Java：如何根据给定的值映射更新一些POJO字段？

huangapple
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英文:

Java: How to update some of POJO fields according to a given map of values?

问题

以下是翻译好的内容：

我需要根据仅包含更改的映射来更新几个POJO字段。

例如（松散编码）：

  1. 类MyClass{
  3.    public MyClass(a,b,c);
  5.    private int a;
  6.    private int b;
  7.    private int c;
  8. }
  10. int main(){
  11.   Map<String, String> keyValueMap = new HashMap<>();
  12.   
  13.   MyClass obj = new MyClass(1,2,3);
  14.   keyValueMap.put("c", 6);
  15.   keyValueMap.put("b", 4);
  17.   // 仅更新obj的b和c值：
  18.   updateObj(obj, keyValueMap);
  20.   keyValueMap.put("a", 5);
  21.   keyValueMap.put("b", 7);
  23.   // 仅更新obj的a和b值：
  24.   updateObj(obj, keyValueMap);
  25. }
  27. void updateObj(MyClass obj, Map<String, String> keyValueMap){
  29.  for (Map.Entry<String,String> entry : keyValueMap.entrySet())  
  30.       if(entry.getKey().equals("a")
  31.         obj.setA(entry.getValue());
  32.       if(entry.getKey().equals("b")
  33.         obj.setB(entry.getValue());
  34.       if(entry.getKey().equals("c")
  35.         obj.setC(entry.getValue());
  36.   }
  37. }

除了完整的if链外，是否有更好的方法来实现updateObj()吗？

谢谢大家。

英文:

I need to update several POJO fields according to a map which holds only the changes.

For example (loosely coded) :

  1. Class MyClass{
  3.    public MyClass(a,b,c);
  5.    private int a;
  6.    private int b;
  7.    private int c;
  8. }
  10. int main(){
  11.   Map&lt;String, String&gt; keyValueMap = new HashMap&lt;&gt;();
  12.   
  13.   MyClass obj = new MyClass(1,2,3);
  14.   keyValueMap.put(&quot;c&quot;, 6);
  15.   keyValueMap.put(&quot;b&quot;, 4);
  17.   //Update only b and c values of obj:
  18.   updateObj(obj, keyValueMap);
  20.   keyValueMap.put(&quot;a&quot;, 5);
  21.   keyValueMap.put(&quot;b&quot;, 7);
  23.   //Update only a and b values of obj:
  24.   updateObj(obj, keyValueMap);
  25. }
  27. void updateObj(MyClass obj, Map&lt;String, String&gt; keyValueMap){
  29.  for (Map.Entry&lt;String,String&gt; entry : keyValueMap.entrySet())  
  30.       if(entry.getKey().equals(&quot;a&quot;)
  31.         obj.setA(entry.getValue();
  32.       if(entry.getKey().equals(&quot;b&quot;)
  33.         obj.setB(entry.getValue();
  34.       if(entry.getKey().equals(&quot;c&quot;)
  35.         obj.setC(entry.getValue();
  36.   }
  37. }

Is there a better method to implement updateObj() apart of a complete if's chain?

Thank you all.

答案1

得分: 1

  1. 示例代码（更新方法）：
  3.     static void updateObj(MyClass obj, Map<String, Integer> keyValueMap) {
  4.             try {
  5.                 Field declaredField =  null;
  6.                 for(String key : keyValueMap.keySet()) {
  7.                     declaredField = MyClass.class.getDeclaredField(key);
  8.                     boolean accessible = declaredField.isAccessible();
  9.                     declaredField.setAccessible(true);
  10.                     declaredField.set(obj, keyValueMap.get(key));
  11.                     declaredField.setAccessible(accessible);
  12.                 }
  13.             } catch (NoSuchFieldException | IllegalAccessException e) {
  14.                 e.printStackTrace();
  15.             }
  16.     
  17.         }
英文:

Example code (update method):

  1. static void updateObj(MyClass obj, Map&lt;String, Integer&gt; keyValueMap) {
  2.         try {
  3.             Field declaredField =  null;
  4.             for(String key:keyValueMap.keySet()) {
  5.                 declaredField = MyClass.class.getDeclaredField(key);
  6.                 boolean accessible = declaredField.isAccessible();
  7.                 declaredField.setAccessible(true);
  8.                 declaredField.set(obj, keyValueMap.get(key));
  9.                 declaredField.setAccessible(accessible);
  10.             }
  11.         } catch (NoSuchFieldException | IllegalAccessException e) {
  12.             e.printStackTrace();
  13.         }
  15.     }

答案2

得分: 1

你可以使用Java的反射机制来实现你想要做的操作：

  1. static void updateObj(Main obj, Map<String, Integer> keyValueMap){
  2.     try {
  3.         for (Map.Entry<String, Integer> entry : keyValueMap.entrySet()) {
  4.             Field field = Main.class.getField(entry.getKey());
  5.             field.setAccessible(true);
  6.             field.set(obj, entry.getValue());
  7.         }
  8.     } catch (Exception e) {}
  9. }
英文:

You can use Java reflection to do what you want to do:

  1. static void updateObj(Main obj, Map&lt;String, Integer&gt; keyValueMap){
  2.     try {
  3.         for (Map.Entry&lt;String,Integer&gt; entry : keyValueMap.entrySet()) {
  4.             Field field = Main.class.getField(entry.getKey());
  5.             field.setAccessible(true)
  6.             field.set(obj,entry.getValue());
  7.         }
  8.     } catch(Exception e) {}
  9. }

答案3

得分: 0

你可以简单地使用反射API。以下是基于你的代码的示例：

  1. public class Main1 {
  2.     public static void main(String[] args) {
  3.         Map<String, String> keyValueMap = new HashMap<>();
  5.         MyClass obj = new MyClass(1, 2, 3);
  6.         keyValueMap.put("c", "6");
  7.         keyValueMap.put("b", "4");
  9.         System.out.println(obj);
  11.         // 仅更新 obj 的 b 和 c 值：
  12.         updateObj(obj, keyValueMap);
  14.         System.out.println(obj);
  16.         keyValueMap.put("a", "5");
  17.         keyValueMap.put("b", "7");
  19.         // 仅更新 obj 的 a 和 b 值：
  20.         updateObj(obj, keyValueMap);
  22.         System.out.println(obj);
  23.     }
  25.     private static void updateObj(MyClass myClass, Map<String, String> map) {
  26.         Class<MyClass> clazz = MyClass.class;
  27.         for (String fieldName : map.keySet()) {
  28.             try {
  29.                 Field field = clazz.getDeclaredField(fieldName);
  30.                 field.setAccessible(true);
  31.                 field.set(myClass, Integer.parseInt(map.get(fieldName)));
  32.             } catch (NoSuchFieldException ex) {
  33.                 System.out.println("找不到该字段！！！");
  34.             } catch (IllegalAccessException ex) {
  35.                 System.out.println(ex);
  36.             }
  37.         }
  38.     }
  39. }
  41. class MyClass {
  42.     private int a;
  43.     private int b;
  44.     private int c;
  46.     public MyClass(int a, int b, int c) {
  47.         this.a = a;
  48.         this.b = b;
  49.         this.c = c;
  50.     }
  52.     @Override
  53.     public String toString() {
  54.         return "MyClass{" + "a=" + a + ", b=" + b + ", c=" + c + '}';
  55.     }
  56. }

注意：不要忘记为私有成员使用 field.setAccessible(true);，否则会出现 IllegalAccessException。

英文:

You can simply use Reflection API.
Here is an example based on your code:

  1. public class Main1 {
  2. public static void main(String[] args) {
  3. Map&lt;String, String&gt; keyValueMap = new HashMap&lt;&gt;();
  4. MyClass obj = new MyClass(1,2,3);
  5. keyValueMap.put(&quot;c&quot;, &quot;6&quot;);
  6. keyValueMap.put(&quot;b&quot;, &quot;4&quot;);
  7. System.out.println(obj);
  8. //Update only b and c values of obj:
  9. updateObj(obj, keyValueMap);
  10. System.out.println(obj);
  11. keyValueMap.put(&quot;a&quot;, &quot;5&quot;);
  12. keyValueMap.put(&quot;b&quot;, &quot;7&quot;);
  13. //Update only a and b values of obj:
  14. updateObj(obj, keyValueMap);
  15. System.out.println(obj);
  16. }
  17. private static void updateObj(MyClass myClass, Map&lt;String, String&gt; map) {
  18. Class&lt;MyClass&gt; clazz = MyClass.class;
  19. for (String fieldName: map.keySet()) {
  20. try {
  21. Field field = clazz.getDeclaredField(fieldName);
  22. field.setAccessible(true);
  23. field.set(myClass, Integer.parseInt(map.get(fieldName)));
  24. } catch (NoSuchFieldException ex) {
  25. System.out.println(&quot;No Such Field Found!!!&quot;);
  26. } catch (IllegalAccessException ex) {
  27. System.out.println(ex);
  28. }
  29. }
  30. }
  31. }
  32. class MyClass {
  33. private int a;
  34. private int b;
  35. private int c;
  36. public MyClass(int a, int b, int c) {
  37. this.a = a;
  38. this.b = b;
  39. this.c = c;
  40. }
  41. @Override
  42. public String toString() {
  43. return &quot;MyClass{&quot; + &quot;a=&quot; + a + &quot;, b=&quot; + b + &quot;, c=&quot; + c + &#39;}&#39;;
  44. }
  45. }

Note: Do not forget to use field.setAccessible(true); for private members; Otherwise you will get an IllegalAccessException.

huangapple
  • 本文由 发表于 2020年5月5日 14:53:27
  • 转载请务必保留本文链接：https://go.coder-hub.com/61607358.html
  • java
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