Google团队开发的Guava工具包的代码示例
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一、项目源地址 Github 链 接
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);
}
}
}
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