最近写一个题目，要求将一组员工实体类转换成xml文件，或将xml文件转换成一组实体类。题目不难，但写完感觉可以利用泛型和反射将任意一个实体类和xml文件进行转换。于是今天下午立马动手
试了下，做了个简单的模型，可以将简单的实体类和xml文件进行相互转换，但对实体类的属性类型有限制，目前只支持String, Integer, Double三种类型。但是后面可以扩展。
我的大概思路是这样的，只要能拿到实体类的类型信息，我就能拿到实体类的全部字段名称和类型，拼属性的set和get方法更是简单明了，这时候只需要通过方法的反射，将xml文件的数据读取出来给这个反射即可。
反过来只要给我一个任意对象，我就能通过反射拿到该对象所有字段的值，这时候在写xml文件即可。
具体代码如下：
package com.pcq.entity;
import java.io.*;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.DocumentHelper;
import org.dom4j.Element;
import org.dom4j.io.OutputFormat;
import org.dom4j.io.SAXReader;
import org.dom4j.io.XMLWriter;
public class XMLAndEntityUtil {
private static Document document = DocumentHelper.createDocument();
/**
* 判断是否是个xml文件,目前类里尚未使用该方法
* @param filePath
* @return
*/
@SuppressWarnings("unused")
private static boolean isXMLFile(String filePath) {
File file = new File(filePath);
if(!file.exists() || filePath.indexOf(".xml") > -1) {
return false;
}
return true;
}
/**
* 将一组对象数据转换成XML文件
* @param list
* @param filePath 存放的文件路径
*/
public static <T> void writeXML(List<T> list, String filePath) {
Class<?> c = list.get(0).getClass();
String root = c.getSimpleName().toLowerCase() + "s";
Element rootEle = document.addElement(root);
for(Object obj : list) {
try {
Element e = writeXml(rootEle, obj);
document.setRootElement(e);
writeXml(document, filePath);
} catch (NoSuchMethodException | SecurityException
| IllegalAccessException | IllegalArgumentException
| InvocationTargetException e) {
e.printStackTrace();
}
}
}
/**
* 通过一个根节点来写对象的xml节点，这个方法不对外开放，主要给writeXML(List<T> list, String filePath)提供服务
* @param root
* @param object
* @return
* @throws NoSuchMethodException
* @throws SecurityException
* @throws IllegalAccessException
* @throws IllegalArgumentException
* @throws InvocationTargetException
*/
private static Element writeXml(Element root, Object object) throws NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
Class<?> c = object.getClass();
String className = c.getSimpleName().toLowerCase();
Element ele = root.addElement(className);
Field[] fields = c.getDeclaredFields();
for(Field f : fields) {
String fieldName = f.getName();
String param = fieldName.substring(0, 1).toUpperCase() + fieldName.substring(1);
Element fieldElement = ele.addElement(fieldName);
Method m = c.getMethod("get" + param, null);
String s = "";
if(m.invoke(object, null) != null) {
s = m.invoke(object, null).toString();
}
fieldElement.setText(s);
}
return root;
}
/**
* 默认使用utf-8
* @param c
* @param filePath
* @return
* @throws UnsupportedEncodingException
* @throws FileNotFoundException
*/
public static <T> List<T> getEntitys(Class<T> c, String filePath) throws UnsupportedEncodingException, FileNotFoundException {
return getEntitys(c, filePath, "utf-8");
}
/**
* 将一个xml文件转变成实体类
* @param c
* @param filePath
* @return
* @throws FileNotFoundException
* @throws UnsupportedEncodingException
*/
public static <T> List<T> getEntitys(Class<T> c, String filePath, String encoding) throws UnsupportedEncodingException, FileNotFoundException {
File file = new File(filePath);
String labelName = c.getSimpleName().toLowerCase();
SAXReader reader = new SAXReader();
List<T> list = null;
try {
InputStreamReader in = new InputStreamReader(new FileInputStream(file), encoding);
Document document = reader.read(in);
Element root = document.getRootElement();
List elements = root.elements(labelName);
list = new ArrayList<T>();
for(Iterator<Emp> it = elements.iterator(); it.hasNext();) {
Element e = (Element)it.next();
T t = getEntity(c, e);
list.add(t);
}
} catch (DocumentException e) {
e.printStackTrace();
} catch (InstantiationException e1) {
e1.printStackTrace();
} catch (IllegalAccessException e1) {
e1.printStackTrace();
} catch (NoSuchMethodException e1) {
e1.printStackTrace();
} catch (SecurityException e1) {
e1.printStackTrace();
} catch (IllegalArgumentException e1) {
e1.printStackTrace();
} catch (InvocationTargetException e1) {
e1.printStackTrace();
}
return list;
}
/**
* 将一种类型 和对应的 xml元素节点传进来，返回该类型的对象,该方法不对外开放
* @param c 类类型
* @param ele 元素节点
* @return 该类型的对象
* @throws InstantiationException
* @throws IllegalAccessException
* @throws NoSuchMethodException
* @throws SecurityException
* @throws IllegalArgumentException
* @throws InvocationTargetException
*/
@SuppressWarnings("unchecked")
private static <T> T getEntity(Class<T> c, Element ele) throws InstantiationException, IllegalAccessException, NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException {
Field[] fields = c.getDeclaredFields();
Object object = c.newInstance();//
for(Field f : fields) {
String type = f.getType().toString();//获得字段的类型
String fieldName = f.getName();//获得字段名称
String param = fieldName.substring(0, 1).toUpperCase() + fieldName.substring(1);//把字段的第一个字母变成大写
Element e = ele.element(fieldName);
if(type.indexOf("Integer") > -1) {//说明该字段是Integer类型
Integer i = null;
if(e.getTextTrim() != null && !e.getTextTrim().equals("")) {
i = Integer.parseInt(e.getTextTrim());
}
Method m = c.getMethod("set" + param, Integer.class);
m.invoke(object, i);//通过反射给该字段set值
}
if(type.indexOf("Double") > -1) { //说明该字段是Double类型
Double d = null;
if(e.getTextTrim() != null && !e.getTextTrim().equals("")) {
d = Double.parseDouble(e.getTextTrim());
}
Method m = c.getMethod("set" + param, Double.class);
m.invoke(object, d);
}
if(type.indexOf("String") > -1) {//说明该字段是String类型
String s = null;
if(e.getTextTrim() != null && !e.getTextTrim().equals("")) {
s = e.getTextTrim();
}
Method m = c.getMethod("set" + param, String.class);
m.invoke(object, s);
}
}
return (T)object;
}
/**
* 用来写xml文件
* @param doc Document对象
* @param filePath 生成的文件路径
* @param encoding 写xml文件的编码
*/
public static void writeXml(Document doc, String filePath, String encoding) {
XMLWriter writer = null;
OutputFormat format = OutputFormat.createPrettyPrint();
format.setEncoding(encoding);// 指定XML编码
try {
writer = new XMLWriter(new FileWriter(filePath), format);
writer.write(doc);
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
writer.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
/**
* 默认使用utf-8的格式写文件
* @param doc
* @param filePath
*/
public static void writeXml(Document doc, String filePath) {
writeXml(doc, filePath, "utf-8");
}
}
假如有个实体类是：
package com.pcq.entity;
import java.io.Serializable;
public class Emp implements Serializable{
private Integer id;
private String name;
private Integer deptNo;
private Integer age;
private String gender;
private Integer bossId;
private Double salary;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getDeptNo() {
return deptNo;
}
public void setDeptNo(Integer deptNo) {
this.deptNo = deptNo;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public String getGender() {
return gender;
}
public void setGender(String gender) {
this.gender = gender;
}
public Integer getBossId() {
return bossId;
}
public void setBossId(Integer bossId) {
this.bossId = bossId;
}
public Double getSalary() {
return salary;
}
public void setSalary(Double salary) {
this.salary = salary;
}
}
那么写出来的xml文件格式如下：
<?xml version="1.0" encoding="utf-8"?>
<emps>
<emp>
<id>1</id>
<name>张三</name>
<deptNo>50</deptNo>
<age>25</age>
<gender>男</gender>
<bossId>6</bossId>
<salary>9000.0</salary>
</emp>
<emp>
<id>2</id>
<name>李四</name>
<deptNo>50</deptNo>
<age>22</age>
<gender>女</gender>
<bossId>6</bossId>
<salary>8000.0</salary>
</emp>
</emps>
假如有个实体类如下：
package com.pcq.entity;
public class Student {
private Integer id;
private String name;
private Integer age;
private String gender;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public String getGender() {
return gender;
}
public void setGender(String gender) {
this.gender = gender;
}
}
那么写出来的xml文件如下
<?xml version="1.0" encoding="utf-8"?>
<students>
<student>
<id></id>
<name>pcq</name>
<age>18</age>
<gender>男</gender>
</student>
</students>
读取也必须读这种格式的xml文件，才能转换成实体类，要求是实体类的类类型信息（Class）必须要获得到。
另外这里的实体类的属性类型均是Integer,String,Double,可以看到工具类里只对这三种类型做了判断。而且可以预想的是，如果出现一对多的关系，即一个实体类拥有一组另一个类对象的引用，
那xml和实体类的相互转换要比上述的情况复杂的多。lz表示短时间内甚至长时间内也不一定能做的出来，欢迎同道高人指点。