java - CriteriaBuilder in JPA - where clause -

am new jpa. building select query clause. need select table contacts contactname's equals value of string name.

used code below create db table:

create table contacts ( contactid bigint unsigned not null primary key auto_increment, contactname varchar(100) not null, contactemailid varchar(100) not null,  username varchar(100) not null,  index contact_names (contactname)  ) engine = innodb; 

following entity class;

     @entity     private string username;       @id     @generatedvalue(strategy = generationtype.identity)     @column(name = "contactid")      public long getcontactid() {         return contactid;     }      public void setcontactid(long contactid) {         contactid = contactid;     }       @basic     @column(name = "username")     public string getusername() {     return username;     }      public void setusername(string username) {     this.username = username;     } 

following contactservlet class code trying write criteriabuilder code.

         entitymanager manager = null;          entitytransaction transaction = null;          try{          manager = this.factory.createentitymanager();         transaction = manager.gettransaction();         transaction.begin();        criteriabuilder cb = manager.getcriteriabuilder();        criteriaquery<contact> q1 = cb.createquery(contact.class);        root<contact> postroot = q1.from(contact.class);         q1.select(postroot).where(cb.equal(postroot.get("username"), name));        typedquery<contact> qry = manager.createquery(q1);         list<contact> result = qry.getresultlist();         (contact contactinstance : result)           {           dbcontactname = contactinstance.getcontactname().trim();          dbcontactemail = contactinstance.getcontactemailid().trim(); 

.....

don't know going wrong??

following error while executing project: java.lang.illegalargumentexception: unable resolve attribute [username] against path @ org.hibernate.jpa.criteria.path.abstractpathimpl.unknownattribute(abstractpathimpl.java:117) @ org.hibernate.jpa.criteria.path.abstractpathimpl.locateattribute(abstractpathimpl.java:214) @ org.hibernate.jpa.criteria.path.abstractpathimpl.get(abstractpathimpl.java:185) @ com.contactservlet.dopost(contactservlet.java:110) @ javax.servlet.http.httpservlet.service(httpservlet.java:644) @ javax.servlet.http.httpservlet.service(httpservlet.java:725) @ org.apache.catalina.core.applicationfilterchain.internaldofilter(applicationfilterchain.java:291) @ org.apache.catalina.core.applicationfilterchain.dofilter(applicationfilterchain.java:206) @ org.apache.tomcat.websocket.server.wsfilter.dofilter(wsfilter.java:52) @ org.apache.catalina.core.applicationfilterchain.internaldofilter(applicationfilterchain.java:239) @ org.apache.catalina.core.applicationfilterchain.dofilter(applicationfilterchain.java:206) @ org.apache.catalina.core.standardwrappervalve.invoke(standardwrappervalve.java:219) @ org.apache.catalina.core.standardcontextvalve.invoke(standardcontextvalve.java:106) @ org.apache.catalina.authenticator.authenticatorbase.invoke(authenticatorbase.java:505) @ org.apache.catalina.core.standardhostvalve.invoke(standardhostvalve.java:142) @ org.apache.catalina.valves.errorreportvalve.invoke(errorreportvalve.java:79) @ org.apache.catalina.valves.abstractaccesslogvalve.invoke(abstractaccesslogvalve.java:610) @ org.apache.catalina.core.standardenginevalve.invoke(standardenginevalve.java:88) @ org.apache.catalina.connector.coyoteadapter.service(coyoteadapter.java:534) @ org.apache.coyote.http11.abstracthttp11processor.process(abstracthttp11processor.java:1081) @ org.apache.coyote.abstractprotocol$abstractconnectionhandler.process(abstractprotocol.java:658) @ org.apache.coyote.http11.http11nioprotocol$http11connectionhandler.process(http11nioprotocol.java:222) @ org.apache.tomcat.util.net.nioendpoint$socketprocessor.dorun(nioendpoint.java:1566) @ org.apache.tomcat.util.net.nioendpoint$socketprocessor.run(nioendpoint.java:1523) @ java.util.concurrent.threadpoolexecutor.runworker(threadpoolexecutor.java:1142) @ java.util.concurrent.threadpoolexecutor$worker.run(threadpoolexecutor.java:617) @ org.apache.tomcat.util.threads.taskthread$wrappingrunnable.run(taskthread.java:61) @ java.lang.thread.run(thread.java:745)

try with:

q1.select(postroot).where(cb.equal(postroot.get("username"), name)); 

the u of username attribute in lower case.