Google团队开发的Guava工具包的代码示例

缺乏、安全感 2021-12-11 23:35 195阅读 0赞

## 上一篇 [java代码如何连接Linux虚拟机，还有文件上传下载，等基础命令][java_Linux] ##

## 一、项目源地址 [Github 链 接][Github _] ##

## 二、String 操作 ##

### 2.1 Join ###

示例代码

@Test   // 这个包引的是 org.testng.annotations.Test
    public class JoinerTest {
    
        public void shouldJoinList() {
            final List<String> strings = Lists.newArrayList("first", "second", "third", null, "fifth");
    
            assertEquals("first|second|third|empty|fifth", Joiner.on("|").useForNull("empty").join(strings));
            assertEquals("first|second|third|fifth", Joiner.on("|").skipNulls().join(strings));
        }
        public void shouldJoinMap() {
            final Map<String, String> params = ImmutableMap.of("key1", "value1", "key2", "value2");
            assertEquals("key1=value1&key2=value2", Joiner.on("&").withKeyValueSeparator("=").join(params));
        }
    }

### 2.2 Splitter ###

@Test
    public class SplitterTest {
    
        public void shouldSplitIntoList() {
            final String input = "first,second,third,fourth,,,seventh";
    
            ArrayList<String> strings = Lists.newArrayList("first", "second", "third", "fourth", "", "", "seventh");
    
            ArrayList<String> strings1 = Lists.newArrayList(Splitter.on(",").split(input));
            ArrayList<String> strings2 = Lists.newArrayList(Splitter.on(",").omitEmptyStrings().split(input));
            ArrayList<String> strings3 = Lists.newArrayList(Splitter.on(",").trimResults().split(input));
        }
        public void shouldSplitIntoMap() {
            final String input = "key1=value1&key2=value2";
            ImmutableMap<String, String> of = ImmutableMap.of("key1", "value1", "key2", "value2");
            Map<String, String> split = Splitter.on("&").withKeyValueSeparator("=").split(input);
        }
    }

### 其他 ###

@Test
    public class StringsTest {
    
        private static final String EMPTY = "";
        private static final String NON_EMPTY = "Non-Empty";
    
        public void shouldHandleNulls() {
            // emptyToNull
            assertNull(Strings.emptyToNull(EMPTY));
            assertEquals(NON_EMPTY, Strings.emptyToNull(NON_EMPTY));
    
            // nullToEmpty
            assertEquals(EMPTY, Strings.nullToEmpty(null));
            assertEquals(NON_EMPTY, Strings.nullToEmpty(NON_EMPTY));
    
            // isNullOrEmpty
            assertTrue(Strings.isNullOrEmpty(EMPTY));
            assertTrue(Strings.isNullOrEmpty(null));
            assertFalse(Strings.isNullOrEmpty(NON_EMPTY));
        }
    
        public void shouldCreateStrings() {
            // padStart
            assertEquals("xxxx" + NON_EMPTY, Strings.padStart(NON_EMPTY, 13, 'x'));
            assertEquals(NON_EMPTY, Strings.padStart(NON_EMPTY, 1, 'x'));
    
            // padEnd
            assertEquals(NON_EMPTY + "xxxx", Strings.padEnd(NON_EMPTY, 13, 'x'));
            assertEquals(NON_EMPTY, Strings.padEnd(NON_EMPTY, 1, 'x'));
    
            // repeat
            assertEquals("xyzxyz", Strings.repeat("xyz", 2));
        }
    }

## 三、集合操作 ##

### 3.1 ImmutableCollections 操作 ###

@Test
    public class ImmutableCollectionsTest {
    
    
        // 自动同步，复制
        public void shouldProveUnmodifiableListIsAView() {
            final List<String> baseList = Lists.newArrayList("A", "B", "C");
            final List<String> unmodifiableList = Collections.unmodifiableList(baseList);
    
            assertEquals(3, baseList.size());
            assertEquals(3, unmodifiableList.size());
    
            baseList.add("D");
    
            assertEquals(4, baseList.size());
            assertEquals(4, unmodifiableList.size());
        }
    
        public void shouldProveImmutableListIsADifferentList() {
            final List<String> baseList = Lists.newArrayList("A", "B", "C");
            final List<String> unmodifiableList = ImmutableList.copyOf(baseList);
    
            assertEquals(3, baseList.size());
            assertEquals(3, unmodifiableList.size());
    
            baseList.add("D");
    
            assertEquals(4, baseList.size());
            assertEquals(3, unmodifiableList.size());
        }
    
        public void shouldBuildImmutableList() {
            final List<String> immutableList = ImmutableList.of("A", "B", "C", "D");
    //        immutableList.add("E"); // 不可变集合，强行添加会报错
            assertEquals(4, immutableList.size());
        }
    
        // 这里可实现集合的叠加
        public void shouldBuildImmutableListWithBuilder() {
            final List<String> list1 = Lists.newArrayList("A", "B");
            final List<String> list2 = Lists.newArrayList("C", "D");
            final List<String> list3 = Lists.newArrayList("E", "F");
    
            final List<String> immutableList = ImmutableList.<String>builder()
                    .addAll(list1)
                    .addAll(list2)
                    .addAll(list3)
                    .add("X", "Y", "Z")
                    .build();
            assertEquals(9, immutableList.size());
        }
    
        // 自定义复杂 Map操作
        public void shouldBuildImmutableMultimapWithBuilder() {
            Multimap<String, Integer> immutableMultimap = ImmutableMultimap.<String, Integer>builder()
                    .put("A", 1)
                    .putAll("B", 1, 2, 3, 4)
                    .putAll("C", 10, 15, 20)
                    .build();
    
            assertEquals(1, immutableMultimap.get("A").size());
            assertEquals(4, immutableMultimap.get("B").size());
            assertEquals(3, immutableMultimap.get("C").size());
        }
    }

### 3.2 collection 操作 ###

@Test
    public class Collections2Test {
    
        private Collection<Person> people;
    
        @BeforeMethod
        public void setup() {
            people = Lists.newArrayList(
                    new Person(0, "First", "Person"),
                    new Person(1, "Mary", "Jones"),
                    new Person(2, "Michael", "Parker")
            );
        }
    
        public void shouldFilterCollection() {
            final Collection<Person> filtered = Collections2.filter(people,
                    new Predicate<Person>() {
                        public boolean apply(@Nullable Person input) {
                            return input != null && input.getFirstName().startsWith("M");
                        }
                    });
            filtered.forEach(System.out::println);
    
            assertEquals(2, filtered.size());
        }
    
        public void shouldFilterCollection2() {
            final Collection<Person> filtered = Collections2.filter(people,
                    new Predicate<Person>() {
                        @Override
                        public boolean apply(@org.checkerframework.checker.nullness.qual.Nullable Person input) {
                            return false;
                        }
                    });
            filtered.forEach(System.out::println);
    
            assertEquals(2, filtered.size());
        }
    
        public void shouldTransformCollection() {
            // better to use the collection-specific version on Lists, Maps, Sets, etc.
            final Collection<String> transformed = Collections2.transform(people,
                    input -> input != null ? input.getFirstName() : "");
            transformed.forEach(System.out::println);
        }
    
        public void ImmutableSetUnionTest() {
            Person p1 = new Person(1, "zhang", "san");
            Person p2 = new Person(2, "wang", "wu");
            Person p3 = new Person(3, "li", "qi");
            Person p4 = new Person(4, "zhao", "si");
    
            ImmutableSet<Person> set1 = ImmutableSet.of(p1, p2, p3);
            ImmutableSet<Person> set2= ImmutableSet.of(p2, p4);
            assertEquals(4, Sets.union(set1, set2).size());
    
            assertEquals(ImmutableSet.of(p2), Sets.intersection(set1, set2)); // 取交集
        }
    
    }

### 3.3 Iterables 操作 ###

@Test
    public class IterablesTest {
    
        private List<String> strings = ImmutableList.of("something", "another", "thing", "test");
    
        public void shouldCheckIfAllTrue() {
            final Predicate<String> longerThan5Chars = new Predicate<String>() {
                @Override
                public boolean apply(@Nullable String input) {
                    return input != null && input.length() > 5;
                }
            };
    
            final boolean allLongerThan5Chars = Iterables.all(strings, longerThan5Chars);
            final boolean someLongerThan5Chars = Iterables.any(strings, longerThan5Chars);
    
            assertFalse(allLongerThan5Chars);
            assertTrue(someLongerThan5Chars);
        }
    
        public void shouldReturnFirstItemStartingWithT() {
    
            final String firstItemStartingWithT = Iterables.find(strings, new Predicate<String>() {
                @Override
                public boolean apply(@Nullable String input) {
                    return input != null && input.startsWith("t");
                }
            });
    
            assertEquals("thing", firstItemStartingWithT);
        }
    
        public void shouldReturnDefaultItem() {
    
            final String defaultItem = "hello";
    
            final String result = Iterables.find(strings, new Predicate<String>() {
                @Override
                public boolean apply(@Nullable String input) {
                    return input != null && input.startsWith("X");
                }
            }, defaultItem);
    
            assertEquals(defaultItem, result);
        }
    }

## 四、IO 操作 ##

@Test
    public class IoTest {
        public void messAroundWithFile() {
            File file = new File("d:/woop.txt");
            try {
                Files.touch(file);
                Files.write("Hey sailor!\n hello li", file, Charsets.UTF_8);
                List<String> lines = Files.readLines(file, Charsets.UTF_8);
                lines.forEach(System.out::println);
            } catch (IOException e) {
                Throwables.propagate(e);
            }
        }
    }

## 下一篇，[更多Guava Demo2 示例][Guava Demo2] ##

[java_Linux]: https://blog.csdn.net/qq_42105629/article/details/95055700
[Github _]: https://github.com/google/guava
[Guava Demo2]: https://blog.csdn.net/qq_42105629/article/details/100938981