1.DaoImpl有如下代码,查询结果显示ClientMonitorRecordEntity
中b2cUserCode和createDateTime值为null
List<ClientMonitorRecordEntity> list = dalClient.queryForList("logClientMonitor.query_client_monitor_record_by_conditions",
param, ClientMonitorRecordEntity.class);ClientMonitorRecordEntity类结构如下
/**
* 主键
*/
private Integer id;
/**
* 易购号
*/
private String b2cUserCode;
/**
* 创建时间。格式：YYYY-MM-DD HH:mm:ss
*/
private String createDateTime;
@Column(name = "b2c_user_code")
public String getB2cUserCode() {
return b2cUserCode;
}
@Column(name = "create_datetime")
public String getCreateDateTime() {
return createDateTime;
}
.....二. 定位
org.springframework.jdbc.core.JdbcTemplate
public <T> T query(
PreparedStatementCreator psc, final PreparedStatementSetter pss, final ResultSetExtractor<T> rse)
throws DataAccessException {
Assert.notNull(rse, "ResultSetExtractor must not be null");
logger.debug("Executing prepared SQL query");
return execute(psc, new PreparedStatementCallback<T>() {
public T doInPreparedStatement(PreparedStatement ps) throws SQLException {
ResultSet rs = null;
try {
if (pss != null) {
pss.setValues(ps);
}
rs = ps.executeQuery();
ResultSet rsToUse = rs;
if (nativeJdbcExtractor != null) {
rsToUse = nativeJdbcExtractor.getNativeResultSet(rs);
}
//主要关注这里结果集处理
return rse.extractData(rsToUse);
}
finally {
JdbcUtils.closeResultSet(rs);
if (pss instanceof ParameterDisposer) {
((ParameterDisposer) pss).cleanupParameters();
}
}
}
});
}org.springframework.jdbc.core.RowMapperResultSetExtractor
public List<T> extractData(ResultSet rs) throws SQLException {
List<T> results = (this.rowsExpected > 0 ? new ArrayList<T>(this.rowsExpected) : new ArrayList<T>());
int rowNum = 0;
while (rs.next()) {
//子类BeanPropertyRowMapper处理映射
results.add(this.rowMapper.mapRow(rs, rowNum++));
}
return results;
}org.springframework.jdbc.core.BeanPropertyRowMapper
public T mapRow(ResultSet rs, int rowNumber) throws SQLException {
Assert.state(this.mappedClass != null, "Mapped class was not specified");
T mappedObject = BeanUtils.instantiate(this.mappedClass);
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(mappedObject);
initBeanWrapper(bw);
ResultSetMetaData rsmd = rs.getMetaData();
int columnCount = rsmd.getColumnCount();
Set<String> populatedProperties = (isCheckFullyPopulated() ? new HashSet<String>() : null);
for (int index = 1; index <= columnCount; index++) {
//读取数据库字段
String column = JdbcUtils.lookupColumnName(rsmd, index);
//从mappedFields中根据数据库字段获取对应的类字段信息，可以发现循环到b2cUserCode和createDateTime时pd都是null
//跟踪mappedFields发现是初始化时赋值的，参见步骤4
PropertyDescriptor pd = this.mappedFields.get(column.replaceAll(" ", "").toLowerCase());
if (pd != null) {
try {
Object value = getColumnValue(rs, index, pd);
if (logger.isDebugEnabled() && rowNumber == 0) {
logger.debug("Mapping column '" + column + "' to property '" +
pd.getName() + "' of type " + pd.getPropertyType());
}
try {
bw.setPropertyValue(pd.getName(), value);
}
catch (TypeMismatchException e) {
if (value == null && primitivesDefaultedForNullValue) {
logger.debug("Intercepted TypeMismatchException for row " + rowNumber +
" and column '" + column + "' with value " + value +
" when setting property '" + pd.getName() + "' of type " + pd.getPropertyType() +
" on object: " + mappedObject);
}
else {
throw e;
}
}
if (populatedProperties != null) {
populatedProperties.add(pd.getName());
}
}
catch (NotWritablePropertyException ex) {
throw new DataRetrievalFailureException(
"Unable to map column " + column + " to property " + pd.getName(), ex);
}
}
}
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;
}- mappedFields初始化
protected void initialize(Class<T> mappedClass) {
this.mappedClass = mappedClass;
this.mappedFields = new HashMap<String, PropertyDescriptor>();
this.mappedProperties = new HashSet<String>();
//反射类中所有字段
PropertyDescriptor[] pds = BeanUtils.getPropertyDescriptors(mappedClass);
for (PropertyDescriptor pd : pds) {
if (pd.getWriteMethod() != null) {
//mappedFields中添加 小写原始字段字符串,注意这一步，涉及到后续解决方法
this.mappedFields.put(pd.getName().toLowerCase(), pd);
//根据字段名称处理，如果处理后的字段值不等于字段名称，则添加处理后的值
String underscoredName = underscoreName(pd.getName());
if (!pd.getName().toLowerCase().equals(underscoredName)) {
this.mappedFields.put(underscoredName, pd);
}
this.mappedProperties.add(pd.getName());
}
}
}
private String underscoreName(String name) {
StringBuilder result = new StringBuilder();
if (name != null && name.length() > 0) {
//1.将第一个字符转成小写
result.append(name.substring(0, 1).toLowerCase());
//2.从第二个字符开始遍历
for (int i = 1; i < name.length(); i++) {
String s = name.substring(i, i + 1);
//3.如果字符 = 该字符的大写，注意此处如果是数字则会判断为true
if (s.equals(s.toUpperCase())) {
//4.添加“_”,并将大写转换为小写
result.append("_");
result.append(s.toLowerCase());
}
else {
result.append(s);
}
}
}
return result.toString();
}underscoreName解释了问题的原因：因为数据库字段默认都是“hello_world”这种命名，underscoreName本意是将所有大写字符转换成"_"+小写字符。
但是形如b2cUserCode这种带数字的字符，在判断是否大写的时候，会导致误判，导致转换成b_2c_user_code,
而createDateTime则转换成create_date_time和数据库字段create_datetime不一致。
我认为datetime是一个单词，所以数据库命名时没有采用create_date_time
- 通过重新命名符合spring规则的字段
- 修改sql，添加别名 如select b_2c_user_code as b2cUserCode 之所以这样可以生效，是因为上述代码中有这样一段
this.mappedFields.put(pd.getName().toLowerCase(), pd);所以b2cUserCode在mappedFields中可以找到。
underscoreName这种转换方式太固定，肯定会遇到不一致的情况。原以为spring会解析字段上的注解采用注解上的name来映射，但实际却不是这样。具体原因是什么呢？