1，NamedParameterJdbcTemplate 查询列表
/***测试***/
public void queyBeanTest(){
String s = "select * from PT_USER ";
List<PtUser> list = namedJdbcTemplate.query(s, new BeanPropertyRowMapper<PtUser>(PtUser.class));
System.out.println(list);
}
2，如果有参数，期间会把 参数绑定的 例如： :name 替换成 ?
源码：getPreparedStatementCreator 方法。 所以最后还是调用 JdbcTemplate 模板。
3，按源码一直走下去。下面是一个抽象类实现的模板方法。
/**
* Query using a prepared statement, allowing for a PreparedStatementCreator
* and a PreparedStatementSetter. Most other query methods use this method,
* but application code will always work with either a creator or a setter.
* @param psc Callback handler that can create a PreparedStatement given a
* Connection
* @param pss object that knows how to set values on the prepared statement.
* If this is null, the SQL will be assumed to contain no bind parameters.
* @param rse object that will extract results.
* @return an arbitrary result object, as returned by the ResultSetExtractor
* @throws DataAccessException if there is any problem
*/
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>() {
@Override
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);
}
return rse.extractData(rsToUse);
}
finally {
JdbcUtils.closeResultSet(rs);
if (pss instanceof ParameterDisposer) {
((ParameterDisposer) pss).cleanupParameters();
}
}
}
});
}
4，因为一开始 我们 用的 BeanPropertyRowMapper 类，也就是用这个类来装载返回的数据。
一开始new 的时候会初始化方法。
/**
* Create a new {@code BeanPropertyRowMapper}, accepting unpopulated
* properties in the target bean.
* <p>Consider using the {@link #newInstance} factory method instead,
* which allows for specifying the mapped type once only.
* @param mappedClass the class that each row should be mapped to
*/
public BeanPropertyRowMapper(Class<T> mappedClass) {
initialize(mappedClass);
}
这个方法，其实是把实体类的属性拆分了来存的，例如：userName 存为user_name.
/**
* Initialize the mapping metadata for the given class.
* @param mappedClass the mapped class
*/
protected void initialize(Class<T> mappedClass) {
this.mappedClass = mappedClass;
this.mappedFields = new HashMap<String, PropertyDescriptor>();
this.mappedProperties = new HashSet<String>();
PropertyDescriptor[] pds = BeanUtils.getPropertyDescriptors(mappedClass);
for (PropertyDescriptor pd : pds) {
if (pd.getWriteMethod() != null) {
this.mappedFields.put(lowerCaseName(pd.getName()), pd);
String underscoredName = underscoreName(pd.getName());
if (!lowerCaseName(pd.getName()).equals(underscoredName)) {
this.mappedFields.put(underscoredName, pd);
}
this.mappedProperties.add(pd.getName());
}
}
}
下面这个方法是最终实现，会把数据库的字段都转成小写。所以也支持Oracle 。
/**
* Extract the values for all columns in the current row.
* <p>Utilizes public setters and result set metadata.
* @see java.sql.ResultSetMetaData
*/
@Override
public T mapRow(ResultSet rs, int rowNumber) throws SQLException {
Assert.state(this.mappedClass != null, "Mapped class was not specified");
T mappedObject = BeanUtils.instantiateClass(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++) {
String column = JdbcUtils.lookupColumnName(rsmd, index);
String field = lowerCaseName(column.replaceAll(" ", ""));
PropertyDescriptor pd = this.mappedFields.get(field);
if (pd != null) {
try {
Object value = getColumnValue(rs, index, pd);
if (rowNumber == 0 && logger.isDebugEnabled()) {
logger.debug("Mapping column '" + column + "' to property '" + pd.getName() +
"' of type '" + ClassUtils.getQualifiedName(pd.getPropertyType()) + "'");
}
try {
bw.setPropertyValue(pd.getName(), value);
}
catch (TypeMismatchException ex) {
if (value == null && this.primitivesDefaultedForNullValue) {
if (logger.isDebugEnabled()) {
logger.debug("Intercepted TypeMismatchException for row " + rowNumber +
" and column '" + column + "' with null value when setting property '" +
pd.getName() + "' of type '" +
ClassUtils.getQualifiedName(pd.getPropertyType()) +
"' on object: " + mappedObject, ex);
}
}
else {
throw ex;
}
}
if (populatedProperties != null) {
populatedProperties.add(pd.getName());
}
}
catch (NotWritablePropertyException ex) {
throw new DataRetrievalFailureException(
"Unable to map column '" + column + "' to property '" + pd.getName() + "'", ex);
}
}
else {
// No PropertyDescriptor found
if (rowNumber == 0 && logger.isDebugEnabled()) {
logger.debug("No property found for column '" + column + "' mapped to field '" + field + "'");
}
}
}
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.getName() + "]: " +
this.mappedProperties);
}
return mappedObject;
}
总结： 因为源码就是这样写死的。所以要约定装配实体类。
