Encapsulate the query results into List & lt; Map & gt; and Use callback functions to dynamically encapsulate data (44). map callback function

Encapsulate query results into List <Map> and Use callback functions to dynamically encapsulate data (44). map callback function

Start the QueryRunner class manually. Data encapsulation:

MapListHandler

MapHandler

BeanListHandler

BeanHandler

Step 1: Basic encapsulation Test

Write a class, QueryRunner, and implement a method query (SQL)-List <map>

package cn.itcast.dbutils;import java.sql.Connection;import java.sql.ResultSet;import java.sql.ResultSetMetaData;import java.sql.SQLException;import java.sql.Statement;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import javax.sql.DataSource;

Public class QueryRunner {// receives a ds private DataSource ds; public QueryRunner () {} public QueryRunner (DataSource ds) {this. ds = ds;}/*** is encapsulated into a List <Map> */public List <Map <String, Object> query (String SQL) {// encapsulate data using List <Map <String, Object> list = new ArrayList <Map <String, Object> (); // declare the returned Object Connection con = null; try {con = ds. getConnection (); // execute the query Statement st = con. createStatement (); ResultSet rs = st.exe cuteQuery (SQL); // analysis result set ResultSetMetaData rsmd = rs. getMetaData (); // get the number of columns int cols = rsmd. getColumnCount (); // traverses data while (rs. next () {// Map a row of Data <String, Object> mm = new HashMap <String, Object> (); // traverse the column for (int I = 0; I <cols; I ++) {// obtain the column name String colName = rsmd. getColumnName (I + 1); // get data Object val = rs. getObject (I + 1); // encapsulate it in map mm. put (colName, val);} // put this map to list. add (mm) ;}} catch (Exception e) {throw new RuntimeException (e);} finally {try {con. close ();} catch (SQLException e) {e. printStackTrace () ;}} return list ;}}

Dynamic Data encapsulation using callback Functions

A callback is implemented by a third-party class during execution.

Callback is generally composed of two parts:

1: call class-QueryRunner. Instance type

2: callback specification-ResultSetHandler. It is generally an interface.

3: The callback Specification defines the callback method and this method is called by the call class.

PackageCn. itcast. demo;

ImportJava. util. ArrayList;

ImportJava. util. List;

ImportOrg. junit. Test;

Public ClassThreadDemo {

/**

* Testing generics

*@ ThrowsException

*/

@ Test

Public VoidAa ()ThrowsException {

// Generic, with no location at runtime.

List <String> list =NewArrayList <String> ();

List. add ("ddd ");

List list2 = list;

List2.add( 777 );

List. getClass (). getMethod ("add", Object.Class). Invoke (list, 909 );

For(Object o: list ){

System.Err. Println (o + "," + o. getClass ());

}

}

/**

* Test thread

*@ ParamArgs

*/

Public Static VoidMain (String [] args ){

NewThread (

NewRunnable (){

Public VoidRun (){

System.Err. Println ("B This is runnable. run .... ");

}

}

){

Public VoidRun (){

Super. Run (); // call the method of the parent class to execute runnalble. run

System.Err. Println ("A This is thread. run ....");

};

}. Start ();

}

}