Java8通过Function获取字段名

摘要：Java8通过Function获取字段名。不用再硬编码，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：
字段名：login_name
字段名：nick