Xml an xml go into another proxy execution, file import db.properties guide xml.
<context:property-placeholder location="classpath:conf/*.properties"/>
//导入所有配置文件
<import resource="applicationContext-dao.xml"/>
//这个导入目前仅在Spring中用过Objects are injected when the injection is an interface class
Exception mechanism is constantly throwing up until he reached the top level is considered to give up. If you have not resolved it will fryer.
throw and throws an exception is thrown, all thrown to try. This program only try to define outer layer, or the outermost layer. If you try not to deal with it would have been thrown until jvm jvm error. Adding information which could throw into customized, prompt and friendly to the front end, but it will only give throws default system error message, unfriendly.
try is to grab, throw (s) is responsible for the throw, so try to define `throw at the top, so he could guarantee can catch errors. You can define multiple layers try. You can specify which objects throw an exception to be thrown, but not necessarily wrong. But to throw to throw, throw what you want to throw anything, you can also add your own information. But that is entirely jvm throws the final say, throw it is the actual situation encountered before throwing, you can not add your own information.
The concept of this top is the order of program execution that was first performed at the top level, outside can also have a lot of layers. Since the implementation of throwing up an error is encountered.
select query has the idea of choice.
Do not use other types to String + "" This may be scolded and inefficient. It can be optimized on the future, this optimization easy.