标签：springmvc jdbctemplate springjdbc springmvc字段映射
使用SpringMVC搭建项目时，我打算直接使用SpringMVC的JDBC，如果引入Mybatis和Hibernate等ORM是感觉太过的麻烦，所以直接使用springframework.jdbc。SpringMVCJDBC提供了两个数据jdbc操作类，分别是：jdbcTemplate和namedParameterJdbcTemplate。他们都提供了非常多的方法，我就不写了（看源码）。现在问题来了，我想从数据库中返回映射到实体该如何办呢？
现在我有表user表，需返回UserInfo实体，以及List<UserInfo>时。
UserInfo实体如下：
package org.andy.shop.entity;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Date;
public class UserInfo {
private Integer id;
private String uname;
private Integer unumber;
private Date uRegisterTime;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getUname() {
return uname;
}
public void setUname(String uname) {
this.uname = uname == null ? null : uname.trim();
}
public Integer getUnumber() {
return unumber;
}
public void setUnumber(Integer unumber) {
this.unumber = unumber;
}
public Date getuRegisterTime() {
return uRegisterTime;
}
public void setuRegisterTime(Date uRegisterTime) {
this.uRegisterTime = uRegisterTime;
}
}在上面的UserInfo中添加转换的方法：
public static UserInfo toObject(Map<String, Object> map) {
UserInfo userInfo = new UserInfo();
userInfo.setId((Integer) map.get("id"));
userInfo.setUname((String) map.get("uname"));
userInfo.setUnumber((Integer) map.get("unumber"));
userInfo.setuRegisterTime((Date) map.get("uregister_time"));
return userInfo;
}
public static List<UserInfo> toObject(List<Map<String, Object>> lists){
List<UserInfo> userInfos = new ArrayList<UserInfo>();
for (Map<String, Object> map : lists) {
UserInfo userInfo = UserInfo.toObject(map);
if (userInfo != null) {
userInfos.add(userInfo);
}
}
return userInfos;
}
public Map<String, Object> queryForMap(String sql, Object... args) throws DataAccessException
public List<Map<String, Object>> queryForList(String sql) throws DataAccessException
在调用上述的转换。
@Autowired
private JdbcTemplate jdbcTemplate;
@Autowired
private NamedParameterJdbcTemplate namedParameterJdbcTemplate;
@Override
public UserInfo getById(Integer id) {
String sql = "SELECT * FROM user_info WHERE id = ?";
Map<String, Object> map = jdbcTemplate.queryForMap(sql, new Object[]{1});
return UserInfo.toObject(map);
}
@Override
public List<UserInfo> findAll() {
String sql = "SELECT * FROM user_info";
List<Map<String, Object>> lists = jdbcTemplate.queryForList(sql);
return UserInfo.toObject(lists);
}
查看Spring JDBC的源码，我们会发先，还提供了如下的方法：
public <T> T queryForObject(String sql, RowMapper<T> rowMapper, Object... args) throws DataAccessException
public <T> List<T> query(String sql, RowMapper<T> rowMapper) throws DataAccessException
这里面需要传过去一个返回实体的实现RowMapper的Mapper类。好吧，我们改造UserInfo，实现RowMapper接口，实现接口里的mapRow方法。
UserInfo实体修改如下：
package org.andy.shop.entity;
import java.io.Serializable;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Date;
import org.springframework.jdbc.core.RowMapper;
/**
* 实现数据表与字段的映射
*
* @author andy
*
*/
public class UserInfo implements RowMapper<UserInfo>, Serializable {
/**
*
*/
private static final long serialVersionUID = -8823504831198719837L;
private Integer id;
private String uname;
private Integer unumber;
private Date uRegisterTime;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getUname() {
return uname;
}
public void setUname(String uname) {
this.uname = uname == null ? null : uname.trim();
}
public Integer getUnumber() {
return unumber;
}
public void setUnumber(Integer unumber) {
this.unumber = unumber;
}
public Date getuRegisterTime() {
return uRegisterTime;
}
public void setuRegisterTime(Date uRegisterTime) {
this.uRegisterTime = uRegisterTime;
}
@Override
public UserInfo mapRow(ResultSet rs, int rowNum) throws SQLException {
UserInfo userInfo = new UserInfo();
userInfo.setId(rs.getInt("id"));
userInfo.setUname(rs.getString("uname"));
userInfo.setUnumber(rs.getInt("unumber"));
userInfo.setuRegisterTime(rs.getDate("uregister_time"));
return userInfo;
}
}
@Autowired
private JdbcTemplate jdbcTemplate;
@Autowired
private NamedParameterJdbcTemplate namedParameterJdbcTemplate;
@Override
public UserInfo getById(Integer id) {
String sql = "SELECT * FROM user_info WHERE id = ?";
UserInfo userInfo = jdbcTemplate.queryForObject(sql, new UserInfo(),
new Object[] { id });
return userInfo;
}
@Override
public List<UserInfo> findAll() {
String sql = "SELECT * FROM user_info";
List<UserInfo> userInfos = jdbcTemplate.query(sql, new UserInfo());
return userInfos;
} 但是我们查看JDBC源码时，我们还看到了如下的方法
public <T> T queryForObject(String sql, Class<T> requiredType, Object... args) throws DataAccessException
public <T> List<T> queryForList(String sql, Class<T> elementType) throws DataAccessException
那我们能否分别如下的调用呢？
UserInfo userInfo = jdbcTemplate.queryForObject(sql, UserInfo.class,
new Object[] { id });
List<UserInfo> userInfos = jdbcTemplate.queryForList(sql, UserInfo.class);
执行JUnit测试，结果如下：
org.springframework.jdbc.IncorrectResultSetColumnCountException: Incorrect column count: expected 1, actual 4
at org.springframework.jdbc.core.SingleColumnRowMapper.mapRow(SingleColumnRowMapper.java:88)
at org.springframework.jdbc.core.RowMapperResultSetExtractor.extractData(RowMapperResultSetExtractor.java:93)
at org.springframework.jdbc.core.RowMapperResultSetExtractor.extractData(RowMapperResultSetExtractor.java:60)
at org.springframework.jdbc.core.JdbcTemplate$1QueryStatementCallback.doInStatement(JdbcTemplate.java:460)
at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:405)
at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:471)
at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:481)
at org.springframework.jdbc.core.JdbcTemplate.queryForList(JdbcTemplate.java:516)
at org.andy.shop.dao.Impl.UserInfoDaoImpl.findAll(UserInfoDaoImpl.java:43)
at org.andy.shop.service.Impl.UserInfoServiceImpl.findAll(UserInfoServiceImpl.java:31)
at org.andy.shop.test.service.TestUserInfoService.testFindAll(TestUserInfoService.java:37)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:73)
at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:82)
at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:73)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:217)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:83)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:68)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:163)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
意思是返回结果期望是1，结果是4列。（数据库中是一行数据，四个列）
这是为什么呢？我们继续查看JDBC源码，
public <T> T queryForObject(String sql, Class<T> requiredType, Object... args) throws DataAccessException源码如下：
@Override
public <T> T queryForObject(String sql, Class<T> requiredType, Object... args) throws DataAccessException {
return queryForObject(sql, args, getSingleColumnRowMapper(requiredType));
} getSingleColumnRowMapper只是通过反射获取了UserInfo，并最终是要执行它里面的的映射方法，因为我们给UserInfo实现了RowMapper的方法。
这个最终调用了public <T> T queryForObject(String sql, RowMapper<T> rowMapper, Object... args) throws DataAccessException方法。和为什么上面的能获取这个就报错呢，看源码后可以发现：
public <T> T queryForObject(String sql, Class<T> requiredType, Object... args) throws DataAccessException 这种反射类型的是将每一个数据列返回为T类型，故出错，因此此方法只支持这种数据类型的（如String等等），不支持自己定义复杂类型的Bean实体。因此可以返回单列的（例如count(*) 和 某一列值等等）。
但是它在文档上未做任何的说明，害得我测试了半天，真是节操何在？
博客来源：http://blog.csdn.net/fengshizty?viewmode=list
SpringMVC jdbcTemplate中queryForObject以及queryForList返回映射实体使用
标签：springmvc jdbctemplate springjdbc springmvc字段映射
原文地址：http://blog.csdn.net/fengshizty/article/details/43309055
