【原創】基於註解運行時動態ORM映射

因爲當前項目採用了分表策略，故一個實體會對應多個相同結構的表。只是映射的表名不同而已~項目又使用憨包兒呢特（Hibernate），讓我採用原生SQL總感受不是那麼爽，咋辦呢？！第一念頭就是若是可以動態映射就好啦，也就是如今想查table1只需將實體對應的 table映射爲table1便可。咋個實現動態映射呢？！也就是須要動態改變類的註解。又咋個可以動態改變類的註解呢？！本質上修改字節碼，從新加載類便可，也就是所謂的字節碼加強功能~  看都看不懂字節碼咋個修改呢？！仍是須要站在巨人的肩上才行。ASM以及JDK自帶的字節碼加強都不用，立刻想到CGlib,javassist。。。仍是痛苦的折騰了良久，爲了你們不走個人彎路~ 直接上代碼先~

動態映射代碼以下:

 1: public class ClassPoolUtils {

 2: 

 3: 

 4:     /**

 5:  * 動態ORM映射

 6:  * 

 7:  * @param entityClassName 待映射的實體全限定類名

 8:  * @param tableName 待映射的表名

 9:  * @return 映射後的類對象

 10:  */

 11:     public static Class<?> tableMapping(String entityClassName, String tableName){

 12:         Class<?> c = null;

 13:         try {

 14:             ClassPool classPool = ClassPool.getDefault();

 15:             classPool.appendClassPath(new ClassClassPath(ClassPoolUtils.class));

 16:             classPool.importPackage("javax.persistence");

 17:             CtClass clazz = classPool.get(entityClassName);

 18:             ClassFile classFile = clazz.getClassFile();

 19: 

 20:             System.out.println("加強前Entity01:" + clazz.getAnnotation(Entity.class));

 21:             System.out.println("加強前Table02:" + clazz.getAnnotation(Table.class));

 22: 

 23:             ConstPool constPool = classFile.getConstPool();

 24:             Annotation tableAnnotation = new Annotation("javax.persistence.Table", constPool);

 25:             tableAnnotation.addMemberValue("name", new StringMemberValue(tableName, constPool));

 26:             // 獲取運行時註解屬性

 27:             AnnotationsAttribute attribute = (AnnotationsAttribute)classFile.getAttribute(AnnotationsAttribute.visibleTag);

 28:             attribute.addAnnotation(tableAnnotation);

 29:             classFile.addAttribute(attribute);

 30:             classFile.setVersionToJava5();

 31:             //clazz.writeFile();

 32: 

 33:             System.out.println("加強後Entity001:" + clazz.getAnnotation(Entity.class));

 34:             System.out.println("加強後Table002:" + clazz.getAnnotation(Table.class));

 35:             //TODO 當前ClassLoader中必須還沒有加載該實體。（同一個ClassLoader加載同一個類只會加載一次）

 36:             c = clazz.toClass();

 37:             System.out.println("加強後toClass-Entity0001:" + c.getAnnotation(Entity.class));

 38:             System.out.println("加強後toClass-Table0002:" + c.getAnnotation(Table.class));

 39:         } catch (Exception e) {

 40:             e.printStackTrace();

 41:         }

 42: 

 43:         return c;

 44:     }

 45:  

 46:     public static void main(String[] args) {

 47:           ClassPoolUtils.tableMapping("com.andy.model.Order", "order1");

 48:     }

執行結果:

 1: 加強前Entity01:@javax.persistence.Entity

 2: 加強前Table02:null

 3: 加強後Entity001:@javax.persistence.Entity

 4: 加強後Table002:@javax.persistence.Table(name="order1")

 5: 加強後toClass-Entity0001:@javax.persistence.Entity(name=)

 6: 加強後toClass-Table0002:@javax.persistence.Table(schema=, catalog=, uniqueConstraints=[], name=order1)