Java Annotations and reflections the practice of making DAO base classes

First of all, three annotations.

Primary key annotations

Package comments;import java.lang.annotation.Documented; import java.lang.annotation.elementtype;import java.lang.annotation.inherited; import java.lang.annotation.Retention; import Java.lang.annotation.retentionpolicy;import java.lang.annotation.target;/** * PRIMARY KEY * @author Administrator */@Target (Elementtype. FIELD) @Retention (retentionpolicy.runtime) @Documented @Inherited public @interface    key {}             

Package comments;import java.lang.annotation.Documented; import java.lang.annotation.elementtype;import java.lang.annotation.inherited; import java.lang.annotation.Retention; import Java.lang.annotation.retentionpolicy;import java.lang.annotation.target;/** * Set this note if not associated with data * @ Author Administrator * */@Target (Elementtype. FIELD) @Retention (retentionpolicy.runtime) @Documented @Inherited public @interface    notrecord {}             

Package comments;Import java.lang.annotation.Documented;Import Java.lang.annotation.ElementType;import java.lang.annotation.Inherited; import java.lang.annotation.Retention; import Java.lang.annotation.RetentionPolicy; import Java.lang.annotation.Target; /** * Set table name * @author  Administrator * */@Target (elementtype.type) @Retention ( Retentionpolicy.runtime) @Documented @Inherited public @interface Table {  public String name();}               

Then the custom exception class

package org;/** * 设置自定义异常 * @author  Administrator * */public class NumException extends Exception { private String name; public NumException(String name){ this.name=name; } public String toString(){ return name; }}

Entity class

package org;Import comments. Key;Import comments. Table;Import Comments.notrecord;@Table (name ="Student")PublicClassStudent {@Key Private String ID;private String name;@notRecordPrivate String sex;Privateint age;Public StringGetId() {return ID; }PublicvoidSetId(String ID) {This.id = ID; }Public StringGetName() {return name; }PublicvoidSetName(String name) {THIS.name = name; }public String getSex () {return sex;} public void setsex (String sex) {this.sex = sex;} public int getage () {return age;} public void setAge  (int age) {this.age = Age;}}   

class that processes entity classes to generate SQL.

Package Org;import Java.lang.reflect.field;import comments. Key;import comments.Table;import Comments.notrecord;publicClass Processing {/** * Generate INSERT INTO SQL statement from entity class * @param CL *@return* @throws illegalargumentexception * @throws illegalaccessexception * @throws numexception */Public StringSave (ObjectCL) throws IllegalArgumentException, Illegalaccessexception, numexception{String sql="INSERT into";IfCl!=null) {field[] fiels=Cl.getclass (). Getdeclaredfields ();Get collection of Reflected objects Boolean t=Cl.getclass (). Isannotationpresent (Table.Class);Get the class if there are annotationsif (t) {Tabletab=Cl.getclass (). Getannotation (Table.Class); sql+=Tab.name ();Get table name String name ="";Record field name String value ="";Record Value name Boolean bl=false;Record whether the primary key is emptyfor (FieldFl:fiels) {Cyclic assemblyFl.setaccessible (TRUE);Turn on access to a private variable Object tobj=Fl.GetCL);if (tobj!=null) {IfFl.isannotationpresent (Key.Class)) {Determine if there is a primary key bl=true; }if (!Fl.isannotationpresent (Notrecord.Class) {name+=Fl.getname () +","; value+="'" +tobj.ToString () +"‘,"; } } }if (BL) {if (name.Length () >0) name=name.substring (0,name.Length ()-1);if (value.Length () >0) value=value.substring (0,value.Length ()-1); sql+="(" +name+") VALUES (" +value+")"; }else throw new Numexception ("The class primary key cannot be empty" is not found); }else throw new Numexception ("Incoming object is not an entity class"); }else throw new Numexception ("Incoming object cannot be empty");Throw exceptionreturn SQL; }/** * Incoming Object update * @param obj *@return* @throws illegalargumentexception * @throws illegalaccessexception * @throws numexception */Public StringUpdate (Object obj) throws IllegalArgumentException, Illegalaccessexception, numexception{String sql="Update";if (obj!=null) {field[] Fiels=obj.getclass (). Getdeclaredfields ();Gets the collection of reflected objects, Boolean t=obj.getclass (). Isannotationpresent (Table.Class);Get the class if there are annotationsif (t) {TableTab=obj.getclass (). Getannotation (Table.Class); sql+=Tab.name () +"Set";Get Table name StringWH ="";Record Field name String k=""; Boolean bl=false;Record whether the primary key is emptyfor (FieldFl:fiels) {Cyclic assemblyFl.setaccessible (TRUE);Turn on access to a private variable Object tobj=Fl.Get (obj);if (tobj!=null) {IfFl.isannotationpresent (Key.Class)) {Determine if there is a primary key bl=true; k=Fl.getname () +"= '" +tobj.ToString () +"' Where";}else{if (!Fl.isannotationpresent (Notrecord.Class)) {wh+=Fl.getname () +"= '" +tobj.ToString () +"‘,"; } } } }if (BL) { if (wh.length () >0) wh=wh.substring (0,wh.Length ()-1); if (k.length () >0) k=k.substring (0,k.Length ()-1); sql+=k+wh;} Else throw new Numexception ("Cannot find class primary key primary key cannot be empty");} Else throw new Numexception ("Incoming object is not an entity class");} Else throw new Numexception ("Incoming object cannot be empty");  Throws an exception to return SQL;}}                 

Finally, the test class

package org;Import java.lang.annotation.Annotation;Import Java.lang.reflect.Field;Import comments.Table;import comments. Key; public class Temp {public static Span class= "Hljs-keyword" >void Main (string[] aa) throws IllegalArgumentException, Illegalaccessexception, numexception{Student stu=new Student ( ); Stu.setid ( "CCC"), Stu.setname ( "name"), Stu.setage (18); Stu.setsex ( "male"); //stu=null; System.out. println (new processing ().  Save (Stu)); System.out. println (new processing (). Update (Stu));}}    

Java Annotations and reflections the practice of making DAO base classes