java如何把数据库数据转成枚举
1、查询数据库数据，这里我直接初始化一个List集合
2、创建EnumDemo类
3、新增动态添加枚举类型的公共方法，我将在最后一步贴出完整代码
4、遍历数据库查出来的字典数据，加入枚举中
5、输出并验证
6、package com.ly.ed;
import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import sun.reflect.ConstructorAccessor;
import sun.reflect.FieldAccessor;
import sun.reflect.ReflectionFactory;
public class EnumService {
public static void main(String[] args) {
//1、数据库查询
// List<Map<String, Object>> dataList = daoc.queryData(...);
List<Map<String, Object>> dataList = new ArrayList<Map<String, Object>>();
dataList.add(new HashMap<String, Object>());
dataList.add(new HashMap<String, Object>());
dataList.add(new HashMap<String, Object>());
dataList.add(new HashMap<String, Object>());
dataList.get(0).put("KEY", "MON");
dataList.get(0).put("VALUE", 1);
dataList.get(1).put("KEY", "TUE");
dataList.get(1).put("VALUE", 2);
dataList.get(2).put("KEY", "WED");
dataList.get(2).put("VALUE", 3);
dataList.get(3).put("KEY", "THU");
dataList.get(3).put("VALUE", 4);
//2、添加枚举
for(Map<String, Object> map : dataList) {
addEnum(EnumDemo.class, map.get("KEY").toString(), map.get("VALUE"));
}
//3、打印验证
for (EnumDemo e : EnumDemo.values()) {
System.out.println(e.toString());
}
}
@SuppressWarnings("unchecked")
public static <T extends Enum<?>> void addEnum(Class<T> enumType, String name, Object value) {
// 0. Sanity checks
if (!Enum.class.isAssignableFrom(enumType)) {
throw new RuntimeException("class " + enumType + " is not an instance of Enum");
}
Field valuesField = null;
Field[] fields = EnumDemo.class.getDeclaredFields();
for (Field field : fields) {
if (field.getName().contains("$VALUES")) {
valuesField = field;
break;
}
}
AccessibleObject.setAccessible(new Field[] { valuesField }, true);
try {
// 2. Copy it
T[] previousValues = (T[]) valuesField.get(enumType);
List<T> values = new ArrayList<T>(Arrays.asList(previousValues));
// 3. build new enum
T newValue = (T) makeEnum(enumType, name, values.size(), new Class[]{Integer.class}, new Object[]{value});
// 4. add new value
values.add(newValue);
Object object = values.toArray((EnumDemo[]) Array.newInstance(EnumDemo.class, 0));
// 5. Set new values field
setFailsafeFieldValue(valuesField, null, object);
// 6. Clean enum cache
cleanEnumCache(EnumDemo.class);
} catch (Exception e) {
e.printStackTrace();
throw new RuntimeException(e.getMessage(), e);
}
}
private static void cleanEnumCache(Class<?> enumClass) throws NoSuchFieldException, IllegalAccessException {
blankField(enumClass, "enumConstantDirectory"); // Sun (Oracle?!?) JDK 1.5/6
blankField(enumClass, "enumConstants"); // IBM JDK
}
private static void blankField(Class<?> enumClass, String fieldName) throws NoSuchFieldException,IllegalAccessException {
for (Field field : Class.class.getDeclaredFields()) {
if (field.getName().contains(fieldName)) {
AccessibleObject.setAccessible(new Field[] { field }, true);
setFailsafeFieldValue(field, enumClass, null);
break;
}
}
}
private static void setFailsafeFieldValue(Field field, Object target, Object value) throws NoSuchFieldException,IllegalAccessException {
// let's make the field accessible
field.setAccessible(true);
// next we change the modifier in the Field instance to
// not be final anymore, thus tricking reflection into
// letting us modify the static final field
Field modifiersField = Field.class.getDeclaredField("modifiers");
modifiersField.setAccessible(true);
int modifiers = modifiersField.getInt(field);
// blank out the final bit in the modifiers int
modifiers &= ~Modifier.FINAL;
modifiersField.setInt(field, modifiers);
FieldAccessor fa = ReflectionFactory.getReflectionFactory().newFieldAccessor(field, false);
fa.set(target, value);
}
private static Object makeEnum(Class<?> enumClass, String value, int ordinal, Class<?>[] additionalTypes,
Object[] additionalValues) throws Exception {
Object[] parms = new Object[additionalValues.length + 2];
parms[0] = value;
parms[1] = Integer.valueOf(ordinal);
System.arraycopy(additionalValues, 0, parms, 2, additionalValues.length);
return enumClass.cast(getConstructorAccessor(enumClass, additionalTypes).newInstance(parms));
}
private static ConstructorAccessor getConstructorAccessor(Class<?> enumClass, Class<?>[] additionalParameterTypes)
throws NoSuchMethodException {
Class<?>[] parameterTypes = new Class[additionalParameterTypes.length + 2];
parameterTypes[0] = String.class;
parameterTypes[1] = int.class;
System.arraycopy(additionalParameterTypes, 0, parameterTypes, 2, additionalParameterTypes.length);
return ReflectionFactory.getReflectionFactory().newConstructorAccessor(enumClass.getDeclaredConstructor(parameterTypes));
}
}