排序是编程中经常要碰到的问题,如果只是一般的数据库数据那么我们完全可以用数据sql语言来排序,但有的时候情况并不是这样,在一些特殊情况下我们不得不自己在java中写一些排序,而通常排序是一件让程序员非常恼火的事情,特别是那些可以让用户自由选择排序规则的情况,想想就头疼.今天正好公司一个组件就碰到了这样的情况,下面我说一下怎么来完成并且实现排序.
首先让我们来看一下用户需求是怎么样(为了更容易理解我将用户需求简化了一下,实际情况可能更复杂), 一个财务人员需要查询公司内所有用户的数据信息,对于查询出来的结果该用户能够自己定义排序规则(例如,他希望对用户姓名进行升序,同时对工资进行降序,并且对生日进行升序,也许有人会说这个直接用sql就能完成,请注意,这个用例是我简化了的,真实的情况会非常复杂,同时并不是一条sql就能解决的).
对于这个需求我们第一个想到的应该有一个员工信息对象(Employee),用户姓名,工资,生日都是这个对象的属性.用户的查询结果就是Employee对象的List.我们知道java本身提供了一个非常好的对于List的排序方法Collections.srot(List <T> list, Comparator c ), 如果我们有一个针对Employee的Comparator对象他知道如何对两个Employee对象进行比较,根据比较结果来决定Employee对象的排列顺序,这样就能够实现用户的需求.第二点,用户能够自己定义一组排序规则,那么我们应该有一个EmployeeSortOrder对象,它包含了所有用户所定义的每一条规则,从需求理解我们可以知道这些规则就是对Employee对象中某些属性定义他的排序规则(升序或者降序),那么我们可以通过引入一个(EmployeeOrder)对象来指明具体Employee对象中有的属性如何来排序,这里需要包括这些属性的类型,应该对于不同的属性比较方式是不一样的.需求分析到这里我们基本就可以得到一个实现排序的模型.
下面我们来看一下具体代码:
Employee对象,一个标准的javabean对象,实际情况可能会是一个更加复杂的对象
/** */ /**
*
*/
package com.demo.sort;
import java.math.BigDecimal;
import java.util.Date;
/** */ /**
* @author Administrator
*
*/
public class Employee ... {
private Long employeeId;
private String firstName;
private String lastName;
private Date birthday;
private BigDecimal payment;
public Date getBirthday() ... {
return birthday;
}
public void setBirthday(Date birthday) ... {
this .birthday = birthday;
}
public Long getEmployeeId() ... {
return employeeId;
}
public void setEmployeeId(Long employeeId) ... {
this .employeeId = employeeId;
}
public String getFirstName() ... {
return firstName;
}
public void setFirstName(String firstName) ... {
this .firstName = firstName;
}
public String getLastName() ... {
return lastName;
}
public void setLastName(String lastName) ... {
this .lastName = lastName;
}
public BigDecimal getPayment() ... {
return payment;
}
public void setPayment(BigDecimal payment) ... {
this .payment = payment;
}
@Override
public int hashCode() ... {
// TODO Auto-generated method stub
return super .hashCode();
}
@Override
public String toString() ... {
StringBuffer buf = new StringBuffer();
buf.append( " [ " );
buf.append( " employeeId= " + employeeId).append( " , " );
buf.append( " firstName= " + firstName).append( " , " );
buf.append( " lastName= " + lastName).append( " , " );
buf.append( " birthday= " + birthday).append( " , " );
buf.append( " payment= " + payment);
buf.append( " ] " );
return buf.toString();
}
}
Employee的complarator对象,他调用了ISortOrder来获得比较结果,这样我们就能够将具体的比较算法留到下层来实现,一旦Employe的比较规则改变,这个类也不需要在理会了.
/** */ /**
*
*/
package com.demo.sort;
import java.util.Comparator;
/** */ /**
* @author Administrator
*
*/
public class EmployeeComparator implements Comparator ... {
ISortOrder sortOrder;
public EmployeeComparator(ISortOrder sortOrder) ... {
this .sortOrder = sortOrder;
}
/**/ /* (non-Javadoc)
* @see java.util.Comparator#compare(java.lang.Object, java.lang.Object)
*/
public int compare(Object arg0, Object arg1) ... {
return sortOrder.compare(arg0,arg1);
}
}
/** */ /**
*
*/
package com.demo.sort;
/** */ /**
* @author Administrator
*
*/
public interface ISortOrder ... {
public int compare(Object arg0, Object arg1);
}
具体的排序规则对象,这个对象记录了Employee对象中具体属性的排序规则和属性类型,如果用户定义了多条规则那么没一条规则就应该对于一个实例.
/** */ /**
*
*/
package com.demo.sort;
/** */ /**
* @author Administrator
*
*/
public class EmployeeOrder ... {
public final static int _LONG = 0 ;
public final static int _STRING = 1 ;
public final static int _DATE = 2 ;
public final static int _BIGDECIMAL = 3 ;
private String propertyName;
private boolean isAsc;
private int dataType;
public EmployeeOrder(String propertyName, boolean isAsc, int dataType) ... {
this .propertyName = propertyName;
this .isAsc = isAsc;
this .dataType = dataType;
}
public boolean isAsc() ... {
return isAsc;
}
public void setAsc( boolean isAsc) ... {
this .isAsc = isAsc;
}
public String getPropertyName() ... {
return propertyName;
}
public void setPropertyName(String propertyName) ... {
this .propertyName = propertyName;
}
public int getDataType() ... {
return dataType;
}
public void setDataType( int dataType) ... {
this .dataType = dataType;
}
}
这里是重点,这个对象知道如何根据order规则来排序,comparator就是调用这个对象的compare方法来获得比较结果,由于 EmployeeOrder对象中定义了对象属性的排序方法,所以这个对象中使用的java的反射来获得具体属性值,并根据不同的属性类型进行比较,如果一共有3条比较规则,那么在比较2个Employee对象是先从第一个规则开始比较,如果比较出来一样,那么在进行第二个规则的比较,否则退出比较.由于本人很懒所以只对其中的一部分属性类型给出了比较方法,并没有实现所有数据类型的比较,大家可以自己实现,呵呵.
/** */ /**
*
*/
package com.demo.sort;
import java.lang.reflect.Field;
import java.math.BigDecimal;
import java.util.List;
/** */ /**
* @author Administrator
*
*/
public class EmployeeSortOrder implements ISortOrder ... {
private List < EmployeeOrder > orders;
public EmployeeSortOrder(List < EmployeeOrder > orders) ... {
this .orders = orders;
}
public int compare(Object arg0, Object arg1) ... {
int result = 0 ;
try ... {
Employee e1 = (Employee) arg0;
Employee e2 = (Employee) arg1;
for (EmployeeOrder order : orders) ... {
Object v1 = getVaule(e1,order.getPropertyName());
Object v2 = getVaule(e2,order.getPropertyName());
result = sort(v1,v2,order.getDataType());
if ( ! order.isAsc()) ... {
result *=- 1 ;
}
if (result != 0 ) ... {
break ;
}
}
} catch (Exception e) ... {
// TODO: handle exception
}
return result;
}
private int sort(Object v1,Object v2, int dataType) ... {
int result = 0 ;
switch (dataType) ... {
case EmployeeOrder._STRING:
String s1 = (String)v1;
String s2 = (String)v2;
result = s1.compareTo(s2);
break ;
case EmployeeOrder._BIGDECIMAL:
BigDecimal d1 = (BigDecimal)v1;
BigDecimal d2 = (BigDecimal)v2;
result = d1.compareTo(d2);
break ;
case EmployeeOrder._LONG:
Long l1 = (Long)v1;
Long l2 = (Long)v2;
result = l1.compareTo(l2);
break ;
default :
result = 0 ;
break ;
}
return result;
}
private Object getVaule(Object obj,String propertyName) ... {
Object result = null ;
try ... {
Class clazz = obj.getClass();
Field field = clazz.getDeclaredField(propertyName);
field.setAccessible( true );
result = field.get(obj);
} catch (Exception e) ... {
e.printStackTrace();
}
return result;
}
}
没多说的,测试类.
package com.demo.sort;
import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.Collections;
import java.util.Date;
import java.util.List;
import junit.framework.TestCase;
public class EmployeeSortTest extends TestCase ... {
private List < Employee > employeeList;
@Override
protected void setUp() throws Exception ... {
super .setUp();
Employee e;
Date date;
Calendar cal = Calendar.getInstance();
employeeList = new ArrayList < Employee > ();
for ( int i = 0 ;i < 10 ;i ++ ) ... {
e = new Employee();
if ( 0 == i % 3 )
cal.add(Calendar.DATE, 1 );
date = cal.getTime();
e.setBirthday(date);
e.setEmployeeId(Long.valueOf(i));
e.setFirstName( " firstName " + i / 2 );
e.setLastName( " LastName " + i * 3 );
e.setPayment( new BigDecimal(i % 3 ));
employeeList.add(e);
}
}
@Override
protected void tearDown() throws Exception ... {
super .tearDown();
}
public void testSort() ... {
List < EmployeeOrder > orders = new ArrayList < EmployeeOrder > ();
EmployeeOrder order = new EmployeeOrder( " firstName " , false ,EmployeeOrder._STRING);
orders.add(order);
order = new EmployeeOrder( " employeeId " , false ,EmployeeOrder._LONG);
orders.add(order);
ISortOrder sortOrder = new EmployeeSortOrder(orders);
EmployeeComparator comparator = new EmployeeComparator(sortOrder);
Collections.sort(employeeList,comparator);
for (Employee employee : employeeList) ... {
System.out.println(employee);
}
}
}