利用反射如何动态生成sql

一.自定义注解 @UpdateWhere

@Target({ElementType.FIELD})                //作用于类
@Retention(RetentionPolicy.RUNTIME)        //运行时有效
@Documented                             //可以出现在文档里
@Inherited
public @interface UpdateWhere {

}

二.创建实体类接受

public class NameValuePair<Name, Value> implements Serializable {
	private static final long serialVersionUID = 1276809011610487148L;
	private Name name;
	private Value value;

	public NameValuePair() {
		super();
	}

	public NameValuePair(Name name, Value value) {
		super();
		this.name = name;
		this.value = value;
	}

	public Name getName() {
		return name;
	}

	public void setName(Name name) {
		this.name = name;
	}

	public Value getValue() {
		return value;
	}

	public void setValue(Value value) {
		this.value = value;
	}

	public NameValuePair<Name, Value> returnThis() {
		return this;
	}

}

三.动态sql生成

			throws ServiceException {
		try {
			Class<?> updateClazz = updateObject.getClass();
			// Table 是类上面是否有这个注解
			if (!Verify.isEmpty(id) || updateClazz == null || !updateClazz.isAnnotationPresent(Table.class)) {
				throw new ServiceException("参数异常!");
			}
			ArrayList<NameValuePair<String, Object>> whereList = new ArrayList<>(); // 条件list
			ArrayList<Object> sqlParams = new ArrayList<>(); // 参数list
			StringBuilder sqlBuffer = new StringBuilder("update " + updateClazz.getSimpleName() + " set ");
			// 开始解析
			// getDeclaredFields()：获得某个类的所有声明的字段，即包括public、private和proteced，但是不包括父类的申明字段
			for (Field declaredField : updateClazz.getDeclaredFields()) {
				if (declaredField.isAnnotationPresent(Id.class)) {
					continue; // ID不参与更新
				}
				if (!declaredField.isAnnotationPresent(Column.class)) {
					continue;
				}
				declaredField.setAccessible(Boolean.TRUE);
				String declaredFieldName = declaredField.getName();
				Object declaredFieldValue = declaredField.get(updateObject);
				if (declaredFieldValue == null || declaredFieldValue.toString().trim().length() < 1) {
					continue;
				}

				if (declaredField.isAnnotationPresent(UpdateWhere.class)) {
				//	whereList.add(new NameValuePair<>(declaredFieldName, declaredFieldValue));
					continue; // 更新的条件不参与更新
				}
				sqlBuffer.append(declaredFieldName).append("=?,");
				sqlParams.add(declaredFieldValue);
				declaredField.setAccessible(Boolean.FALSE);
			}
			if (!sqlBuffer.toString().endsWith(",")) {
			//	LOGGER.info("未检测到更新参数, 已生成的SQL: " + sqlBuffer + " ; 参数: " + updateObject);
			}
			/*
			 * sqlBuffer.deleteCharAt(sqlBuffer.length() -
			 * 1).append(" where 1=1, ");
			 */

//			if (whereList.size() < 1) {
//				throw new ServiceException("未检测到更新条件1, 已生成的SQL: " + sqlBuffer + ", 参数: " + updateObject);
//			}
			/*
			 * for (NameValuePair<String, Object> nameValuePair : whereList) {
			 * sqlBuffer.append(nameValuePair.getName()).append("=?,");
			 * sqlParams.add(nameValuePair.getValue()); }
			 */
			/*
			 * if (!sqlBuffer.toString().endsWith(",")) { throw new
			 * ServiceException("未检测到更新条件2, 已生成的SQL: " + sqlBuffer + ", 参数: " +
			 * updateObject); }
			 */
			String sqlString = sqlBuffer.append("updateTime=? ").append("  where  id= ?")
					.toString();
			sqlParams.add(updateTime);
			sqlParams.add(id);
			return new NameValuePair<>(sqlString, sqlParams.toArray());
		} catch (Exception e) {
			throw new ServiceException("生成hibernate更新的SQL异常, 参数: " + updateObject, e);
		}
	}

四.获取

 name:动态sql语句
 value;参数值