Google-Guava(Utilites)

Posted 2022-06-30 肖帆咪

由 Google 公司开源,Guava是一种基于开源的Java库，Google Guava源于2007年的"Google Collections Library"。这个库是为了方便编码，并减少编码错误。这个库用于提供集合，缓存，支持原语句，并发性，常见注解，字符串处理，I/O和验证的实用方法。

Guava Utilites常用API

• • 1. Joiner
  • 2. Splitter
  • 3. Preconditions
  • 4. Obejects
  • 5. Strings

1. Joiner

String res = Joiner.on("#").join(要拼接的集合);
assertThat(res,equalTo(拼接后的结果));

//跳过NUll拼接
Joiner.on("#"),skipNUlls().join(要拼接的集合);

//碰到null都被替换成别的
Joiner.on("#"),useForNull("Defult").join(要拼接的集合);

//返回的值和要拼接的是同一个对象
StringBuilder resultBuilder = Joiner.on("->").useForNull("*").appendTo(new StringBuilder("E"), stringListWithNullValue);
    

//写入文档中
 private final String targetFileName = "D:\\\\Users\\\\Desktop\\\\guava\\\\guava-test.txt";
   
 try (FileWriter writer = new FileWriter(new File(targetFileName))) 
            Joiner.on("->").useForNull("*").appendTo(writer, stringListWithNullValue);
            assertThat(Files.isFile().test(new File(targetFileName)), equalTo(true));
         catch (IOException e) 
            fail("append to the writer occur fetal error");
        


//stream流 拼接
stringListWithNullValue.stream().filter(item -> item != null && !item.isEmpty()).collect(Collectors.joining("->"));

//stream流拼接使用默认替代null值
stringListWithNullValue.stream()
                .map(item -> item == null || item.isEmpty() ? "*" : item).collect(Collectors.joining("->"));


//拼接map集合
private final Map<String, String> stringMap = ImmutableMap.of("I", "am", "you", "is");
Joiner.on("->").withKeyValueSeparator("=").join(stringMap);


//拼接map集合并写入txt文件
try (FileWriter writer = new FileWriter(new File(targetFileNameToMap))) 
            Joiner.on("->").withKeyValueSeparator("=").appendTo(writer, stringMap);
            assertThat(Files.isFile().test(new File(targetFileNameToMap)), equalTo(true));
 catch (IOException e) 
            fail("append to the writer occur fetal error");
        

2. Splitter

    public void testslitSplit() 
        List<String> result = Splitter.on("|").splitToList("A|B|C");
        assertThat(result, notNullValue());
        assertThat(result.size(), equalTo(3));
        assertThat(result.get(0), equalTo("A"));
        assertThat(result.get(1), equalTo("B"));
        assertThat(result.get(2), equalTo("C"));
    

    public void testsplit_On_Split_OmitEmpty() 
        List<String> result = Splitter.on("|").splitToList("A|B|C||");
        assertThat(result, notNullValue());
        assertThat(result.size(), equalTo(5));

        //忽略空值
        result = Splitter.on("|").omitEmptyStrings().splitToList("A|B|C||");
        assertThat(result.size(), equalTo(3));
    


    public void testsplit_On_Split_OmitEmpty_TrimResult() 
        List<String> result = Splitter.on("|").omitEmptyStrings().splitToList("A | B|C||");
        assertThat(result.size(), equalTo(3));
        assertThat(result.get(0), equalTo("A "));
        assertThat(result.get(1), equalTo(" B"));
        assertThat(result.get(2), equalTo("C"));

        //trimResults()  去掉空格
        result = Splitter.on("|").trimResults().omitEmptyStrings().splitToList("A | B|C||");
        assertThat(result.size(), equalTo(3));
        assertThat(result.get(0), equalTo("A"));
        assertThat(result.get(1), equalTo("B"));
        assertThat(result.get(2), equalTo("C"));
    

    public void testsplitFixLength() 
        List<String> result = Splitter.fixedLength(2).splitToList("aabc");
        assertThat(result, notNullValue());
        assertThat(result.size(), equalTo(2));
        assertThat(result.get(0), equalTo("aa"));
        assertThat(result.get(1), equalTo("bc"));
    


    public void testsplitOnSplitLimit() 
        List<String> result = Splitter.on("#").limit(3).splitToList("A#B#C#D");
        assertThat(result, notNullValue());
        assertThat(result.size(), equalTo(3));
        assertThat(result.get(0), equalTo("A"));
        assertThat(result.get(1), equalTo("B"));
        assertThat(result.get(2), equalTo("C#D"));
    


    public void testsplitOnPatternString() 
        //支持正则表达式分割(传递一个字符串)
        List<String> result = Splitter.onPattern("\\\\|").trimResults().omitEmptyStrings().splitToList("A|B|C||");
        assertThat(result, notNullValue());
        assertThat(result.size(), equalTo(3));
        assertThat(result.get(0), equalTo("A"));
        assertThat(result.get(1), equalTo("B"));
        assertThat(result.get(2), equalTo("C"));
    


    public void testsplitOnPattern() 
        //支持正则表达式分割（传递一个Pattern对象）
        List<String> result = Splitter.on(Pattern.compile("\\\\|")).trimResults().omitEmptyStrings().splitToList("A|B|C||");
        assertThat(result, notNullValue());
        assertThat(result.size(), equalTo(3));
        assertThat(result.get(0), equalTo("A"));
        assertThat(result.get(1), equalTo("B"));
        assertThat(result.get(2), equalTo("C"));
    


    public void testsplitOnSplitToMap() 
        //分割装进Map中withKeyValueSeparator("=")
        Map<String,String> result = Splitter.on(Pattern.compile("\\\\|")).trimResults()
                .omitEmptyStrings().withKeyValueSeparator("=").split("A=a| B=b|C=c||");
        assertThat(result, notNullValue());
        assertThat(result.size(), equalTo(3));
        assertThat(result.get("A"), equalTo("a"));
        assertThat(result.get("B"), equalTo("b"));
        assertThat(result.get("C"), equalTo("c"));
    

3. Preconditions

//检查是否为null
Preconditions.checkNotNull(list);

//检查不为null,并返回message
Preconditions.checkNotNull(list, "The list should not be null");

//返回带数字的message
Preconditions.checkNotNull(list, "The list should not be null and size must be %s", 2);

//判断参数类型
Preconditions.checkArgument();

//判断线程状态  IllegalStateException
Preconditions.checkState();

//判断索引
List<String> list = ImmutebleList.of("张三","李四");
Preconditions.checkElementIndex(10,list.size());

//请求的对象不能为null
Object.requireNonNull(null);

4. Obejects

import com.google.common.base.MoreObjects;
import com.google.common.collect.ComparisonChain;
import java.util.Calendar;

public class ObjectsTest 
    static class Guava implements Comparable<Guava> 
        private final String manufacturer;
        private final String version;
        private final Calendar releaseDate;

        public Guava(String manufacturer, String version, Calendar releaseDate) 
            this.manufacturer = manufacturer;
            this.version = version;
            this.releaseDate = releaseDate;
        

        @Override
        public String toString() 
            return MoreObjects.toStringHelper(this).omitNullValues()
                    .add("manufacturer", this.manufacturer)
                    .add("version", this.version)
                    .add("releaseDate", this.releaseDate).toString();
        

        @Override
        public boolean equals(Object o) 
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            Guava guava = (Guava) o;
            return Objects.equals(this.manufacturer, guava.manufacturer)
                    && Objects.equals(this.version, guava.version)
                    && Objects.equals(this.releaseDate, guava.releaseDate);
        

        @Override
        public int hashCode() 
            return com.google.common.base.Objects.hashCode(manufacturer, version, releaseDate);
        

        @Override
        public int compareTo(Guava o) 
            return ComparisonChain.start().compare(this.manufacturer, o.manufacturer)
                    .compare(this.version, o.version)
                    .compare(this.releaseDate, o.releaseDate).result();
        
    

    public static void main(String[] args) 
        Guava guava1 = new Guava("Google", "23.0", Calendar.Google-Guava(Utilites)

 Service框架浅析Google-Guava Concurrent
 Google Guava - 字符串处理
 Guava Cache 缓存工具使用
 Guava Cache 缓存工具使用
 Google Guava 基本工具