最近工作中发现对字符串的操作比较多,之前拼接字符串一直使用StringBuilder,后来发现guava提供了Joiner这样的工具,拼接字符串甚至是list,map,String 三者的相互转换的方法也有.下面就是我做的一个整理,请大神不吝指教.

import com.google.common.base.Joiner;
import com.google.common.base.Splitter;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Maps;
import org.junit.Before;
import org.junit.Test;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.StringJoiner;

/**
 * @author yihur
 * @description 测试map, list拼接
 * @date 2019/4/19
 */
public class TestMapAndList {


    private Map<String, String> map;

    private List<Object> list;

    @Before
    public void before_map_new_hashMap() {
        //用guava的方法创建HashMap,这样初始化的时候需要制定HashMap的大小,一般大小指定为:(长度/0.75)+1
        //这样指定大小,创建的好处了以避免HashMap的频繁的扩容导致性能的损耗
        map = Maps.newHashMapWithExpectedSize(6);
        map.put("go", "123");
        map.put("python", "123");
        map.put("java", "123");
        map.put("c++", "123");
        System.out.println(map.toString());
    }

    @Before
    public void before_list_new_arraylist() {
        list = new ArrayList<>();
        list.add(null);
        list.add("陕西省");
        list.add(123456);
        list.add(true);
    }

    @Test
    public void string_joiner_java_test() {
        //StringJoiner一些情况下可以代替StringBuilder
        StringJoiner sj = new StringJoiner("Hollis");
        sj.add("go");
        sj.add("python");
        System.out.println(sj.toString());

        //拼接的时候加上前后的标志位
        StringJoiner stringJoiner = new StringJoiner(":", "[", "]");
        stringJoiner.add("c++").add("go").add("Java").add("python");
        System.out.println(stringJoiner.toString());

        List<String> list = ImmutableList.of("c++", "go", "Java");
        //list拼接字符串,java方法
        String collect = String.join(",", list);
        System.out.println(collect);
        //list拼接字符串,guava方法
        String join = Joiner.on(",").join(list);
        System.out.println(join);
    }

    @Test
    public void test_list_guava_joiner() {

        //忽略Null
        String join = Joiner.on(",").skipNulls().join(list);
        System.out.println(join);
        //用其他值代替null
        String join1 = Joiner.on(",").useForNull("未填写").join(list);
        System.out.println(join1);

        //字符串拼接成list,并忽略空字符串
        String str = "java, , python, go";
        List<String> stringList = Splitter.on(",").omitEmptyStrings().trimResults().splitToList(str);
        System.out.println(stringList);
    }

    @Test
    public void test_map_guava_joiner() {

        //拼接map
        String join = Joiner.on(",").withKeyValueSeparator("=").join(map);
        System.out.println(join);

        //分隔字符串生成map
        String str = "id=123&name=green&age=10";
        Map<String, String> join1 = Splitter.on("&").withKeyValueSeparator("=").split(str);
        System.out.println(join1.toString());
    }
}