Use reflection to assign values to the corresponding entity class's properties after reading from the database

1. Connect the database and close the connection (Jdbctools.java)

Package Com.xiaojie.dao;import Java.io.ioexception;import Java.sql.connection;import java.sql.PreparedStatement; Import Java.sql.resultset;import Java.sql.sqlexception;import Javax.sql.datasource;import      Com.mchange.v2.c3p0.combopooleddatasource;public class Jdbctools {private static DataSource ds=null;      The database connection pool should be initialized only once static{ds=new Combopooleddatasource ("helloc3p0");          }//Get database connection public static Connection getconnection () throws ClassNotFoundException, SQLException, ioexception{          return Ds.getconnection (); } public static void Shifanglianjie (Connection ct, preparedstatement ps,resultset rs) {if (rs!=null) {try {RS.C Lose ();}    catch (SQLException e) {//TODO auto-generated catch Blocke.printstacktrace ();}    } if (Ps!=null) {try {ps.close ();} catch (SQLException e) {//TODO auto-generated catch Blocke.printstacktrace ();} } if (Ct!=null) {try {ct.close ()} catch (SQLException e) {//TODO auto-generated catch BLOCKE.PRintstacktrace ();} }    }}

2. DAO Module

Package Com.xiaojie.dao;import Java.io.ioexception;import Java.sql.connection;import java.sql.PreparedStatement; Import Java.sql.resultset;import java.sql.resultsetmetadata;import java.sql.statement;import java.util.ArrayList; Import Java.util.date;import java.util.hashmap;import Java.util.list;import Java.util.map;import Com.xiaojie.beans.trade;import Java.sql.sqlexception;public class Dao<t> {//query a record, return the corresponding object public <T> T Query (class<t> clazz,string sql,object...args) {T example=null; Connection Ct=null; PreparedStatement Ps=null; ResultSet Rs=null;try {//1, get connectionct=jdbctools.getconnection (); SYSTEM.OUT.PRINTLN ("Query gets connected to the database");//2, get Preparedstatementps=ct.preparestatement (SQL);//3, fill placeholder for (int i=0;i <args.length;i++) {ps.setobject (i+1, args[i]);} 4, make inquiries, get Resultsetrs=ps.executequery ();//5, prepare a map<string,object>:(if the result set should be recorded) if (Rs.next ()) {map< String,object> values=new hashmap<string,object> ();//6, ResultSetMetaData object ResultSetMetaData rsd= Rs.getmEtadata ();//7, handles resultset, moves the pointer down one unit//8, the ResultSetMetaData object gets the number of columns in the result set, int lieshu=rsd.getcolumncount ();//9, The alias of each column is obtained by the ResultSetMetaData object, and the value for each column is given by resultset for (int i=0;i<lieshu;i++) {String Lieming=rsd.getcolumnlabel (i +1); object Liezhi=rs.getobject (i+1);//10, fill Map Object Values.put (Lieming,liezhi);} 11. Create a class corresponding Object Example=clazz.newinstance () with reflection,//12, traverse the Map object, fill the object's attribute value with reflection, for (map.entry<string, object> ent : Values.entryset ()) {String name=ent.getkey (); Object value=ent.getvalue ();//With Reflection assignment Reflectionutils.setfieldvalue ( example, name, value);}}} catch (Exception e) {e.printstacktrace ();} Finally{jdbctools.shifanglianjie (CT, PS, RS);} return example;} Querying multiple records, returning multiple corresponding objects public list<t> querylist (class<t> clazz,string sql,object...args) {T example=null; Connection Ct=null; PreparedStatement Ps=null; ResultSet Rs=null; List li=new ArrayList (); try {//1, get connectionct=jdbctools.getconnection (); System.out.println ("Querylist gets a connection to the database");//2, get Preparedstatementps=ct.preparestatement (SQL);//3, fill placeholder For (int i=0;i<args.length;i++) {ps.setobject (i+1, args[i]);} 4, make inquiries, get Resultsetrs=ps.executequery ();//5, prepare a map<string,object>:(if the result set is recorded) while (Rs.next ()) {Map <String,Object> values=new hashmap<string,object> ();//6, get ResultSetMetaData object ResultSetMetaData rsd= Rs.getmetadata ();//7, handles resultset, moves the pointer down one unit//8, the ResultSetMetaData object gets the number of columns in the result set, int lieshu=rsd.getcolumncount (); /9, the alias of each column is obtained by the ResultSetMetaData object, and the value of each column is given by resultset for (int i=0;i<lieshu;i++) {String lieming= Rsd.getcolumnlabel (i+1); object Liezhi=rs.getobject (i+1);//10, fill Map Object Values.put (Lieming,liezhi);} 11. Create a class corresponding Object Example=clazz.newinstance () with reflection,//12, traverse the Map object, fill the object's attribute value with reflection, for (map.entry<string, object> ent : Values.entryset ()) {String name=ent.getkey (); Object value=ent.getvalue ();//With Reflection assignment Reflectionutils.setfieldvalue ( example, name, value);} Li.add (example);}} catch (Exception e) {e.printstacktrace ();} Finally{jdbctools.shifanglianjie (CT, PS, RS);} return li;}}

3. Reflective Tool Class

Package Com.xiaojie.dao;import Java.lang.reflect.field;import Java.lang.reflect.invocationtargetexception;import Java.lang.reflect.method;import Java.lang.reflect.modifier;import Java.lang.reflect.parameterizedtype;import java.lang.reflect.type;/** * reflected Utils function set * Provides access to private variables, gets generic type class, extracts Utils functions such as element properties in the collection * @author Administrator * */PUBL IC class Reflectionutils {/** * through reflection, gets the type of the generic parameter of the parent class declared when the class is defined * such as: public EmployeeDAO extends Basedao<employee, Strin g> * @param clazz * @param index * @return */@SuppressWarnings ("unchecked") public static Class Getsuperclassgenrictype ( Class clazz, int index) {Type gentype = Clazz.getgenericsuperclass (); Gentype instanceof Parameterizedtype) {return object.class;} Type [] params = ((Parameterizedtype) gentype). Getactualtypearguments (); if (index >= params.length | | Index < 0) { return object.class;} if (! ( Params[index] instanceof Class) {return object.class;} Return (Class) Params[index];} /** * Through reflection, get the generic parameter type of the parent class declared in the class definition * such as: public EMPLoyeedao extends Basedao<employee, string> * @param <T> * @param clazz * @return */@SuppressWarnings ("Unchecke D ") Public static<t> class<t> Getsupergenerictype (Class clazz) {return Getsuperclassgenrictype (clazz, 0);} /** * cycle up, get Declaredmethod * @param object * @param methodName * @param parametertypes * @return */public static M Ethod Getdeclaredmethod (Object object, String methodName, class<?>[] parametertypes) {for (class<?> Superclass = Object.getclass (); Superclass! = Object.class; Superclass = Superclass.getsuperclass ()) {try {//superclass.getmethod (methodName, parametertypes); return Superclass.getdeclaredmethod (MethodName, parametertypes);} catch (Nosuchmethodexception e) {//method is not in the current class definition, continue to transition upward}//...} return null;} /** * makes filed accessible * @param field */public static void makeaccessible (Field field) {if (! Modifier.ispublic (Field.getmodifiers ())) {field.setaccessible (true);}} /** * cycle up, get Declaredfield * @param object * @param filedname * @reTurn */public static Field Getdeclaredfield (Object object, String filedname) {for (class<?> superclass = Object.getclass (); Superclass! = Object.class; Superclass = Superclass.getsuperclass ()) {try {return Superclass.getdeclaredfield (filedname);} catch ( Nosuchfieldexception e) {//field is not in the current class definition, continue to transition upward}}return null;}  /** * Call object method directly, ignoring modifier (private, Protected) * @param object * @param methodName * @param parametertypes * @param parameters * @return * @throws invocationtargetexception * @throws illegalargumentexception */public static Object InvokeMethod (Ob Ject object, String methodName, class<?> [] parametertypes,object [] parameters) throws invocationtargetexception{ METHOD = Getdeclaredmethod (object, MethodName, parametertypes); if (method = = null) {throw new IllegalArgumentException ("Could not Find method [" + MethodName + "] on target [" + Object + "]");} Method.setaccessible (true); try {return Method.invoke (object, parameters);} catch (Illegalaccessexception e) { System.out. println ("an exception that cannot be thrown");} return null;} /** * Directly Sets object property values, ignores private/protected modifiers, and does not pass Setter * @param object * @param fieldName * @param value */public static V OID SetFieldValue (Object object, String fieldName, Object value) {Field field = Getdeclaredfield (object, FieldName), if (fi Eld = = null) throw new IllegalArgumentException ("Could not the Find field [" + FieldName + "] on target [" + Object + "]"); Accessible (field); try {Field.set (object, value);} catch (Illegalaccessexception e) {System.out.println ("exception not possible to throw");}} /** * Directly reads the object's property values, ignores the private/protected modifier, and does not go through getter * @param object * @param fieldName * @return */public static objec T GetFieldValue (Object object, String fieldName) {Field field = Getdeclaredfield (object, FieldName); if (Field = = null) thro W New IllegalArgumentException ("Could not find field [" + FieldName + "] on target [" + Object + "]"); Makeaccessible (field Object result = Null;try {result = Field.get (Object),} catch (Illegalaccessexception e) {System.out.println ("cannot throwException ");} return result;}}

4, the database corresponding to the JavaBeans entity class

Package Com.xiaojie.beans;import Java.util.date;public class Trade {private int tradeid;private int userid;private Date t radetime;public int Gettradeid () {return tradeid;} public void Settradeid (int tradeid) {This.tradeid = TradeID;} public int GetUserid () {return userid;} public void Setuserid (int userid) {this.userid = userid;} Public Date Gettradetime () {return tradetime;} public void Settradetime (Date tradetime) {this.tradetime = Tradetime;}  Public trade (int tradeid, int userid, Date tradetime) {super (); This.tradeid = Tradeid;this.userid = Userid;this.tradetime = Tradetime;} Public trade () {super ();}}

5, write a test class to try the effect (if the imported jar package is imported, and the database has a corresponding JavaBeans table, c3p0 configuration files, etc. are all set up)

Package Com.xiaojie.test;import Java.io.ioexception;import Java.sql.date;import java.sql.sqlexception;import Java.util.arraylist;import Java.util.list;import Org.junit.test;import Com.xiaojie.beans.trade;import Com.xiaojie.dao.dao;public class Daotest {private DAO dao=new dao (); <span style= "White-space:pre" ></span> The following test method is to test an attribute assignment that queries a record from the database to the corresponding JavaBean, and displays a print result @testpublic void Testquery () throws classnotfoundexception in the console, SQLException, ioexception{string sql= "SELECT * from trade where tradeid=?"; Trade trade=new Trade (), trade= (trade) dao.query (trade.class,sql,1); System.out.println ("TradeID:" +trade.gettradeid () + "\nuserid:" +trade.getuserid () + "\ntradetiem:" + Trade.gettradetime ());} The following test method is to assign a value to the corresponding JavaBean property from the results of a database query (more than one record) and display multiple print results @testpublic void testquerylist () {String sql= "select *) in the console from trade "; Trade trade=new Trade (); List<trade>trades=new arraylist<trade> (); trades= (list<trade>) dao.querylist (Trade.class,sql); for (trade trade1:trades) {SYSTEM.OUT.PRINtln ("TradeID:" +trade1.gettradeid () + "\nuserid:" +trade1.getuserid () + "\ntradetiem:" +trade1.gettradetime ());}} 

Use reflection to assign values to the corresponding entity class's properties after reading from the database