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Java中使用Comparable和Comparator实现字段排序功能

发布2016-12-23浏览2698次

详情内容

Comparable 简介

Comparable 是排序接口。

若一个类实现了Comparable接口，就意味着“该类支持排序”。  即然实现Comparable接口的类支持排序，假设现在存在“实现Comparable接口的类的对象的List列表(或数组)”，则该List列表(或数组)可以通过 Collections.sort（或 Arrays.sort）进行排序。

此外，“实现Comparable接口的类的对象”可以用作“有序映射(如TreeMap)”中的键或“有序集合(TreeSet)”中的元素，而不需要指定比较器。

Comparable 定义

Comparable 接口仅仅只包括一个函数，它的定义如下：

  1. package java.lang;
  2. import java.util.*;
  3.  
  4. public interface Comparable<T> {
  5.     public int compareTo(T o);
  6. }

说明：
假设我们通过 x.compareTo(y) 来“比较x和y的大小”。若返回“负数”，意味着“x比y小”；返回“零”，意味着“x等于y”；返回“正数”，意味着“x大于y”。

 

 

Comparator 简介

Comparator 是比较器接口。

我们若需要控制某个类的次序，而该类本身不支持排序(即没有实现Comparable接口)；那么，我们可以建立一个“该类的比较器”来进行排序。这个“比较器”只需要实现Comparator接口即可。也就是说，我们可以通过“实现Comparator类来新建一个比较器”，然后通过该比较器对类进行排序。

 

Comparator 定义

Comparator 接口仅仅只包括两个函数，它的定义如下：

  1. package java.util;
  2.  
  3. public interface Comparator<T> {
  4.  
  5.     int compare(T o1, T o2);
  6.  
  7.     boolean equals(Object obj);
  8. }

说明：
(01) 若一个类要实现Comparator接口：它一定要实现compareTo(T o1, T o2) 函数，但可以不实现 equals(Object obj) 函数。

        为什么可以不实现 equals(Object obj) 函数呢？ 因为任何类，默认都是已经实现了equals(Object obj)的。 Java中的一切类都是继承于java.lang.Object，在Object.java中实现了equals(Object obj)函数；所以，其它所有的类也相当于都实现了该函数。

(02) int compare(T o1, T o2) 是“比较o1和o2的大小”。返回“负数”，意味着“o1比o2小”；返回“零”，意味着“o1等于o2”；返回“正数”，意味着“o1大于o2”。


Comparator 和 Comparable 比较

Comparable是排序接口；若一个类实现了Comparable接口，就意味着“该类支持排序”。

而Comparator是比较器；我们若需要控制某个类的次序，可以建立一个“该类的比较器”来进行排序。我们不难发现：Comparable相当于“内部比较器”，而Comparator相当于“外部比较器”。

 

Comparator 和 Comparable 实例讲解

首先我们定义一个实现Comparable的接口的实体类，Person：

  1. package com.boonya.program.compare;
  2.  
  3. /**
  4.  * 可比较排序Person
  5.  * 
  6.  * @package com.boonya.program.compare.ComparablePerson
  7.  * @date 2016年12月23日 下午10:36:10
  8.  * @author pengjunlin
  9.  * @comment
  10.  * @update
  11.  */
  12. public class Person implements Comparable<Person> {
  13.  
  14. 	private long id;
  15. 	private String name;
  16. 	private int age;
  17. 	private String email;
  18. 	private String address;
  19.  
  20. 	public Person(long id, String name, int age, String email,
  21. 			String address) {
  22. 		super();
  23. 		this.id = id;
  24. 		this.name = name;
  25. 		this.age = age;
  26. 		this.email = email;
  27. 		this.address = address;
  28. 	}
  29.  
  30. 	public Person() {
  31. 		super();
  32. 	}
  33.  
  34. 	public long getId() {
  35. 		return id;
  36. 	}
  37.  
  38. 	public void setId(long id) {
  39. 		this.id = id;
  40. 	}
  41.  
  42. 	public String getName() {
  43. 		return name;
  44. 	}
  45.  
  46. 	public void setName(String name) {
  47. 		this.name = name;
  48. 	}
  49.  
  50. 	public int getAge() {
  51. 		return age;
  52. 	}
  53.  
  54. 	public void setAge(int age) {
  55. 		this.age = age;
  56. 	}
  57.  
  58. 	public String getEmail() {
  59. 		return email;
  60. 	}
  61.  
  62. 	public void setEmail(String email) {
  63. 		this.email = email;
  64. 	}
  65.  
  66. 	public String getAddress() {
  67. 		return address;
  68. 	}
  69.  
  70. 	public void setAddress(String address) {
  71. 		this.address = address;
  72. 	}
  73.  
  74. 	@Override
  75. 	public int compareTo(Person o) {
  76. 		if (this == o) {
  77. 			return 0;
  78. 		} else if (o != null && o instanceof Person) {
  79. 			Person u = (Person) o;
  80. 			if (id < u.id) {
  81. 				return -1;
  82. 			}else if(id == u.id){
  83. 				return 0;
  84. 			} else {
  85. 				return 1;
  86. 			}
  87. 		} else {
  88. 			return -1;
  89. 		}
  90. 	}
  91.  
  92. 	@Override
  93. 	public String toString() {
  94. 		return "Person [id=" + id + ", name=" + name + ", age=" + age
  95. 				+ ", email=" + email + ", address=" + address + "]";
  96. 	}
  97. 	
  98. 	
  99.  
  100. }
然后定义一个排序枚举类，SortEnum： 

  1. package com.boonya.program.compare;
  2. /**
  3.  * 排序类型枚举
  4.  * 
  5.  * @package com.boonya.program.compare.SortEnum
  6.  * @date   2016年12月23日  上午10:58:44
  7.  * @author pengjunlin
  8.  * @comment   
  9.  * @update
  10.  */
  11. public enum SortEnum {
  12. 	
  13. 	/**
  14. 	 * 升序
  15. 	 */
  16. 	ASC(0),
  17. 	/**
  18. 	 * 降序
  19. 	 */
  20. 	DESC(1);
  21. 	
  22. 	private int value=0;
  23.  
  24. 	public int getValue() {
  25. 		return value;
  26. 	}
  27.  
  28. 	public void setValue(int value) {
  29. 		this.value = value;
  30. 	}
  31.  
  32. 	private SortEnum(int value) {
  33. 		this.value = value;
  34. 	}
  35. 	
  36. 	
  37.  
  38. }

定义Person的比较器，PersonComparator： 

  1. package com.boonya.program.compare;
  2.  
  3. import java.util.Comparator;
  4. /**
  5.  * 比较器PersonComparator
  6.  * 
  7.  * @package com.boonya.program.compare.PersonComparator
  8.  * @date   2016年12月23日  上午10:56:53
  9.  * @author pengjunlin
  10.  * @comment   
  11.  * @update
  12.  */
  13. public class PersonComparator implements Comparator<Person> {
  14.  
  15. 	private String sortFieldName;
  16.  
  17. 	private SortEnum sortEnum;
  18.  
  19. 	public String getSortFieldName() {
  20. 		return sortFieldName;
  21. 	}
  22.  
  23. 	public void setSortFieldName(String sortFieldName) {
  24. 		this.sortFieldName = sortFieldName;
  25. 	}
  26.  
  27. 	public SortEnum getSortEnum() {
  28. 		return sortEnum;
  29. 	}
  30.  
  31. 	public void setSortEnum(SortEnum sortEnum) {
  32. 		this.sortEnum = sortEnum;
  33. 	}
  34.  
  35. 	public PersonComparator() {
  36. 		super();
  37. 	}
  38.  
  39. 	public PersonComparator(SortEnum sortEnum) {
  40. 		super();
  41. 		this.sortEnum = sortEnum;
  42. 	}
  43.  
  44. 	public PersonComparator(String sortFieldName, SortEnum sortEnum) {
  45. 		super();
  46. 		this.sortFieldName = sortFieldName;
  47. 		this.sortEnum = sortEnum;
  48. 	}
  49.  
  50. 	@Override
  51. 	public int compare(Person o1, Person o2) {
  52. 		if (sortFieldName == null) {
  53. 			if (sortEnum == SortEnum.DESC) {
  54. 				return o2.compareTo(o1);
  55. 			} else {
  56. 				return o1.compareTo(o2);
  57. 			}
  58. 		} else {
  59. 			if (sortEnum == SortEnum.DESC) {
  60. 				if (sortFieldName.equals("id")) {
  61. 					long val = o2.getId() - o1.getId();
  62. 					if (val < 0)
  63. 						return 1;
  64. 					else if (val > 0)
  65. 						return -1;
  66. 					else
  67. 						return 0;
  68. 				} else if (sortFieldName.equals("name")) {
  69. 					return o2.getName().compareTo(o1.getName());
  70. 				} else if (sortFieldName.equals("age")) {
  71. 					int val = o2.getAge() - o1.getAge();
  72. 					if (val < 0)
  73. 						return 1;
  74. 					else if (val > 0)
  75. 						return -1;
  76. 					else
  77. 						return 0;
  78. 				} else if (sortFieldName.equals("email")) {
  79. 					return o2.getEmail().compareTo(o1.getEmail());
  80. 				} else if (sortFieldName.equals("address")) {
  81. 					return o2.getAddress().compareTo(o1.getAddress());
  82. 				}
  83. 				return o2.compareTo(o1);
  84. 			} else {
  85. 				if (sortFieldName.equals("id")) {
  86. 					long val = o1.getId() - o2.getId();
  87. 					if (val > 0)
  88. 						return 1;
  89. 					else if (val < 0)
  90. 						return -1;
  91. 					else
  92. 						return 0;
  93. 				} else if (sortFieldName.equals("name")) {
  94. 					return o1.getName().compareTo(o2.getName());
  95. 				} else if (sortFieldName.equals("age")) {
  96. 					int val = o1.getAge() - o2.getAge();
  97. 					if (val > 0)
  98. 						return 1;
  99. 					else if (val < 0)
  100. 						return -1;
  101. 					else
  102. 						return 0;
  103. 				} else if (sortFieldName.equals("email")) {
  104. 					return o1.getEmail().compareTo(o2.getEmail());
  105. 				} else if (sortFieldName.equals("address")) {
  106. 					return o1.getAddress().compareTo(o2.getAddress());
  107. 				}
  108. 				return o1.compareTo(o2);
  109. 			}
  110.  
  111. 		}
  112.  
  113. 	}
  114.  
  115. }

最后测试一下我们的排序，PersonComparatorTest： 

  1. package com.boonya.program.compare;
  2.  
  3. import java.util.ArrayList;
  4. import java.util.Collections;
  5. import org.junit.Test;
  6. /**
  7.  * 比较器测试
  8.  * 
  9.  * @package com.boonya.program.compare.PersonComparatorTest
  10.  * @date   2016年12月23日  上午10:58:06
  11.  * @author pengjunlin
  12.  * @comment   
  13.  * @update
  14.  */
  15. public class PersonComparatorTest {
  16.  
  17. 	@Test
  18. 	public void sortAscTest() {
  19. 		ArrayList<Person> persons = new ArrayList<Person>();
  20. 		Person p1 = new Person(1, "Allen", 12, "Allen@support.com", "New York");
  21. 		Person p2 = new Person(5, "Bob", 9, "Bob@support.com", "Atlantic");
  22. 		Person p3 = new Person(2, "Author", 20, "Author@support.com", "Washington");
  23. 		Person p4 = new Person(3, "Peter", 30, "Peter@support.com", "Los Angilis");
  24. 		Person p5 = new Person(4, "Mercy", 21, "Mercy@support.com", "San Fransisco");
  25. 		persons.add(p1);
  26. 		persons.add(p2);
  27. 		persons.add(p3);
  28. 		persons.add(p4);
  29. 		persons.add(p5);
  30. 		
  31. 		System.out.println(">>>>========sort by id asc===========<<<<"); 
  32. 		PersonComparator comparator=new PersonComparator(SortEnum.ASC);
  33.  
  34. 		Collections.sort(persons, comparator);// 用我们写好的Comparator对persons进行排序
  35. 		for (int i = 0; i < persons.size(); i++) {
  36. 			System.out.println(persons.get(i).toString());
  37. 		}
  38. 	}
  39. 	
  40. 	@Test
  41. 	public void sortDescTest() {
  42. 		ArrayList<Person> persons = new ArrayList<Person>();
  43. 		Person p1 = new Person(1, "Allen", 12, "Allen@support.com", "New York");
  44. 		Person p2 = new Person(5, "Bob", 9, "Bob@support.com", "Atlantic");
  45. 		Person p3 = new Person(2, "Author", 20, "Author@support.com", "Washington");
  46. 		Person p4 = new Person(3, "Peter", 30, "Peter@support.com", "Los Angilis");
  47. 		Person p5 = new Person(4, "Mercy", 21, "Mercy@support.com", "San Fransisco");
  48. 		persons.add(p1);
  49. 		persons.add(p2);
  50. 		persons.add(p3);
  51. 		persons.add(p4);
  52. 		persons.add(p5);
  53. 		
  54. 		System.out.println(">>>>========sort by id desc===========<<<<"); 
  55. 		PersonComparator comparator=new PersonComparator(SortEnum.DESC);
  56.  
  57. 		Collections.sort(persons, comparator);// 用我们写好的Comparator对persons进行排序
  58. 		for (int i = 0; i < persons.size(); i++) {
  59. 			System.out.println(persons.get(i).toString());
  60. 		}
  61. 	}
  62. 	
  63. 	@Test
  64. 	public void sortByFieldAscTest() {
  65. 		ArrayList<Person> persons = new ArrayList<Person>();
  66. 		Person p1 = new Person(1, "Allen", 12, "Allen@support.com", "New York");
  67. 		Person p2 = new Person(5, "Bob", 9, "Bob@support.com", "Atlantic");
  68. 		Person p3 = new Person(2, "Author", 20, "Author@support.com", "Washington");
  69. 		Person p4 = new Person(3, "Peter", 30, "Peter@support.com", "Los Angilis");
  70. 		Person p5 = new Person(4, "Mercy", 21, "Mercy@support.com", "San Fransisco");
  71. 		persons.add(p1);
  72. 		persons.add(p2);
  73. 		persons.add(p3);
  74. 		persons.add(p4);
  75. 		persons.add(p5);
  76. 		
  77. 		System.out.println(">>>>========sort by name asc===========<<<<"); 
  78. 		PersonComparator comparator=new PersonComparator("name",SortEnum.ASC);
  79.  
  80. 		Collections.sort(persons, comparator);// 用我们写好的Comparator对persons进行排序
  81. 		for (int i = 0; i < persons.size(); i++) {
  82. 			System.out.println(persons.get(i).toString());
  83. 		}
  84. 		
  85. 		System.out.println(">>>>========sort by age asc===========<<<<"); 
  86. 		PersonComparator comparator2=new PersonComparator("age",SortEnum.ASC);
  87.  
  88. 		Collections.sort(persons, comparator2);// 用我们写好的Comparator对persons进行排序
  89. 		for (int i = 0; i < persons.size(); i++) {
  90. 			System.out.println(persons.get(i).toString());
  91. 		}
  92. 		
  93. 		System.out.println(">>>>========sort by email asc===========<<<<"); 
  94. 		PersonComparator comparator3=new PersonComparator("email",SortEnum.ASC);
  95.  
  96. 		Collections.sort(persons, comparator3);// 用我们写好的Comparator对persons进行排序
  97. 		for (int i = 0; i < persons.size(); i++) {
  98. 			System.out.println(persons.get(i).toString());
  99. 		}
  100. 		
  101. 		System.out.println(">>>>========sort by address asc===========<<<<"); 
  102. 		PersonComparator comparator4=new PersonComparator("address",SortEnum.ASC);
  103.  
  104. 		Collections.sort(persons, comparator4);// 用我们写好的Comparator对persons进行排序
  105. 		for (int i = 0; i < persons.size(); i++) {
  106. 			System.out.println(persons.get(i).toString());
  107. 		}
  108. 	}
  109.  
  110. }

输出结果： 

  1. >>>>========sort by id asc===========<<<<
  2. Person [id=1, name=Allen, age=12, email=Allen@support.com, address=New York]
  3. Person [id=2, name=Author, age=20, email=Author@support.com, address=Washington]
  4. Person [id=3, name=Peter, age=30, email=Peter@support.com, address=Los Angilis]
  5. Person [id=4, name=Mercy, age=21, email=Mercy@support.com, address=San Fransisco]
  6. Person [id=5, name=Bob, age=9, email=Bob@support.com, address=Atlantic]
  7. >>>>========sort by id desc===========<<<<
  8. Person [id=5, name=Bob, age=9, email=Bob@support.com, address=Atlantic]
  9. Person [id=4, name=Mercy, age=21, email=Mercy@support.com, address=San Fransisco]
  10. Person [id=3, name=Peter, age=30, email=Peter@support.com, address=Los Angilis]
  11. Person [id=2, name=Author, age=20, email=Author@support.com, address=Washington]
  12. Person [id=1, name=Allen, age=12, email=Allen@support.com, address=New York]
  13. >>>>========sort by name asc===========<<<<
  14. Person [id=1, name=Allen, age=12, email=Allen@support.com, address=New York]
  15. Person [id=2, name=Author, age=20, email=Author@support.com, address=Washington]
  16. Person [id=5, name=Bob, age=9, email=Bob@support.com, address=Atlantic]
  17. Person [id=4, name=Mercy, age=21, email=Mercy@support.com, address=San Fransisco]
  18. Person [id=3, name=Peter, age=30, email=Peter@support.com, address=Los Angilis]
  19. >>>>========sort by age asc===========<<<<
  20. Person [id=5, name=Bob, age=9, email=Bob@support.com, address=Atlantic]
  21. Person [id=1, name=Allen, age=12, email=Allen@support.com, address=New York]
  22. Person [id=2, name=Author, age=20, email=Author@support.com, address=Washington]
  23. Person [id=4, name=Mercy, age=21, email=Mercy@support.com, address=San Fransisco]
  24. Person [id=3, name=Peter, age=30, email=Peter@support.com, address=Los Angilis]
  25. >>>>========sort by email asc===========<<<<
  26. Person [id=1, name=Allen, age=12, email=Allen@support.com, address=New York]
  27. Person [id=2, name=Author, age=20, email=Author@support.com, address=Washington]
  28. Person [id=5, name=Bob, age=9, email=Bob@support.com, address=Atlantic]
  29. Person [id=4, name=Mercy, age=21, email=Mercy@support.com, address=San Fransisco]
  30. Person [id=3, name=Peter, age=30, email=Peter@support.com, address=Los Angilis]
  31. >>>>========sort by address asc===========<<<<
  32. Person [id=5, name=Bob, age=9, email=Bob@support.com, address=Atlantic]
  33. Person [id=3, name=Peter, age=30, email=Peter@support.com, address=Los Angilis]
  34. Person [id=1, name=Allen, age=12, email=Allen@support.com, address=New York]
  35. Person [id=4, name=Mercy, age=21, email=Mercy@support.com, address=San Fransisco]
  36. Person [id=2, name=Author, age=20, email=Author@support.com, address=Washington]

使用反射的方式实现List集合对象任意字段排序

参考：https://github.com/Tony36051/sortByField/blob/master/src/main/java/SortByField.java

  1. package main.java;
  2.  
  3. import java.lang.invoke.MethodHandle;
  4. import java.lang.invoke.MethodHandles;
  5. import java.lang.invoke.MethodType;
  6. import java.lang.reflect.Field;
  7. import java.lang.reflect.InvocationTargetException;
  8. import java.lang.reflect.Method;
  9. import java.util.Collections;
  10. import java.util.Comparator;
  11. import java.util.List;
  12.  
  13. public class SortByField {
  14.  
  15. 	static class Cmp<E> implements Comparator<E> {
  16. 		Method getMethod = null;
  17. 		Field fieldToGet = null;
  18. 		MethodHandle cmpMethodHandle;
  19. 		// Method cmpMethod ;
  20.  
  21. 		Cmp(MethodHandle cmpMethodHandle, /* Method cmpMethod, */Method getMethod) {
  22. 			this.getMethod = getMethod;
  23. 			this.cmpMethodHandle = cmpMethodHandle;
  24. 			// this.cmpMethod = cmpMethod;
  25. 		}
  26.  
  27. 		Cmp(MethodHandle cmpMethodHandle, Field fieldToGet) {
  28. 			this.cmpMethodHandle = cmpMethodHandle;
  29. 			this.fieldToGet = fieldToGet;
  30. 		}
  31.  
  32. 		@Override
  33. 		public int compare(E o1, E o2) {
  34. 			if (o2 == null) {
  35. 				return -1;
  36. 			} else if (o1 == null) {
  37. 				return 1;
  38. 			}
  39. 			try {
  40. 				if (getMethod != null) {
  41. 					return (int) cmpMethodHandle.invokeExact((Comparable<?>) getMethod.invoke(o1),
  42. 							getMethod.invoke(o2));
  43. 					// return (int)cmpMethod.invoke(getMethod.invoke(o1),
  44. 				}
  45. 				if (fieldToGet != null) {
  46. 					return (int) cmpMethodHandle.invokeExact((Comparable<?>) fieldToGet.get(o1), fieldToGet.get(o2));
  47. 				}
  48. 			} catch (IllegalAccessException | IllegalArgumentException | InvocationTargetException e) {
  49. 				System.out.println("If sortByField() isn't modifie, it won't print errorStackTrace. Default return 0");
  50. 				e.printStackTrace();
  51. 			} catch (Throwable e) {
  52. 				e.printStackTrace();
  53. 			}
  54. 			return 0;
  55. 		}
  56. 	}
  57.  
  58. 	/**
  59. 	 * sort a list containing JavaBean according specific key( field ).  
  60. 	 * Mostly, sortByField take ~1.5 times as much as Traditional implementation when list.size() > 100K
  61. 	 * 
  62. 	 * @param list:
  63. 	 *            list to be sorted
  64. 	 * @param fieldName:
  65. 	 *            sort list according this field
  66. 	 * @param order:
  67. 	 *            asc(default) or desc
  68. 	 * @author Tony
  69. 	 * @email 360517703@163.com
  70. 	 * @Time 2015-08-14 11:12
  71. 	 */
  72. 	public static <E> void sortByField(List<E> list, String fieldName, String order) {
  73. 		if (list == null || list.size() < 2) { // no need to sort
  74. 			return;
  75. 		}
  76. 		if (fieldName == null || fieldName.trim().equals(""))
  77. 			return; // won't sort if fieldName is null or ""
  78. 		// get actual class of generic E
  79. 		Class<?> eClazz = null; // use reflect to get the actual class
  80. 		boolean isAllNull = true; // default all elements are null
  81. 		for (E e : list) {
  82. 			if (e != null) {
  83. 				isAllNull = false;
  84. 				eClazz = e.getClass();
  85. 				break;
  86. 			}
  87. 		}
  88. 		if (isAllNull)
  89. 			return; // no need to sort, because all elements are null
  90. 		// check fieldName in Class E
  91. 		Field keyField = null; // the <fieldName> Field as sort key
  92. 		try {
  93. 			keyField = eClazz.getDeclaredField(fieldName);
  94. 		} catch (NoSuchFieldException e1) {
  95. 			e1.printStackTrace();
  96. 			System.out.println("The List<E> doesn't contain fieldName. That is "
  97. 					+ String.format("%s has no Field %s.", eClazz, fieldName));
  98. 		} catch (SecurityException e1) {
  99. 			e1.printStackTrace();
  100. 			System.out.println("deny access to  class or field.");
  101. 		}
  102. 		// check field is either Comparable
  103. 		Class<?> fieldClazz = keyField.getType();
  104. 		boolean isComparable = Comparable.class.isAssignableFrom(fieldClazz);
  105. 		if (isComparable == false)
  106. 			return; // if the class of fieldName is not comparable, don't sort
  107.  
  108. 		// try to use getter method to get field first. Because a little faster
  109. 		// than Field.get(Object)
  110. 		StringBuilder getterName; // adapt to JavaBean getter method
  111. 		if (fieldClazz.getSimpleName().equals("Boolean")) {
  112. 			getterName = new StringBuilder("is");
  113. 		} else {
  114. 			getterName = new StringBuilder("get");
  115. 		}
  116. 		char[] cs = fieldName.toCharArray();
  117. 		if (cs[0] >= 'a' && cs[0] <= 'z')
  118. 			cs[0] -= 32; // change the first char to lowerCase
  119. 		getterName.append(cs);
  120. 		Method getterMethod = null;
  121. 		try {
  122. 			getterMethod = eClazz.getDeclaredMethod(getterName.toString());
  123. 		} catch (NoSuchMethodException | SecurityException e1) {
  124. 			// System.out.println("Field " + fieldName + " has no " + getterName
  125. 			// + "() . ");
  126. 			// e1.printStackTrace();
  127. 		}
  128. 		/*
  129. 		 * // get compare method for specified field. //Abandoned. Because
  130. 		 * MethodHandle.invokeExact() is a little faster than Method.invoke()
  131. 		 * Method cmpMethod = null; try { cmpMethod =
  132. 		 * fieldClazz.getDeclaredMethod("compareTo", fieldClazz); } catch
  133. 		 * (NoSuchMethodException | SecurityException e1) { System.out.println(
  134. 		 * "deny access to class or method(comparaTo).\nImpossible to show errorStrackTrace Because of Comparable check"
  135. 		 * ); e1.printStackTrace(); cmpMethod.setAccessible(true); }
  136. 		 */
  137. 		Cmp<E> cmp;
  138. 		MethodHandles.Lookup lookup = MethodHandles.lookup();
  139. 		MethodType type = MethodType.methodType(int.class, Object.class);
  140. 		MethodHandle mh = null;
  141. 		try {
  142. 			mh = lookup.findVirtual(Comparable.class, "compareTo", type);
  143. 		} catch (NoSuchMethodException | IllegalAccessException e1) {
  144. 			// TODO Auto-generated catch block
  145. 			e1.printStackTrace();
  146. 		}
  147. 		if (getterMethod != null) {
  148. 			// cmpMethod.setAccessible(true);
  149. 			getterMethod.setAccessible(true);
  150. 			cmp = new Cmp<E>(mh, getterMethod);
  151. 		} else { // if cannot find getter method, use reflect to get specified
  152. 					// field
  153. 			keyField.setAccessible(true);
  154. 			cmp = new Cmp<E>(mh, keyField);
  155. 		}
  156.  
  157. 		if (order.equalsIgnoreCase("desc")) {
  158. 			Collections.sort(list, Collections.reverseOrder(cmp));
  159. 			return;
  160. 		}
  161. 		Collections.sort(list, cmp);
  162. 	}
  163.  
  164. 	/**
  165. 	 * sort a list containing JavaBean according specific key( field ) order by
  166. 	 * ascend.  
  167. 	 * 
  168. 	 *  Mostly, sortByField take ~1.5 times as much as Traditional implementation when list.size() > 100K
  169. 	 * @param list
  170. 	 *            list to be sort
  171. 	 * @param fieldName
  172. 	 *            sort list according this field
  173. 	 * @author Tony
  174. 	 * @email 360517703@163.com
  175. 	 * @Time 2015-08-14 11:12
  176. 	 */
  177. 	public static <E> void sortByField(List<E> list, String fieldName) {
  178. 		sortByField(list, fieldName, "asc");
  179. 	}
  180.  
  181. }



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