Java reflection get annotations and Stitch SQL statements

First two annotations are Table and Column, respectively

 Package com.hk.test; Import Java.lang.annotation.ElementType; Import java.lang.annotation.Retention; Import Java.lang.annotation.RetentionPolicy; Import Java.lang.annotation.Target; @Target ({elementtype.type}) @Retention (retentionpolicy.runtime)  public @Interface  Table {    String value ();}

　　

 Package com.hk.test; Import Java.lang.annotation.ElementType; Import java.lang.annotation.Retention; Import Java.lang.annotation.RetentionPolicy; Import Java.lang.annotation.Target; @Target ({Elementtype.field}) @Retention (retentionpolicy.runtime)  public @Interface  Column {    String value ();}

Then create a new Bean Class Filter.java (this class can be changed according to your own needs, as long as the style is not changed)

 Packagecom.hk.test; @Table ("User") Public classFilter {@Column ("id")    Private intID; @Column ("User_name")    PrivateString UserName; @Column ("Age")    Private intAge ; @Column ("Email")    PrivateString Email;  Public intgetId () {returnID; }     Public voidSetId (intID) { This. ID =ID; }     PublicString GetUserName () {returnUserName; }     Public voidsetusername (String userName) { This. UserName =UserName; }     Public intGetage () {returnAge ; }     Public voidSetage (intAge ) {         This. Age =Age ; }     PublicString Getemail () {returnemail; }     Public voidsetemail (String email) { This. email =email; }    }

Then test the class

 Packagecom.hk.test;ImportJava.lang.reflect.Field;ImportJava.lang.reflect.Method;/** *  * @authorHk_z *@deprecatedreflection on a class get annotations and field names stitched into SQL statements *@version0.1*/ Public classTest { Public Static voidMain (string[] args) {Filter F1=NewFilter (); F1.setid (10); Filter F2=NewFilter (); F2.setusername ("Lucy");//Fuzzy QueryFilter f3=NewFilter (); F3.setemail ("[Email Protected],[email protected]");//any oneString SQL1=query (F1);        System.out.println (SQL1); String SQL2=query (F2);        System.out.println (SQL2); String Sql3=query (F3);    System.out.println (SQL3); }    Private StaticString Query (Filter F1) {//TODO auto-generated Method StubStringBuilder SB =NewStringBuilder (); //1. Get to ClassClass C =F1.getclass (); //2. Get the name of the table        Booleanexists = C.isannotationpresent (Table.class);//There are no table annotations in class        if(!exists) {            return NULL; } Table T= (table) c.getannotation (table).class); String TableName= T.value ();//Table nameSb.append ("SELECT * from"). Append (TableName). Append ("Where 1 = 1"); //3. Iterate through all the fieldsfield[] Farray =C.getdeclaredfields ();  for(Field field:farray) {//4. Handle the SQL for each field//4.1 Get field name            BooleanFexists = Field.isannotationpresent (Column.class); if(!fexists) {                Continue; } Column Column= Field.getannotation (Column.class); String ColumnName= Column.value ();//the name of the field inside the table//4.2 Get the value of the fieldString filedname = Field.getname ();//the name of the variableString getmethodname = "Get" +filedname.substring (0,1). toUpperCase () +filedname.substring (1); Object Fieldvalue=NULL; //Assemble get method to get return value;            Try{Method GetMethod= C.getmethod (Getmethodname);//ReflectionFieldvalue = Getmethod.invoke (F1);//Reflection Call                            } Catch(Exception e) {//TODO auto-generated Catch blockE.printstacktrace (); }            //4.3 assembling SQL            if(Fieldvalue = =NULL|| (FieldvalueinstanceofInteger && (integer) fieldvalue==0))            {                Continue; } sb.append ("and"). Append (Filedname); String [] Val=NULL; if(FieldvalueinstanceofString) {//string type and have commas to split                if((String) fieldvalue). Contains (",") ) {Val= (String) fieldvalue. Split (","); Sb.append ("In (");  for(String v:val) {sb.append ("'"). Append (v). Append ("'"). Append (","); } Sb.deletecharat (Sb.length ()-1); Sb.append (")"); }                Else{sb.append ("="). Append ("'"). Append (Fieldvalue). Append ("'"); }            }            Else if(FieldvalueinstanceofInteger) {Sb.append (" = "). Append (Fieldvalue); }                    }        returnsb.tostring (); }}

Java reflection get annotations and Stitch SQL statements