1.查询单个字段
Object queryForObject(String sql, Object[] args, Class requiredType)
其中Class requiredType 参数为返回值的类型(可以为常见的类库中的类类型)比如String.class
参数“requiredType”不可以是自定义的类
2.查询多个字段
Object queryForObject(String sql, Object[] args, RowMapper rowMapper)
其中Rowmapper 需要new一下 给该接口一个类类型,它负责给你返回一个对象(需要什么值要自己set,建议全部set)
如果要把查询结果封装为自定义的类,需要采用第2个方法
//只查询一列:name
String sql = "SELECT NAME FROM CUSTOMER WHERE CUST_ID = ?";
String name = (String)getJdbcTemplate().queryForObject(
sql, new Object[] { custId }, String.class);
return name;
//查询返回自定义的类
String sql = "SELECT * FROM CUSTOMER WHERE CUST_ID = ?";
Customer customer = (Customer)getJdbcTemplate().queryForObject(
sql, new Object[] { custId },
new BeanPropertyRowMapper(Customer.class));
return customer;
我们接着分析下BeanPropertyRowMapper
其实不用看源码都知道思路了:
new BeanPropertyRowMapper(User.class)
mapRow(ResultSet rs, int rowNumber)
遍历ResultSet,每一行对应一个User 对象
遍历每一行时,顺序遍历各列,取得该列的值通过反射调用对应的setter方法,赋值给到User 对象
注意到无论是取列名还是取列的值,都是通过index(1~columnCount)来取的
public T mapRow(ResultSet rs, int rowNumber) throws SQLException { T mappedObject = BeanUtils.instantiate(this.mappedClass); BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(mappedObject); ResultSetMetaData rsmd = rs.getMetaData(); int columnCount = rsmd.getColumnCount(); Set<String> populatedProperties = (isCheckFullyPopulated() ? new HashSet<String>() : null); for (int index = 1; index <= columnCount; index++) { String column = JdbcUtils.lookupColumnName(rsmd, index); PropertyDescriptor pd = this.mappedFields.get(column.replaceAll(" ", "").toLowerCase()); if (pd != null) { try { Object value = getColumnValue(rs, index, pd); bw.setPropertyValue(pd.getName(), value); if (populatedProperties != null) { populatedProperties.add(pd.getName()); } } } } if (populatedProperties != null && !populatedProperties.equals(this.mappedProperties)) { throw new InvalidDataAccessApiUsageException("Given ResultSet does not contain all fields " + "necessary to populate object of class [" + this.mappedClass + "]: " + this.mappedProperties); } return mappedObject; }
注意到mapRow方法里面,populatedProperties变量是用来检查是否所有的property都正确地实现了赋值
再看看BeanPropertyRowMapper的构造函数:
public BeanPropertyRowMapper(Class<T> mappedClass) {
initialize(mappedClass);
}
protected void initialize(Class<T> mappedClass) {
this.mappedClass = mappedClass;
/*保存field
注意到对于驼峰式命名的field:
例如,对于gameId, mappedFields 会同时保存"gameId"和"game_id"
因此在sql语句中,
select id as game_id, name from game和
select id as gameId, name from game的效果是一样的
*/
this.mappedFields = new HashMap<String, PropertyDescriptor>();
//保存property
this.mappedProperties = new HashSet<String>();
PropertyDescriptor[] pds = BeanUtils.getPropertyDescriptors(mappedClass);
for (PropertyDescriptor pd : pds) {
if (pd.getWriteMethod() != null) {
this.mappedFields.put(pd.getName().toLowerCase(), pd);
String underscoredName = underscoreName(pd.getName());
if (!pd.getName().toLowerCase().equals(underscoredName)) {
this.mappedFields.put(underscoredName, pd);
}
this.mappedProperties.add(pd.getName());
}
}
}
//1. "game", return "game", unchanged
//2. "gameId", return "game_id"
private String underscoreName(String name) {
//......
}
二、查询返回对象或者list
思路:首先在Bean里面实现RowMapper和序列化接口(序列化可有可无)
接着在maprow方法中将rs取出来的值set到当前Bean对象里面
当然命名也要响应的变化下比如:UserPo,然后返回该对象最
后在new 的RowMapper接口中直接new 该Po就ok
【此方法适用于查询单个对象,或者多个对象组成的List或者Map】
/** * 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; }
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三、第三种方法
使用很少人使用的RowSet
SqlRowSet set = queryForRowSet(sql,对象参数数组);
if(set==null){
new AuthenticationException("null");
}
while(set.next){
遍历:
set.getString(此处参数类型为整形,表示你想要查出来的结果,按照顺序,依次是1、2、3.......索引从1开始)
}
注意该方法适用于:查询单个对象或者List,Map结果的情况
必须谨记若用他查出来一条数据或者一个对象时:
在判断条件的时候必须加set.next&&在跟其他条件,否则会报错"光标位置失效"