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("<UserInfo>");
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("</UserInfo>");
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
package test.reflect2; import java.util.HashMap;
import java.util.Map; public enum NodeEnum { userName("name", String.class),
password("password", String.class),
userId("id", Long.class),
height("height", Double.class),
; NodeEnum(String name, Class<?> type) {
this.name = name;
this.type = type;
} public static Map<String, Class<?>> getNodeMap() {
Map<String, Class<?>> map = new HashMap<String, Class<?>>();
NodeEnum[] nodeEnums = NodeEnum.values();
for (NodeEnum ne : nodeEnums) {
map.put(ne.getName(), ne.getType());
}
return map;
} private String name; private Class<?> type; public String getName() {
return name;
} public void setName(String name) {
this.name = name;
} public Class<?> getType() {
return type;
} public void setType(Class<?> type) {
this.type = type;
} }
实体类添加
public class UserXMLDO {
private static Map<String, Class<?>> nodeEnumMap = null;
static {
nodeEnumMap = NodeEnum.getNodeMap();
}
private Long id;
private String name;
private String password;
private Double height;
private Double weight;
public static String toStringXML(UserXMLDO userXMLDO) throws Exception {
StringBuffer sb = new StringBuffer();
sb.append("<UserInfo>");
Iterator<Entry<String, Class<?>>> it = nodeEnumMap.entrySet().iterator();
while (it.hasNext()) {
Entry<String, Class<?>> entry = it.next();
Object object = userXMLDO.getClass().getDeclaredField(entry.getKey()).get(userXMLDO);
sb.append(genNodeXmlString(entry.getKey(), object == null ? "" : object));
}
sb.append("</UserInfo>");
return sb.toString();
}
public static UserXMLDO toUserXMLDO(String xml) throws Exception {
UserXMLDO userXMLDO = new UserXMLDO();
Element rootElement = DocumentXmlHelper.read(xml).getRootElement();
Iterator<?> it = rootElement.elementIterator();
while (it.hasNext()) {
Element e = (Element) it.next();
setAttrValue(userXMLDO, e.getName(), e.getTextTrim());
}
return userXMLDO;
}
private static void setAttrValue(UserXMLDO userXMLDO, String nodeName, String value) throws Exception {
Field f = userXMLDO.getClass().getDeclaredField(nodeName);
if (nodeEnumMap.get(nodeName).getName().equals(String.class.getName())) {
f.set(userXMLDO, value);
} else if (nodeEnumMap.get(nodeName).getName().equals(Long.class.getName())
|| nodeEnumMap.get(nodeName).getName().equals(Double.class.getName())) {
f.set(userXMLDO,
nodeEnumMap.get(nodeName).getDeclaredMethod("valueOf", String.class).invoke(userXMLDO, value));
} else {
throw new Exception("仅支持Long, String 类型");
}
}
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();
}
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;
}
public Double getWeight() {
return weight;
}
public void setWeight(Double weight) {
this.weight = weight;
}
}
test ：
public static void main(String[] args) throws Exception {
UserXMLDO userXMLDO = new UserXMLDO();
userXMLDO.setId(1L);
userXMLDO.setName("威少");
userXMLDO.setPassword("三双无解");
userXMLDO.setHeight(1.90d);
userXMLDO.setWeight(85.5d);
String xml = UserXMLDO.toStringXML(userXMLDO);
System.out.println(xml);
UserXMLDO userXMLDO2 = UserXMLDO.toUserXMLDO(xml);
System.out.println(userXMLDO2);
}
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。