在guava库中，自带了过滤器(filter)的功能，可以用来对collection 进行过滤，先看例子： 

import com.google.common.base.Predicates;import com.google.common.collect.Iterables;import com.google.common.collect.Lists;import java.util.List;public class Test {    public static void main(String[] args) {        List
     
       names = Lists.newArrayList("John", "Jane", "Adam", "Tom");        Iterable
      
        result = Iterables.filter(names, Predicates.containsPattern("a"));        // [Jane, Adam]        System.out.println(result);    }}
      
     

在这个例子中，给出一个list，过滤出含有字母a的元素 

此外，可以使用Collections2.filter() 去进行过滤 

import com.google.common.base.Predicates;import com.google.common.collect.Collections2;import com.google.common.collect.Lists;import java.util.Collection;import java.util.List;public class Test {    public static void main(String[] args) {        List
     
       names = Lists.newArrayList("John", "Jane", "Adam", "Tom");        Collection
      
        result = Collections2.filter(names, Predicates.containsPattern("a"));        // [Jane, Adam]        System.out.println(result);    }}
      
     

再来看下predicates判断语言， 

com.google.common.base. Predicate : 根据输入值得到 true 或者 false 

拿Collections2中有2个函数式编程的接口：filter , transform ,例如 ：在Collection<Integer>中过滤大于某数的内容：

import com.google.common.base.Predicate;import com.google.common.collect.Collections2;import com.google.common.collect.Lists;import java.util.Collection;import java.util.List;public class Test {    public static void main(String[] args) {        List
     
       collections = Lists.newArrayList(1, 2, 3, 4);        Collection
      
        filter = Collections2.filter(                collections, new Predicate
       
        () {                    @Override                    public boolean apply(Integer input) {                        return input >= 3;                    }        });        // [3, 4]        System.out.println(filter);    }}
       
      
     

把Lis<Integer>中的Integer类型转换为String , 并添加test作为后缀字符

import com.google.common.base.Function;import com.google.common.collect.Lists;import java.util.List;public class Test {    public static void main(String[] args) {        List
     
       list = Lists.newArrayList(1, 2, 3, 4);        List
      
        transform = Lists.transform(list, new Function
       
        () {            @Override            public String apply(Integer input) {                return input + "_test";            }        });        // [1_test, 2_test, 3_test, 4_test]        System.out.println(transform);    }}
       
      
     

需要说明的是每次调用返回都是新的对象，同时操作过程不是线程安全的。 

将多个prdicate进行组合 

import com.google.common.base.Predicates;import com.google.common.collect.Collections2;import com.google.common.collect.Lists;import java.util.Collection;import java.util.List;public class Test {    public static void main(String[] args) {        List
     
       names = Lists.newArrayList("John", "Jane", "Adam", "Tom");        Collection
      
        result = Collections2.filter(names,                Predicates.or(Predicates.containsPattern("J"),                Predicates.not(Predicates.containsPattern("a"))));        // [John, Jane, Tom]        System.out.println(result);    }}
      
     

上面的例子中找出包含J字母或不包含a的元素; 

再看下如何将集合中的空元素删除： 

import com.google.common.base.Predicates;import com.google.common.collect.Collections2;import com.google.common.collect.Lists;import java.util.Collection;import java.util.List;public class Test {    public static void main(String[] args) {        List
     
       names = Lists.newArrayList("John", null, "Jane", null, "Adam", "Tom");        Collection
      
        result = Collections2.filter(names, Predicates.notNull());        // [John, Jane, Adam, Tom]        System.out.println(result);    }}
      
     

检查一个collection中的所有元素是否符合某个条件： 

import com.google.common.base.Predicates;import com.google.common.collect.Iterables;import com.google.common.collect.Lists;import java.util.List;public class Test {    public static void main(String[] args) {        List
     
       names = Lists.newArrayList("John", "Jane", "Adam", "Tom");        boolean result = Iterables.all(names, Predicates.containsPattern("n|m"));        // true        System.out.println(result);        result = Iterables.all(names, Predicates.containsPattern("a"));        // false        System.out.println(result);    }}