Three questions JavaBean

previously thoughtJavabenanare someJavaclass.later viewa number of Wikipedia .JavaBeanis aJavaComponent Technology,and follow some conventions ..I don't understand ..

What is javabean?

in the JSP program used to encapsulate business logic , database operations and classes for entities .

How to understand the above component technology

these written Span lang= "en-US" style= "Font-family:calibri" >java Span lang= "en-US" style= "Font-family:calibri", is placed in a package of attributes , You can package these bracketing jar Format Strong reusability Compile once Feel free to run

What to follow attribute constraints?

1 by Property , Method,event composition .

2 must have Public the parameter-free constructor

3 class naming Xxxbean

In a comprehensive view , JavaBean is the class that we previously encapsulated with a parameterless constructor , This class has attribute methods, etc. .

We use examples to see

JavaBean in User class

Package Com.bjpower.drp.sysmgr.domain;import Java.util.date;public class User {public String getUserId () {return userId ;} public void Setuserid (String userId) {this.userid = userId;} Public String GetUserName () {return userName;} public void Setusername (String userName) {this.username = UserName;} Public String GetPassword () {return password;} public void SetPassword (String password) {this.password = password;} Public String Getcontacttel () {return contacttel== null? "": Contacttel;} public void Setcontacttel (String contacttel) {This.contacttel = Contacttel;} Public String Getemail () {return email = = NULL? "": email;} public void Setemail (String email) {this.email = email;} Public Date Getcreatedate () {return createdate;} public void Setcreatedate (Date createdate) {this.createdate = CreateDate;} Useridprivate string userid;//usernameprivate string username;//passwordprivate string Password;private string conta Cttel;private String email;//util dateprivate Date createdate;}

in this class , we set the member variable to Private, set the property to Public , and for getxxxx ( variable name ).

Control class

Package Com.bjpower.sysmgr;//c+f+oimport Java.sql.connection;import Java.sql.preparedstatement;import Java.sql.resultset;import Java.sql.sqlexception;import Java.sql.statement;import Java.sql.Timestamp;import Java.util.arraylist;import Java.util.date;import Java.util.list;import Com.bjpower.drp.sysmgr.domain.user;import Com.bjpower.drp.util.dbutil;import com.bjpower.drp.util.pagemodel;/** * Using a singleton mode * @author V-hanyk * */public class Usermanager {private static Usermanager instance=null;private Usermanager () {}//Portal method public static synchronized Usermanager Getusermangwer () {if (instance== null) {instance = new Usermanager ();} return instance;} @Overrideprotected void Doget (HttpServletRequest req, HttpServletResponse resp) throws Servletexception, IOException {/ /must show call parent class method if (Constants.ADD.equals (GetCommand ())) {ADD (req, resp);} else if (Constants.DEL.equals (GetCommand ())) { Delete (req, resp);} else if (Constants.MOIDFY.equals (GetCommand ())) {Modify (req, resp);} else if (Constants.SHOW_ADD.equals (GetCommand ())) {Showadd (req, resp);} else if (Constants.QUERY.equals (GetCommand ())) {//Query Finduserbyid (req, resp);}} /** * Query users according to user code * @param req* @param resq * @return * @throws SQLException */public void Finduserbyid (httpservletrequest Req, HttpServletResponse resp) throws Exception {StringBuffer sql= new StringBuffer (); Sql.append ("Select user_id, User_ Name, password, Contact_tel, email, create_date from T_user where user_id=? "); Connection Conn=null; PreparedStatement Pstmt=null; ResultSet rs= null; User User=null; String userid=req.getparameter ("UserId"), try{conn= dbutil.getconnection ();p stmt=conn.preparestatement ( Sql.tostring ());p stmt.setstring (1, userId); Rs=pstmt.executequery (); if (Rs.next ()) {user=new user (); User.setuserid ( Rs.getstring ("user_id")), User.setusername (rs.getstring ("user_name")), User.setpassword (rs.getstring ("password") ); User.setcontacttel (rs.getstring ("Contact_tel")); User.setemail (rs.getstring ("email")); User.setcreatedate ( Rs.gettimestamp ("Create_date"));} Req.setattribute ("User", user),//redirect without Resq and Resq, if forwarding with req and reqs (inside) resp.sendredirect (Req.getcontextpath () + "/servlet/flowcard/ Flowcardservlet?command=q ");} catch (SQLException e) {e.printstacktrace ();} Finally{dbutil.close (RS);D butil.close (pstmt);D butil.close (conn);} return user;}}

 

Control class is a simple business processing class, not JavaBean class in the.

View page Get JavaBean the Data

through EL An expression

<table width= "95%" border= "0" cellpadding= "0" cellspacing= "0" ><tr><td width= "22%" height= "><" Div align= "Right" > User code: </DIV></TD><TD width= "78%" ><input name= "userId" type= "text" class= " Text1 "id=" userId "size=" "Maxlength=" readonly= "true" Value=${user. ID}></TD></TR><TR><TD height= "><div" align= "right" ><font color= "#FF0000" >*</font> User name: </div></td><td><input name= "UserName" type= "text" class= "Text1" id= " UserName "size=" "Maxlength=" value=${user.username}></td></tr>

page Show we used the EL An expression that is more than the previous fetch user value=<%=user.getusername ()%>> to be simple, but to be clear, we are using JavaBean Private member variables in class , is no longer getUserId property.

Summary:

through some detailed understanding , recognizing that javabean mvc javabean

in the MVC Design model, it is model, also known as models , in the general program , We call it the data layer . , is to set the properties of the data and some behavior Get with the set.

Three questions JavaBean