java反射快速入门（二）

上一遍博文 , 简单介绍java 反射的常用接口,本遍博文, 我会结合项目开发的实际例子讲解下 java反射的使用

现在有个需求, 要将一个对象转换成xml格式, 或者将一串xml转换一个对象, 这时我们循序渐进, 先从最简单的入手

一： 方案①

场景 ： NBA球员信息描述, 实体类如下

package test.reflect2;import org.dom4j.Element;

public class UserXMLDO {
    
    private Long id;
    private String name;
    private String password;
    private Double height;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public Double getHeight() {
        return height;
    }

    public void setHeight(Double height) {
        this.height = height;
    }
}

现在要把传进来的一个userXMLDO对象转成一串xml 

public static String toStringXML(UserXMLDO userXMLDO) throws Exception {
        StringBuffer sb = new StringBuffer();
        sb.append("");
        sb.append(genNodeXmlString("id", userXMLDO.getId()));
        sb.append(genNodeXmlString("name", userXMLDO.getName()));
        sb.append(genNodeXmlString("password", userXMLDO.getPassword()));
        sb.append(genNodeXmlString("height", userXMLDO.getHeight()));
        sb.append("");
        return sb.toString();
    }
    private static String genNodeXmlString(String nodeName, Object value) {
        StringBuffer sb = new StringBuffer();
        sb.append("<");
        sb.append(nodeName);
        sb.append(">");
        sb.append(value);
        sb.append(");
        sb.append(nodeName);
        sb.append(">");
        return sb.toString();
    }

再提供一个方法,将xml转成userXMLDO对象

public static UserXMLDO toUserXMLDO(String xml) throws Exception {
        UserXMLDO  userXMLDO = new UserXMLDO();
        Element rootElement = DocumentXmlHelper.read(xml).getRootElement();
        
        for(Iterator it = rootElement.elementIterator("id"); it.hasNext();) {
            Element element = (Element) it.next();
            userXMLDO.setId(Long.valueOf(element.getText()));
        }
        
        for(Iterator it = rootElement.elementIterator("name"); it.hasNext();) {
            Element element = (Element) it.next();
            userXMLDO.setName(element.getText());
        }
        
        for(Iterator it = rootElement.elementIterator("password"); it.hasNext();) {
            Element element = (Element) it.next();
            userXMLDO.setPassword(element.getText());
        }
        
        for(Iterator it = rootElement.elementIterator("height"); it.hasNext();) {
            Element element = (Element) it.next();
            userXMLDO.setHeight(Double.valueOf(element.getText()));
        }
        return userXMLDO;
    }

 

上面的方案一,是最容易的想法做法,但此做法显得有点简单粗暴 。比如我要给球员添加一个 体重 属性, 这时你会发现, 要同时修改两个方法

toStringXML()、toUserXMLDO() 的实现

修改如下 ：
　　
private Double weight;

toStringXML() ： sb.append(genNodeXmlString("weight", userXMLDO.getName()));

toUserXMLDO() ：

for(Iterator it = rootElement.elementIterator("weight"); it.hasNext();) { 

　　Element element = (Element) it.next(); 
　　userXMLDO.setHeight(Double.valueOf(element.getText()));
}

添加1个属性,改起来还是可以接受, 添加2个属性,还是可以接受的、....... 再添加100个属性呢？不能接受了吧~

二： 方案② 用反射

添加类型枚举

 1 package test.reflect2;
 2 
 3 import java.util.HashMap;
 4 import java.util.Map;
 5 
 6 public enum NodeEnum {
 7 
 8     userName("name", String.class),
 9     password("password", String.class),
10     userId("id", Long.class),
11     height("height", Double.class),
12     ;
13 
14     NodeEnum(String name, Class type) {
15         this.name = name;
16         this.type = type;
17     }
18 
19     public static Map> getNodeMap() {
20         Map> map = new HashMap>();
21         NodeEnum[] nodeEnums = NodeEnum.values();
22         for (NodeEnum ne : nodeEnums) {
23             map.put(ne.getName(), ne.getType());
24         }
25         return map;
26     }
27 
28     private String name;
29     
30     private Class type;
31 
32     public String getName() {
33         return name;
34     }
35 
36     public void setName(String name) {
37         this.name = name;
38     }
39 
40     public Class getType() {
41         return type;
42     }
43 
44     public void setType(Class type) {
45         this.type = type;
46     }
47 
48 
49 }

View Code

实体类添加 

  1 public class UserXMLDO {
  2 
  3     private static Map> nodeEnumMap = null;
  4     static {
  5         nodeEnumMap = NodeEnum.getNodeMap();
  6     }
  7 
  8     private Long id;
  9     private String name;
 10     private String password;
 11     private Double height;
 12     private Double weight;
 13 
 14     public static String toStringXML(UserXMLDO userXMLDO) throws Exception {
 15         StringBuffer sb = new StringBuffer();
 16         sb.append("");
 17         Iterator>> it = nodeEnumMap.entrySet().iterator();
 18         while (it.hasNext()) {
 19             Entry> entry = it.next();
 20             Object object = userXMLDO.getClass().getDeclaredField(entry.getKey()).get(userXMLDO);
 21             sb.append(genNodeXmlString(entry.getKey(), object == null ? "" : object));
 22         }
 23         sb.append("");
 24         return sb.toString();
 25     }
 26 
 27     public static UserXMLDO toUserXMLDO(String xml) throws Exception {
 28         UserXMLDO userXMLDO = new UserXMLDO();
 29         Element rootElement = DocumentXmlHelper.read(xml).getRootElement();
 30 
 31         Iterator it = rootElement.elementIterator();
 32         while (it.hasNext()) {
 33             Element e = (Element) it.next();
 34             setAttrValue(userXMLDO, e.getName(), e.getTextTrim());
 35         }
 36         return userXMLDO;
 37     }
 38 
 39     private static void setAttrValue(UserXMLDO userXMLDO, String nodeName, String value) throws Exception {
 40 
 41         Field f = userXMLDO.getClass().getDeclaredField(nodeName);
 42         if (nodeEnumMap.get(nodeName).getName().equals(String.class.getName())) {
 43             f.set(userXMLDO, value);
 44         } else if (nodeEnumMap.get(nodeName).getName().equals(Long.class.getName())
 45                 || nodeEnumMap.get(nodeName).getName().equals(Double.class.getName())) {
 46             f.set(userXMLDO,
 47                     nodeEnumMap.get(nodeName).getDeclaredMethod("valueOf", String.class).invoke(userXMLDO, value));
 48         } else {
 49             throw new Exception("仅支持Long, String 类型");
 50         }
 51     }
 52 
 53 
 54     private static String genNodeXmlString(String nodeName, Object value) {
 55         StringBuffer sb = new StringBuffer();
 56         sb.append("<");
 57         sb.append(nodeName);
 58         sb.append(">");
 59         sb.append(value);
 60         sb.append(");
 61         sb.append(nodeName);
 62         sb.append(">");
 63         return sb.toString();
 64     }
 65 
 66     public Long getId() {
 67         return id;
 68     }
 69 
 70     public void setId(Long id) {
 71         this.id = id;
 72     }
 73 
 74     public String getName() {
 75         return name;
 76     }
 77 
 78     public void setName(String name) {
 79         this.name = name;
 80     }
 81 
 82     public String getPassword() {
 83         return password;
 84     }
 85 
 86     public void setPassword(String password) {
 87         this.password = password;
 88     }
 89 
 90     public Double getHeight() {
 91         return height;
 92     }
 93 
 94     public void setHeight(Double height) {
 95         this.height = height;
 96     }
 97 
 98     public Double getWeight() {
 99         return weight;
100     }
101 
102     public void setWeight(Double weight) {
103         this.weight = weight;
104     }
105 }

View Code

 

test ：

 1 public static void main(String[] args) throws Exception {
 2         UserXMLDO userXMLDO = new UserXMLDO();
 3         userXMLDO.setId(1L);
 4         userXMLDO.setName("威少");
 5         userXMLDO.setPassword("三双无解");
 6         userXMLDO.setHeight(1.90d);
 7         userXMLDO.setWeight(85.5d);
 8 
 9         String xml = UserXMLDO.toStringXML(userXMLDO);
10         System.out.println(xml);
11 
12         UserXMLDO userXMLDO2 = UserXMLDO.toUserXMLDO(xml);
13         System.out.println(userXMLDO2);
14     }

View Code

 

方案② , 体现出了很多灵活性, 把 可变 与 不可变 code 抽取出来了, 可能这样说, 或许有点难理解, 我就针对这种做法, 举个例子... 

如 ： 我要球员添加一个 体重 属性, 这是你会发现, 不用去修改

toStringXML()、toUserXMLDO() 的实现

你只要在  NodeEnum 增加一个类型定义即可 : 

weight("weight", Double.class),

素不素改动很小, 如果换一个新人来接手维护, 每次有新的属性需求添加, 他可以很快添加完成, 不需要去改方法的实现, 这样就相对稳定了~~很巧妙做到“以不变应万变”！！

三、总结

相信比较上述两种方案后, 你会觉得反射有时特别好用, 让代码更加健硕, 但是也要记住, 不要一味盲目, 甚至刻意去使用反射, 因为性能差是反射的一大弊端！要权衡评估下。