Using generics to extract DAO layers, plus transaction annotation issues (Java.lang.Class cannot be cast to Java.lang.reflect.ParameterizedType)

To use generics to extract Basedao layers, there are problems in simplifying operations:

@Transactional this annotation can be inherited, so you want to write on the extracted Basedao layer, so that the implementation of the class can not write @transactional, you can open the transaction.

Problem Description:

Due to laziness, did not give Basedao suction interface, the code is as follows:

Package Com.liang.ssh2.base;import Java.lang.reflect.parameterizedtype;import Java.util.collections;import Java.util.list;import Javax.annotation.resource;import Org.hibernate.query;import Org.hibernate.Session;import Org.hibernate.sessionfactory;import Org.springframework.transaction.annotation.transactional;import Com.liang.ssh2.config.configuration;import Com.liang.ssh2.entity.page;import com.liang.ssh2.util.QueryHelper;@ Transactional@suppresswarnings ("Unchecked") public class basedao<t>{@Resourceprivate sessionfactory Sessionfactory; Class <T> clazz;/** * Gets the parameter type by Reflection */public Basedaoimpl () {System.out.println (this); Parameterizedtype pt = (parameterizedtype) this.getclass (). Getgenericsuperclass (); clazz= (class<t>) Pt.getactualtypearguments () [0];} /** * Gets the currently available session * @return */protected session getsession () {return sessionfactory.getcurrentsession ();} /* (non-javadoc) * @see com.liang.ssh2.base.basedao#save (t) */public void Save (t entity) {getsession (). Save (entity); /*(non-javadoc) * @see Com.liang.ssh2.base.basedao#getbyid (java.lang.Long) */public T getById (Long ID) {if (id==null) Return Null;return (T) getsession (). Get (Clazz, id);} /* (non-javadoc) * @see com.liang.ssh2.base.basedao#update (t) */public void update (t entity) {getsession (). Update ( entity);} /* (non-javadoc) * @see com.liang.ssh2.base.basedao#delete (java.lang.Long) */public void Delete (Long id) {if (id!=null) { Object Entity=getbyid (ID), if (entity!=null) {getsession (). Delete (entity);}} /* (non-javadoc) * @see com.liang.ssh2.base.basedao#getbyids (java.lang.long[]) */public list<t> getByIds (Long[] IDS) {if (ids==null| | ids.length==0) {return collections.empty_list;} Return GetSession (). CreateQuery (//"from" +clazz.getsimplename () + "where ID in (: IDs)")//.setparameterlist ("IDs", IDs) . List ();} /* (non-javadoc) * @see com.liang.ssh2.base.basedao#findall () */public list<t> findAll () {return getsession (). CreateQuery (//"from" +clazz.getsimplename ())//.list ();} /* (non-javadoc) * @see com.liang.ssh2.baSe. Basedao#getpage (Long, Java.lang.Long, com.liang.ssh2.util.QueryHelper) */public Page getpage (Long Currentpage,long Pagesize,queryhelper queryhelper) {//If the user does not specify pageSize dynamically, read the configuration file if (pagesize==null) {pagesize= Configuration.getpagesize ();} Get parameter list<object> parameters = Queryhelper.getparameters (); Query query = getsession (). CreateQuery (QUERYHELPER.GETQUERYLISTHQL ()); if (Parameters!=null&¶meters.size () >0 {for (int i = 0; i < parameters.size (); i++) {Query.setparameter (I, Parameters.get (i));}} Query.setfirstresult ((int) ((currentPage-1) *pagesize)); Query.setmaxresults (Pagesize.intvalue ()); List recordlist = Query.list ();//query = GetSession () for total number of records. CreateQuery (QUERYHELPER.GETQUERYCOUNTHQL ()); Note the space! if (Parameters! = null && parameters.size () > 0) {//Set parameter for (int i = 0; i < parameters.size (); i++) {Query . Setparameter (I, Parameters.get (i));}} Long RecordCount = (long) query.uniqueresult (); Query return new Page (CurrentPage, PageSize, RecordCount, recordlist);}}

Use the following:

Package Com.liang.ssh2.service.impl;import Org.springframework.stereotype.service;import Com.liang.ssh2.base.basedao;import Com.liang.ssh2.entity.User; @Servicepublic class Userserviceimpl extends Basedao <user>{}

notice I put @transactional on the Basedao, because @transactional can inherit, so Userserviceimpl is not put

When you start the server, you get an error: Caused By:java.lang.ClassCastException:java.lang.Class cannot is cast to Java.lang.reflect.ParameterizedType

Why is that?

Test a half-day discovery, error on the Basedao on the note:@Transactional , the reason is not very clear!!!

Two solutions:

First, directly Basedao on the @transactional annotations, in the implementation of the class added @transactional, for this example, in Userserviceimpl plus @transactional can open the transaction, will not error!

Second, do not lazy, obediently to Basedao to smoke an interface bar, and nothing else to change, @Transactional or can still inherit, modify the code as follows:

Package Com.liang.ssh2.base;import Java.util.list;import Com.liang.ssh2.entity.page;import Com.liang.ssh2.util.queryhelper;public interface Basedao<t> {/** * Save entity * @param entity */public abstract void Save ( t entity);/** * Get entity based on ID * @param ID * @return */public abstract T getById (Long ID);p ublic abstract void update (T entity); public abstract void Delete (Long id);p ublic abstract list<t> getbyids (long[] IDs);p ublic abstract list<t> fin DAll ();/** *  Get page * @param currentpage * @param pageSize//If the user does not dynamically specify PageSize (NULL), read the configuration file * @param queryhelper * @ Return */public abstract Page getpage (long currentpage, long Pagesize,queryhelper queryhelper);}

Package Com.liang.ssh2.base;import Java.lang.reflect.parameterizedtype;import Java.util.collections;import Java.util.list;import Javax.annotation.resource;import Org.hibernate.query;import Org.hibernate.Session;import Org.hibernate.sessionfactory;import Org.springframework.transaction.annotation.transactional;import Com.liang.ssh2.config.configuration;import Com.liang.ssh2.entity.page;import com.liang.ssh2.util.QueryHelper;@ Transactional@suppresswarnings ("Unchecked") public class Basedaoimpl<t> implements basedao<t>{@ Resourceprivate sessionfactory sessionfactory; Class <T> clazz;/** * Gets the parameter type by Reflection */public Basedaoimpl () {System.out.println (this); Parameterizedtype pt = (parameterizedtype) this.getclass (). Getgenericsuperclass (); clazz= (class<t>) Pt.getactualtypearguments () [0];} /** * Gets the currently available session * @return */protected session getsession () {return sessionfactory.getcurrentsession ();} /* (non-javadoc) * @see com.liang.ssh2.base.basedao#save (t) */public void Save (T entity{getsession (). Save (entity);} /* (non-javadoc) * @see Com.liang.ssh2.base.basedao#getbyid (java.lang.Long) */public T getById (Long ID) {if (id==null) Return Null;return (T) getsession (). Get (Clazz, id);} /* (non-javadoc) * @see com.liang.ssh2.base.basedao#update (t) */public void update (t entity) {getsession (). Update ( entity);} /* (non-javadoc) * @see com.liang.ssh2.base.basedao#delete (java.lang.Long) */public void Delete (Long id) {if (id!=null) { Object Entity=getbyid (ID), if (entity!=null) {getsession (). Delete (entity);}} /* (non-javadoc) * @see com.liang.ssh2.base.basedao#getbyids (java.lang.long[]) */public list<t> getByIds (Long[] IDS) {if (ids==null| | ids.length==0) {return collections.empty_list;} Return GetSession (). CreateQuery (//"from" +clazz.getsimplename () + "where ID in (: IDs)")//.setparameterlist ("IDs", IDs) . List ();} /* (non-javadoc) * @see com.liang.ssh2.base.basedao#findall () */public list<t> findAll () {return getsession (). CreateQuery (//"from" +clazz.getsimplename ())//.list ();} /* (non-jAvadoc) * @see com.liang.ssh2.base.basedao#getpage (Long, Java.lang.Long, Com.liang.ssh2.util.QueryHelper) */public Page getpage (Long currentpage,long pagesize,queryhelper queryhelper) {//If the user does not specify pageSize dynamically, read the configuration file if (pagesize==null ) {pagesize=configuration.getpagesize ();} Get parameter list<object> parameters = Queryhelper.getparameters (); Query query = getsession (). CreateQuery (QUERYHELPER.GETQUERYLISTHQL ()); if (Parameters!=null&¶meters.size () >0 {for (int i = 0; i < parameters.size (); i++) {Query.setparameter (I, Parameters.get (i));}} Query.setfirstresult ((int) ((currentPage-1) *pagesize)); Query.setmaxresults (Pagesize.intvalue ()); List recordlist = Query.list ();//query = GetSession () for total number of records. CreateQuery (QUERYHELPER.GETQUERYCOUNTHQL ()); Note the space! if (Parameters! = null && parameters.size () > 0) {//Set parameter for (int i = 0; i < parameters.size (); i++) {Query . Setparameter (I, Parameters.get (i));}} Long RecordCount = (long) query.uniqueresult (); Query return new Page (CurrentPage, PagesizE, RecordCount, recordlist);}} 

</pre><pre name= "code" class= "java" >package Com.liang.ssh2.service.impl;import Org.springframework.stereotype.service;import Com.liang.ssh2.base.basedaoimpl;import Com.liang.ssh2.entity.User; @Servicepublic class Userserviceimpl extends basedaoimpl<user>{}

Want to steal a lazy, less write an interface, also not easy AH!!!!!

Using generics to extract DAO layers, plus transaction annotation issues (Java.lang.Class cannot be cast to Java.lang.reflect.ParameterizedType)