Predicate 的使用 （主要用于数据的逻辑判断）
唯一性判断：当插入相同的数据时，则报错
非空判断： 当插入的数据为空时，则报错
Predicate notNullPredicate = NotNullPredicate.notNullPredicate();
相等判断：判断值是否相同
自定义判断：（重写函数）实现自定义的逻辑
//自定义谓词
Predicate<String> selfPredicate = new Predicate<String>() {
public boolean evaluate(String s) {
return (s.length() > );
}
};
package cn.others;
import org.apache.commons.collections4.Predicate;
import org.apache.commons.collections4.PredicateUtils;
import org.apache.commons.collections4.functors.EqualPredicate;
import org.apache.commons.collections4.functors.NotNullPredicate;
import org.apache.commons.collections4.functors.UniquePredicate;
import org.apache.commons.collections4.list.PredicatedList;
import java.util.ArrayList;
import java.util.List;
/**
* @author Duoduo
* @version 1.0
* @date 2017/4/15 12:31
*/
public class Test1 {
public static void main(String[] args) {
//自定义谓词
Predicate<String> selfPredicate = new Predicate<String>() {
public boolean evaluate(String s) {
return (s.length() > );
}
};
Predicate notNullPredicate = NotNullPredicate.notNullPredicate();
Predicate allPredicate = PredicateUtils.allPredicate(selfPredicate, notNullPredicate);
List<String> list = PredicatedList.predicatedList(new ArrayList<String>(), allPredicate);
list.add(null);
list.add("1212");
}
public static void uniquePredicate() {
System.out.println("************** 唯一判断 ***************");
Predicate uniquePredicate = UniquePredicate.uniquePredicate();
List<String> list = PredicatedList.predicatedList(new ArrayList<String>(), uniquePredicate);
list.add("1");
list.add("1");
}
public static void equalPredicate() {
System.out.println("************** 相等判断 ***************");
Predicate predicate = EqualPredicate.equalPredicate("Test");
System.out.println(predicate.evaluate("Test1111111"));
}
public static void notNullPredicate() {
System.out.println("************** 非空判断 ***************");
Predicate notNullPredicate = NotNullPredicate.notNullPredicate();
List<String> list = PredicatedList.predicatedList(new ArrayList<String>(), notNullPredicate);
list.add("11111");
list.add(null);
}
}
Transformer 类型转化函数（例如：日期格式化）
package cn.others;
import org.apache.commons.collections4.CollectionUtils;
import org.apache.commons.collections4.Transformer;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
/**
* @author Duoduo
* @version 1.0
* @date 2017/4/15 13:00
*/
public class Test2 {
public static void main(String[] args) {
System.out.println("内置类型转化， 日期格式化输出");
Transformer<Long, String> transformer = new Transformer<Long, String>() {
public String transform(Long aLong) {
return new SimpleDateFormat("yyyy-MM-dd").format(aLong);
}
};
List<Long> list = new ArrayList<Long>();
list.add(L);
list.add(L);
Collection<String> collections = CollectionUtils.collect(list, transformer);
System.out.println(list);
for (String string:collections){
System.out.println(string);
}
}
}
运行结果如下：
内置类型转化， 日期格式化输出 [1000000000, 2000000000] 1970-01-12 1970-01-24
Predicate 和 Transformer 的结合使用（主要用于业务的转化）
需求：当收入 < 1000 时，输出 卖身中。。。
当收入 >= 1000 时，输出 养身中。。。
实现思路：
1. 利用Predicate来进行数据判断大小
2. 利用Transformer来完成类型的转化
优势：完成业务判断和数据的处理的解耦
定义Employee类
package cn.others;
/**
* @author Duoduo
* @version 1.0
* @date 2017/4/15 13:08
*/
public class Employee {
private String name;
private double salary;
public Employee(String name, double salary) {
this.name = name;
this.salary = salary;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
@Override
public String toString() {
return "Employee{" +
"name='" + name + '\'' +
", salary=" + salary +
'}';
}
}
定义Level类
package cn.others;
/**
* @author Duoduo
* @version 1.0
* @date 2017/4/15 13:09
*/
public class Level {
private String name;
private String level;
public Level(String name, String level) {
this.name = name;
this.level = level;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getLevel() {
return level;
}
public void setLevel(String level) {
this.level = level;
}
@Override
public String toString() {
return "Level{" +
"name='" + name + '\'' +
", level='" + level + '\'' +
'}';
}
}
程序处理部分
package cn.others;
import org.apache.commons.collections4.CollectionUtils;
import org.apache.commons.collections4.Predicate;
import org.apache.commons.collections4.Transformer;
import org.apache.commons.collections4.functors.SwitchTransformer;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
/**
* 解耦，处理数据和判断数据分离
* 实现思路：
* 1.定义两个Predicate，一个为 <1000 一个为 >=1000
* 2.定义两个Transformer，一个为 <1000 时需要转义的处理， 一个为 >=1000 时需要转义的处理
* 3.利用 SwitchTransformer 把 Predicate 和 Transformer 关联起来（特别需要注意顺序）
* @author Duoduo
* @version 1.0
* @date 2017/4/15 13:12
*/
public class Test3 {
public static void main(String[] args){
//定义判断谓词
Predicate<Employee> lowSalaryPre = new Predicate<Employee>() {
public boolean evaluate(Employee employee) {
return employee.getSalary()<;
}
};
Predicate<Employee> highSalaryPre = new Predicate<Employee>() {
public boolean evaluate(Employee employee) {
return employee.getSalary()>=;
}
};
//定义转换器
Transformer<Employee, Level> lowTrans = new Transformer<Employee, Level>() {
public Level transform(Employee employee) {
return new Level(employee.getName(), "卖身中。。。。。");
}
};
Transformer<Employee, Level> highTrans = new Transformer<Employee, Level>() {
public Level transform(Employee employee) {
return new Level(employee.getName(), "养身中。。。。。");
}
};
Predicate[] allPre = {lowSalaryPre, highSalaryPre};
Transformer[] allTrans = {lowTrans, highTrans};
//把转化器和判断谓词进行关联
Transformer switchTrans = new SwitchTransformer(allPre, allTrans, null);
List<Employee> list = new ArrayList<Employee>();
list.add(new Employee("test1",));
list.add(new Employee("test2",));
//记性转化
Collection<Level> collections = CollectionUtils.collect(list, switchTrans);
for (Level level : collections){
System.out.println(level);
}
}
}
运行结果
Level{name=’test1’, level=’卖身中。。。。。’}
Level{name=’test2’, level=’养身中。。。。。’}
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