java 動態生成bean的案例
阿新 • • 發佈:2021-02-21
最近做一個需求,需求中的bean只用於生成一次json使用,所以想通過配置來動態的生成,查了一下,java還真有這個實現。
java動態的生成javabean,只能生成屬性和對應的set/get方法,不能生成其他的方法。
import org.assertj.core.internal.cglib.beans.BeanGenerator; import org.assertj.core.internal.cglib.beans.BeanMap; import java.lang.reflect.Field; import java.lang.reflect.Method; import java.util.HashMap; import java.util.Iterator; import java.util.Map; import java.util.Set; /** * Created by wangpengzhi1 on 2018/1/2. */ public class BeanCeater { public static void main(String[] args) throws ClassNotFoundException { System.out.println("Generate JavaBean"); Map properties = new HashMap(); properties.put("id",Class.forName("java.lang.Integer")); properties.put("name",Class.forName("java.lang.String")); properties.put("address",Class.forName("java.lang.String")); Object stu = generateObject(properties); System.out.println("Set values"); setValue(stu,"id",123); setValue(stu,"name","454"); setValue(stu,"address","789"); System.out.println("Get values"); System.out.println(">> " + getValue(stu,"id")); System.out.println(">> " + getValue(stu,"name")); System.out.println(">> " + getValue(stu,"address")); System.out.println("Show all methods"); Method[] methods = stu.getClass().getDeclaredMethods(); for(Method method : methods) { System.out.println(">> " + method.getName()); } System.out.println("Show all properties"); Field[] fields = stu.getClass().getDeclaredFields(); for(Field field : fields) { System.out.println(">> " + field.getName()); } } private static Object generateObject(Map properties) { BeanGenerator generator = new BeanGenerator(); Set keySet = properties.keySet(); for(Iterator i = keySet.iterator(); i.hasNext();) { String key = (String)i.next(); generator.addProperty(key,(Class)properties.get(key)); } return generator.create(); } private static Object getValue(Object obj,String property) { BeanMap beanMap = BeanMap.create(obj); return beanMap.get(property); } private static void setValue(Object obj,String property,Object value) { BeanMap beanMap = BeanMap.create(obj); beanMap.put(property,value); } }
程式碼不難懂,有需要的自己複製。
補充:spring 工具類 ReflectionUtils 獲取bean所有欄位
以前遇到要獲取當前類以及所有父類的的field的時候,都是遞迴一直往上找,一直到Object ,個人覺得這種方法是不是太low了,有沒有更好的辦法?或者jdk其實是有這種方法的,只是我不知道,今天看了下spring中的實現,也是一樣的,真沒有更好的辦法?
public static void doWithFields(Class<?> clazz,ReflectionUtils.FieldCallback fc,@Nullable ReflectionUtils.FieldFilter ff) { Class targetClass = clazz; do { Field[] fields = getDeclaredFields(targetClass); Field[] var5 = fields; int var6 = fields.length; for(int var7 = 0; var7 < var6; ++var7) { Field field = var5[var7]; if (ff == null || ff.matches(field)) { try { fc.doWith(field); } catch (IllegalAccessException var10) { throw new IllegalStateException("Not allowed to access field '" + field.getName() + "': " + var10); } } } targetClass = targetClass.getSuperclass(); } while(targetClass != null && targetClass != Object.class); } private static Field[] getDeclaredFields(Class<?> clazz) { Assert.notNull(clazz,"Class must not be null"); Field[] result = (Field[])declaredFieldsCache.get(clazz); if (result == null) { try { result = clazz.getDeclaredFields(); declaredFieldsCache.put(clazz,result.length == 0 ? NO_FIELDS : result); } catch (Throwable var3) { throw new IllegalStateException("Failed to introspect Class [" + clazz.getName() + "] from ClassLoader [" + clazz.getClassLoader() + "]",var3); } } return result; }
以上為個人經驗,希望能給大家一個參考,也希望大家多多支援我們。如有錯誤或未考慮完全的地方,望不吝賜教。