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