Java8通过Function获取字段名（获取实体类的字段名称）

看似很鸡肋其实在某些特殊场景还是比较有用的。
比如你将实体类转Map或者拿到一个Map结果的时候，你是怎么获取某个map的key和value。

方法一：
声明 String key1="name"; key为 key1,value 为map.get(key1);

1         Map<String,Object> map=new HashMap<>();
2         map.put("aaa",1);
3
4         //获取map的key 和value
5         //key 为key1
6         String key1="aaa";
7         //value 为 map.get(key1)
8         map.get(key1);

然后好像日常使用中也没有其他的方法了，下面将带来另外一种使用方法，话不多说直接上代码

  1 import java.io.Serializable;
  2 import java.lang.annotation.ElementType;
  3 import java.lang.annotation.Retention;
  4 import java.lang.annotation.RetentionPolicy;
  5 import java.lang.annotation.Target;
  6 import java.lang.invoke.SerializedLambda;
  7 import java.lang.reflect.Field;
  8 import java.lang.reflect.InvocationTargetException;
  9 import java.lang.reflect.Method;
 10 import java.util.function.Function;
 11
 12 /**
 13  * Java8通过Function函数获取字段名称(获取实体类的字段名称)
 14  * @see ColumnUtil#main(java.lang.String[]) 使用示例
 15  * @author jx
 16  */
 17 public class ColumnUtil {
 18
 19     /**
 20      * 使Function获取序列化能力
 21      */
 22     @FunctionalInterface
 23     public interface SFunction<T, R> extends Function<T, R>, Serializable {
 24     }
 25
 26     /**
 27      * 字段名注解,声明表字段
 28      */
 29     @Target(ElementType.FIELD)
 30     @Retention(RetentionPolicy.RUNTIME)
 31     public @interface TableField {
 32         String value() default "";
 33     }
 34
 35     //默认配置
 36     static String defaultSplit = "";
 37     static Integer defaultToType = 0;
 38
 39     /**
 40      * 获取实体类的字段名称(实体声明的字段名称)
 41      */
 42     public static <T> String getFieldName(SFunction<T, ?> fn) {
 43         return getFieldName(fn, defaultSplit);
 44     }
 45
 46     /**
 47      * 获取实体类的字段名称
 48      * @param split 分隔符，多个字母自定义分隔符
 49      */
 50     public static <T> String getFieldName(SFunction<T, ?> fn, String split) {
 51         return getFieldName(fn, split, defaultToType);
 52     }
 53
 54     /**
 55      * 获取实体类的字段名称
 56      * @param split 分隔符，多个字母自定义分隔符
 57      * @param toType 转换方式，多个字母以大小写方式返回 0.不做转换 1.大写 2.小写
 58      */
 59     public static <T> String getFieldName(SFunction<T, ?> fn, String split, Integer toType) {
 60         SerializedLambda serializedLambda = getSerializedLambda(fn);
 61
 62         // 从lambda信息取出method、field、class等
 63         String fieldName = serializedLambda.getImplMethodName().substring("get".length());
 64         fieldName = fieldName.replaceFirst(fieldName.charAt(0) + "", (fieldName.charAt(0) + "").toLowerCase());
 65         Field field;
 66         try {
 67             field = Class.forName(serializedLambda.getImplClass().replace("/", ".")).getDeclaredField(fieldName);
 68         } catch (ClassNotFoundException | NoSuchFieldException e) {
 69             throw new RuntimeException(e);
 70         }
 71
 72         // 从field取出字段名，可以根据实际情况调整
 73         TableField tableField = field.getAnnotation(TableField.class);
 74         if (tableField != null && tableField.value().length() > 0) {
 75             return tableField.value();
 76         } else {
 77
 78             //0.不做转换 1.大写 2.小写
 79             switch (toType) {
 80                 case 1:
 81                     return fieldName.replaceAll("[A-Z]", split + "$0").toUpperCase();
 82                 case 2:
 83                     return fieldName.replaceAll("[A-Z]", split + "$0").toLowerCase();
 84                 default:
 85                     return fieldName.replaceAll("[A-Z]", split + "$0");
 86             }
 87
 88         }
 89
 90     }
 91
 92     private static <T> SerializedLambda getSerializedLambda(SFunction<T, ?> fn) {
 93         // 从function取出序列化方法
 94         Method writeReplaceMethod;
 95         try {
 96             writeReplaceMethod = fn.getClass().getDeclaredMethod("writeReplace");
 97         } catch (NoSuchMethodException e) {
 98             throw new RuntimeException(e);
 99         }
100
101         // 从序列化方法取出序列化的lambda信息
102         boolean isAccessible = writeReplaceMethod.isAccessible();
103         writeReplaceMethod.setAccessible(true);
104         SerializedLambda serializedLambda;
105         try {
106             serializedLambda = (SerializedLambda) writeReplaceMethod.invoke(fn);
107         } catch (IllegalAccessException | InvocationTargetException e) {
108             throw new RuntimeException(e);
109         }
110         writeReplaceMethod.setAccessible(isAccessible);
111         return serializedLambda;
112     }
113
114
115     /**
116      * 测试用户实体类
117      */
118     public static class TestUserDemo implements Serializable {
119
120         private static final long serialVersionUID = 1L;
121
122         private String loginName;
123         private String name;
124         private String companySimpleName;
125
126         @ColumnUtil.TableField("nick")
127         private String nickName;
128
129         public String getLoginName() {
130             return loginName;
131         }
132
133         public void setLoginName(String loginName) {
134             this.loginName = loginName;
135         }
136
137         public String getNickName() {
138             return nickName;
139         }
140
141         public void setNickName(String nickName) {
142             this.nickName = nickName;
143         }
144
145         public static long getSerialVersionUID() {
146             return serialVersionUID;
147         }
148
149         public String getName() {
150             return name;
151         }
152
153         public void setName(String name) {
154             this.name = name;
155         }
156
157         public String getCompanySimpleName() {
158             return companySimpleName;
159         }
160
161         public void setCompanySimpleName(String companySimpleName) {
162             this.companySimpleName = companySimpleName;
163         }
164     }
165
166
167     /**
168      * 参考示例
169      */
170     public static void main(String[] args) {
171
172         //实体类原字段名称返回
173         System.out.println();
174         System.out.println("实体类原字段名称返回");
175         System.out.println("字段名：" + ColumnUtil.getFieldName(TestUserDemo::getLoginName));
176         System.out.println("字段名：" + ColumnUtil.getFieldName(TestUserDemo::getNickName));
177         System.out.println("字段名：" + ColumnUtil.getFieldName(TestUserDemo::getCompanySimpleName));
178
179         System.out.println();
180         System.out.println("实体类字段名称增加分隔符");
181         System.out.println("字段名：" + ColumnUtil.getFieldName(TestUserDemo::getCompanySimpleName, "_"));
182
183         System.out.println();
184         System.out.println("实体类字段名称增加分隔符 + 大小写");
185         System.out.println("字段名：" + ColumnUtil.getFieldName(TestUserDemo::getCompanySimpleName, "_", 0));
186         System.out.println("字段名：" + ColumnUtil.getFieldName(TestUserDemo::getCompanySimpleName, "_", 1));
187         System.out.println("字段名：" + ColumnUtil.getFieldName(TestUserDemo::getCompanySimpleName, "_", 2));
188
189
190     }
191
192
193 }