Java8通过Function获取字段名的步骤

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摘要：Java8通过Function获取字段名，解决硬编码，效果类似于mybatis-plus的LambdaQueryWrapper。

本文总共三个步骤：
1、使Function获取序列化能力；
2、通过SFunction获取字段名；
3、建一些业务代码进行测试；

使Function获取序列化能力

import java.io.Serializable;
import java.util.function.Function;

/**
 * 使Function获取序列化能力
 */
@FunctionalInterface
public interface SFunction<T, R> extends Function<T, R>, Serializable {
}

通过SFunction获取字段名

import java.lang.invoke.SerializedLambda;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class ColumnUtil {

  public static <T> String getName(SFunction<T, ?> fn) {
    // 从function取出序列化方法
    Method writeReplaceMethod;
    try {
      writeReplaceMethod = fn.getClass().getDeclaredMethod("writeReplace");
    } catch (NoSuchMethodException e) {
      throw new RuntimeException(e);
    }

    // 从序列化方法取出序列化的lambda信息
    boolean isAccessible = writeReplaceMethod.isAccessible();
    writeReplaceMethod.setAccessible(true);
    SerializedLambda serializedLambda;
    try {
      serializedLambda = (SerializedLambda) writeReplaceMethod.invoke(fn);
    } catch (IllegalAccessException | InvocationTargetException e) {
      throw new RuntimeException(e);
    }
    writeReplaceMethod.setAccessible(isAccessible);

    // 从lambda信息取出method、field、class等
    String fieldName = serializedLambda.getImplMethodName().substring("get".length());
    fieldName = fieldName.replaceFirst(fieldName.charAt(0) + "", (fieldName.charAt(0) + "").toLowerCase());
    Field field;
    try {
      field = Class.forName(serializedLambda.getImplClass().replace("/", ".")).getDeclaredField(fieldName);
    } catch (ClassNotFoundException | NoSuchFieldException e) {
      throw new RuntimeException(e);
    }

    // 从field取出字段名，可以根据实际情况调整
    TableField tableField = field.getAnnotation(TableField.class);
    if (tableField != null && tableField.value().length() > 0) {
      return tableField.value();
    } else {
      return fieldName.replaceAll("[A-Z]", "_$0").toLowerCase();
    }
  }
}

建一些业务代码进行测试

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * 字段名注解。测试用
 */
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface TableField {
  String value() default "";
}

import java.io.Serializable;

/**
 * 用户实体类。测试用
 */
public class User implements Serializable {

  private String loginName;

  @TableField("nick")
  private String nickName;

  public String getLoginName() {
    return loginName;
  }

  public void setLoginName(String loginName) {
    this.loginName = loginName;
  }

  public String getNickName() {
    return nickName;
  }

  public void setNickName(String nickName) {
    this.nickName = nickName;
  }
}

/**
 * 测试用
 */
public class Test {
  public static void main(String[] args) {
    System.out.println("字段名：" + ColumnUtil.getName(User::getLoginName));
    System.out.println("字段名：" + ColumnUtil.getName(User::getNickName));
  }
}

运行结果：