Guava学习笔记（二）：基础（Joiner，Objects，Splitter及Strings）

添加Maven依赖

JoinerTest

import com.google.common.base.Joiner;
import org.junit.Assert;
import org.junit.Test;

import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;

public class JoinerTest {

    private static final List<String> stringList = new ArrayList<String>();

    static {
        stringList.add("a");
        stringList.add("b");
    }

    /**
     * 基本用法
     *
     * @see Joiner#join(Object[])
     * @see Joiner#join(Iterable)
     * @see Joiner#join(Object, Object, Object...)
     */
    @Test
    public void test_base() {
        String join = Joiner.on("|").join(new String[]{"a", "b"});
        Assert.assertEquals("a|b", join);

        join = Joiner.on("@").join(stringList);
        Assert.assertEquals("a@b", join);

        join = Joiner.on(",").join("a", "b");
        Assert.assertEquals("a,b", join);
    }

    /**
     * 处理有null的情况，跳过或赋予默认值
     */
    @Test
    public void test_null() {
        stringList.add(null);
        String join = Joiner.on("|").skipNulls().join(stringList);
        Assert.assertEquals("a|b", join);

        join = Joiner.on("|").useForNull("no value").join(stringList);
        Assert.assertEquals("a|b|no value", join);
    }

    /**
     * 处理追加情況
     */
    @Test
    public void test_append() {
        StringBuilder stringBuilder = new StringBuilder("test:{");
        String string = Joiner.on("|").appendTo(stringBuilder, stringList).append("}").toString();
        Assert.assertEquals("test:{a|b}", string);
    }

    @Test
    public void test_mapJoiner() {
        Joiner.MapJoiner mapJoiner = Joiner.on(",").withKeyValueSeparator("=");
        LinkedHashMap<Object, Object> linkedHashMap = new LinkedHashMap<Object, Object>();
        linkedHashMap.put("a", 65);
        linkedHashMap.put("b", 66);
        String join = mapJoiner.join(linkedHashMap);
        Assert.assertEquals("a=65,b=66", join);
    }

}

ObjectsTest

import com.google.common.base.MoreObjects;
import com.google.common.base.Objects;
import com.google.common.collect.ComparisonChain;
import org.hamcrest.core.Is;
import org.junit.Assert;
import org.junit.Test;

import java.util.Arrays;
import java.util.Date;
import java.util.List;

public class ObjectsTest {

    private String a;
    private List<Integer> b;
    private Date date;

    @Test
    public void test_compareTo() {
        ObjectsTest objectsTest = new ObjectsTest();
        objectsTest.setA("a");
        ObjectsTest otherObjectsTest = new ObjectsTest();
        otherObjectsTest.setA("b");
        Assert.assertNotEquals(0, objectsTest.compareTo(otherObjectsTest));
    }

    @Test
    public void test_toString() {
        b = Arrays.asList(1, 3);
        String string = MoreObjects.toStringHelper(this).omitNullValues().add("a", a).add("b", b).toString();
        Assert.assertThat(string, Is.is("ObjectsTest{b=[1, 3]}"));
        a = "hah";
        string = MoreObjects.toStringHelper(this).omitNullValues().add("a", a).add("b", b).toString();
        Assert.assertThat(string, Is.is("ObjectsTest{a=hah, b=[1, 3]}"));
    }

    @Test
    public void test_firstNonNull() {
        String s = null;
        String default_value = MoreObjects.firstNonNull(s, "default value");
        Assert.assertEquals("default value", default_value);
    }

    @Test
    public void test_hashCode() {
        int i = Objects.hashCode(a, b);
        Assert.assertNotEquals(0, i);
    }

    public String getA() {
        return a;
    }

    public void setA(String a) {
        this.a = a;
    }

    public List<Integer> getB() {
        return b;
    }

    public void setB(List<Integer> b) {
        this.b = b;
    }

    public int compareTo(ObjectsTest objectsTest) {
        return ComparisonChain.start().compare(this.a, objectsTest.a).compare(this.date, objectsTest.date).result();
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }

}

SplitterTest

import com.google.common.base.Splitter;
import org.junit.Assert;
import org.junit.Test;

import java.util.LinkedHashMap;
import java.util.Map;

import static org.hamcrest.core.Is.is;
import static org.junit.Assert.assertThat;

public class SplitterTest {
    @Test
    public void test_base() {
        Iterable<String> split = Splitter.on("|").split("a|b|c");
        String next = split.iterator().next();
        Assert.assertEquals("a", next);
    }

    @Test
    public void test_mapSplitter() {
        LinkedHashMap<String, String> linkedHashMap = new LinkedHashMap<>();

        linkedHashMap.put("a", "65");
        linkedHashMap.put("b", "66");

        Map<String, String> stringMap = Splitter.on(",").withKeyValueSeparator("=").split("a=65,b=66");
        assertThat(linkedHashMap, is(stringMap));
    }
}

StringsTest

import com.google.common.base.CharMatcher;
import org.junit.Test;

import static org.hamcrest.core.Is.is;
import static org.junit.Assert.assertThat;

public class StringsTest {

    /**
     * 返回输入字符序列的字符串副本，每个匹配此匹配器的连续字符组由单个替换字符替换。 例如：
     * CharMatcher.anyOf(“eko”).collapseFrom(“bookkeeper”，“ - ”) 返回“b-p-r”。
     * 默认实现使用indexIn（CharSequence）来查找第一个匹配字符，然后迭代序列的其余部分，为每个字符调用matches（char）。
     */
    @Test
    public void test_RemoveWhiteSpace() {
        String tabsAndSpaces = "String with spaces and   tabs  ";
        String expected = "String with spaces and tabs ";
        String scrubbed = CharMatcher.WHITESPACE.
                collapseFrom(tabsAndSpaces, ' ');
        assertThat(scrubbed, is(expected));
    }

    /**
     * 除了替换连续字符外，将原字符串中的前后空格去掉
     */
    @Test
    public void test_TrimRemoveWhiteSpace() {
        String tabsAndSpaces = " String with spaces and        tabs             ";
        String expected = "String with spaces and tabs";
        String scrubbed = CharMatcher.WHITESPACE.
                trimAndCollapseFrom(tabsAndSpaces, ' ');
        assertThat(scrubbed, is(expected));
    }

    /**
     * 保留数字,另外CharMatcher还有逻辑运算
     *
     * @see CharMatcher#or(CharMatcher)
     * @see CharMatcher#and(CharMatcher)
     */
    @Test
    public void testRetainFrom() {
        String lettersAndNumbers = "foo989yxbar234";
        String expected = "989234";
        String retained = CharMatcher.JAVA_DIGIT.
                retainFrom(lettersAndNumbers);
        assertThat(expected, is(retained));
    }

}