四大函数式接口

消费型接口

@FunctionalInterface
public interface Consumer {
    void accept(T t);
}

供给型接口

@FunctionalInterface
public interface Supplier {
    T get();
}

断定型接口

@FunctionalInterface
public interface Predicate {
    boolean test(T t);
}

函数型接口

@FunctionalInterface
public interface Function {
    R apply(T t);
}

SerializedLambda

在java 8中，如果函数式接口继承了Serializable，且被lambda表达式实现时，编译后的实现类会有一个私有”writeReplace”方法，该方法返回一个SerializedLambda对象。通过SerializedLambda类，我们可以获得函数式接口及其实现类等各种信息。

@FunctionalInterface
public interface SFunction extends Function, Serializable {
}

import java.lang.invoke.SerializedLambda;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.function.Function;
public class LambdaUtils {
    /**
     * 获取实现lambda函数型接口方法返回的Field，如 User::getName -> name
     */
    public static  Field convertToField(Function column) {
        String entityName = null;
        String methodName = null;
        try {
            Method method = column.getClass().getDeclaredMethod("writeReplace");
            method.setAccessible(true);
            SerializedLambda serializedLambda = (SerializedLambda) method.invoke(column);
            //获取实现方法所在类的全限定名，用"/"连接的字符串
            entityName = serializedLambda.getImplClass().replace("/", ".");
            //获取实现方法的名称
            methodName = serializedLambda.getImplMethodName();
            String fieldName = captureName(methodName);
            return Class.forName(entityName).getDeclaredField(fieldName);
        } catch (ReflectiveOperationException e) {
            throw new RuntimeException(entityName + " method: '" + methodName + "' must be getXxx.");
        }
    }
    /**
     * 获取getter或setter方法的字段名，如 getName -> name
     */
    public static String captureName(String name) {
        if (!name.startsWith("get") && !name.startsWith("set")) {
            throw new IllegalStateException("Error parsing property name '" + name + "'.  Didn't start with 'get' or 'set'.");
        }
        char[] chars = Arrays.copyOfRange(name.toCharArray(), 3, name.length());
        if (chars.length >= 1 && chars[0] >= 65 && chars[0] <= 90) {
            chars[0] += 32;
        }
        return String.valueOf(chars);
    }
}