type
     */
    private <T> void createColumnToPropertyOverridesByAnnotation(Class<T> type) {
        columnToPropertyOverrides.clear();
        Field[] fields = type.getDeclaredFields();
        for(Field field : fields) {
            if(field.isAnnotationPresent(ColAlias.class)) {
                ColAlias colAlias = field.getAnnotation(ColAlias.class);
                if(!StringUtils.isEmpty(colAlias.value())) {
                    columnToPropertyOverrides.put(colAlias.value(), field.getName());
                }
            }
        }
    }
}

　　

4. [代码]ColAlias， 自定义的annotation，增加别名

package com.uncle5.pubrub.dal;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface ColAlias {

    public String value() default "";
}

　　

5. [代码]javaBean实体，@ColAlias标记的是数据库字段名

public static class ForumReply {
        private Long id;
        @ColAlias("user_id")
        private Long userId;
        @ColAlias("topic_id")
        private Long topicId;
        private String title;
        private String content;
        private int floor;
        @ColAlias("create_date")
        private Date createDate;
        private Date updateDate;

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
            this.id = id;
        }

        public Long getUserId() {
            return userId;
        }

        public void setUserId(Long userId) {
            this.userId = userId;
        }

        public Long getTopicId() {
            return topicId;
        }

        public void setTopicId(Long topicId) {
            this.topicId = topicId;
        }

        public String getTitle() {
            return title;
        }

        public void setTitle(String title) {
            this.title = title;
        }

        public String getContent() {
            return content;
        }

        public void setContent(String content) {
            this.content = content;
        }

        public int getFloor() {
            return floor;
        }

        public void setFloor(int floor) {
            this.floor = floor;
        }

        public Date getCreateDate() {
            return createDate;
        }

        public void setCreateDate(Date createDate) {
            this.createDate = createDate;
        }

        public Date getUpdateDate() {
            return updateDate;
        }

        public void setUpdateDate(Date updateDate) {
            this.updateDate = updateDate;
        }

    }

　　

6. [代码]ForumReplyDaoImpl 调用例子

package com.uncle5.pubrub.dal.forum;

import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.RowMapper;
import org.springframework.jdbc.core.namedparam.BeanPropertySqlParameterSource;
import org.springframework.jdbc.core.namedparam.NamedParameterJdbcTemplate;
import org.springframework.jdbc.core.namedparam.SqlParameterSource;
import org.springframework.stereotype.Repository;

import com.uncle5.pubrub.dal.BaseDao;
import com.uncle5.pubrub.dal.MyJdbcTemplate;
import com.uncle5.pubrub.dal.model.Forum.ForumReply;

@Repository
public class ForumReplyDaoImpl implements ForumReplyDao {

    @Autowired
    protected MyJdbcTemplate myjdbc;

    protected NamedParameterJdbcTemplate getNamedJdbcTemplate() {
        return new NamedParameterJdbcTemplate(myjdbc);
    }

    @Override
    public void saveForumReply(ForumReply forumReply) {
        int nextFloor = getNextSequence("floor");
        forumReply.setFloor(nextFloor);

        String sql = "insert into forum_reply(user_id, topic_id, title, content, floor, create_date) "
                + "values(:userId, :topicId, :title, :content, :floor, now())";
        SqlParameterSource forumReplyParams = new BeanPropertySqlParameterSource(
                forumReply);
        getNamedJdbcTemplate().update(sql, forumReplyParams);
    }

    @Override
    public List<ForumReply> queryForumReplysByTopicId(Long topicId) {
        String sql = "select * from forum_reply where topic_id = ?";

        // 原生写法
        List<ForumReply> forumReplies = myjdbc.query(sql,
                new Object[] { topicId }, new RowMapper<ForumReply>() {

                    @Override
                    public ForumReply mapRow(ResultSet rs, int rowNum)
                            throws SQLException {
                        ForumReply forumReply = new ForumReply();
                        forumReply.setId(rs.getLong("id"));
                        forumReply.setTopicId(rs.getLong("topic_id"));
                        forumReply.setUserId(rs.getLong("user_id"));
                        forumReply.setTitle(rs.getString("title"));
                        forumReply.setContent(rs.getString("content"));
                        forumReply.setFloor(rs.getInt("floor"));
                        forumReply.setCreateDate(rs.getDate("create_date"));
                        forumReply.setUpdateDate(rs.getDate("update_date"));

                        return forumReply;
                    }
                });

        // 调用queryForBeanList方法
        forumReplies = myjdbc.queryForBeanList(sql, ForumReply.class, topicId);

        return forumReplies;
    }
}

　　

7. [代码]原理说明

1.调用queryForBean(List)方法时候，其实只是利用原生的

public <T> T query(String sql, Object[] args, ResultSetExtractor<T> rse) throws DataAccessException；

方法，当得到ResultSet对象时候，调用BasicRowProcessor的

public <T> T toBean(ResultSet rs, Class<T> type) throws SQLException；

方法，进而调用BeanProcessor中的，

public <T> T toBean(ResultSet rs, Class<T> type) throws SQLException；

方法，（其实BasicRowProcessor这步可以省略掉，我这里没有省略，）主要可以看下

protected int[] mapColumnsToProperties(ResultSetMetaData rsmd,
            PropertyDescriptor[] props, Class<?> type) throws SQLException；

这个方法，其实就是将javaBean中的属性与ResultSet中columnName进行比较，如果一样，就会在接下来赋值时候

调用对应rs.getXXX(int index)方法进行赋值。在这里，原生的DBUtils中的这个类已经支持了自定义别名的一个

map--columnToPropertyOverrides，来对属性名称进行改写以供和ResultSet中的ColumnName进行匹配比

较，我增加的也不过是根据annotation构造一个columnToPropertyOverrides，来完成这个操作。

另外还有一个做法：如果sql都是自己维护的话，其实可以采用类似 

select user_id as userId from table_user where ...

的方式，这样就可以采用原本的jdbcTemplate操作了，写的比较乱，大家随便看看，能用就行哈。

上面的利用DButils的类自动转换的功能，我也已经尝试过了，确实可以实现自动转换，但是不知道有没有什么bug。

看了原作者的评论，但是不太明白bug指的哪里，怎么修复，说：

昨天发现了一个bug，就是在BeanProcessor类中的toBean方法里，之前我考虑的是如果columnToPropertyOverrides为空就进行annotation支持，但是因为MyJdbcTemplate这个类被spring托管，默认为单例，也就是实际上只有一个实例化出来的BeanProcessor，这样就会出现当第一次执行createColumnToPropertyOverridesByAnnotation之后，就不会再次执行这个方法了，已经修改了，也请你这边注意下。