Hibernate O/R mapping simulation

As an important link in ssh, it is necessary to understand Hibernate's implementation of the O/R mapping.

The main use of the Java reflection mechanism to obtain a complete SQL statement.

Preparatory work:

1. Object

Student Entity classes:

 Public classStudent {Private intID; PrivateString name; Private intAge ;  Public intgetId () {returnID; }     Public voidSetId (intID) { This. ID =ID; }     PublicString GetName () {returnname; }     Public voidsetName (String name) { This. Name =name; }     Public intGetage () {returnAge ; }     Public voidSetage (intAge ) {         This. Age =Age ; }}

2. Relationship

_student table:

-- database:hibernate Create Table int Primary Key int varchar ());

3. Analog O/R Mapping:

Sessionstu for the Student entity class (to complete the persistence of the student object):

 Public classSessionstu {PrivateString TableName; Privatemap<string, string> field2column =NewHashmap<string,string>(); Privatestring[] fields;  PublicSessionstu () {//The following should be build out by parsing the XML//This example demonstrates only the core part of Hibernate: O/R Mapping (full SQL with Reflection)TableName = "_student"; Field2column.put ("id", "_id"); Field2column.put ("Name", "_name"); Field2column.put ("Age", "_age"); fields=Newstring[field2column.size ()]; Try{class.forname ("Com.mysql.jdbc.Driver"); } Catch(ClassNotFoundException e) {//TODO auto-generated Catch blockE.printstacktrace (); }    }         Public voidSave (Student Student)throwsException {//TODO auto-generated Method StubString sql =Createsql (); Connection Conn= Drivermanager.getconnection ("Jdbc:mysql://localhost:3306/hibernate", "Root", "" "); PreparedStatement PS=conn.preparestatement (SQL); PS=setparameters (ps,student);        Ps.executeupdate ();        Ps.close ();    Conn.close (); }        //Important    PrivatePreparedStatement setparameters (preparedstatement PS, Student Student)throwsexception{ for(inti = 0; i < fields.length; i++) {String Get_method= "Get" + (Char) (Fields[i].charat (0) -32) +fields[i].substring (1); Method m = student.getclass (). GetMethod (Get_method); String type = M.getreturntype (). GetName (); String te= Type.substring (Type.lastindexof (".") +1); Switch(TE) { Case"Int": Ps.setint (i+1, (int) M.invoke (student));  Break;  Case"String": ps.setstring (i+1, (String) M.invoke (student)); default:                 Break; }        }        returnPS; }        Privatestring Createsql () {string Columnsstr= ""; intindex = 0;  for(String key:field2Column.keySet ()) {Fields[index]=key; Columnsstr+ = (Field2column.get (key) + ","); Index++; } columnsstr= columnsstr.substring (0, Columnsstr.length ()-1); String unknow = "";  for(inti = 0; I < field2column.size (); i++) {Unknow+= "?,"; } unknow= Unknow.substring (0,unknow.length ()-1); String SQL= "INSERT INTO" + This. TableName + "(" + Columnsstr + ") VALUES (" + Unknow + ")";        SYSTEM.OUT.PRINTLN (SQL); returnSQL; }    }

4. Test:

 Public class Testsessionsave {    publicstaticvoidthrows  Exception {         New  Student ();        Student.setage (a);        Student.setid (5);        Student.setname ("Hibernate");         New Sessionstu ();        Ss.save (student);    }}

5. Done

Hibernate O/R mapping simulation