Guava学习笔记-基础篇

本篇主要给出Guava基础部分的一些实例：Joiner,Splitters,Strings,Preconditions,Objects,MoreObjects中一些方法的使用，具体的请参考Guava api或源码。

Joiner 主要是集合的一些拼接操作：

public class JoinerDemo {

    List<String> stringList=new ArrayList<String>();

    @Before
    public void init(){
        stringList.add("a");
        stringList.add("b");
        stringList.add("c");
        stringList.add(null);
    }

    //默认情况，遇到null，抛exception
    @Test
    public void defaultJoin(){
        String strDefault = Joiner.on("|").join(stringList);
        System.out.println(strDefault);
    }

    @Test
    public void skipNull(){
        //忽略null
        String str= Joiner.on("|").skipNulls().join(stringList);
        System.out.println(str);
    }

    @Test
    public void useForNull(){
        //不忽略null
        String str2=Joiner.on("|").useForNull("no value").join(stringList);
        System.out.println(str2);
    }

    //joiner 可以使用实现Appendable接口的类
    @Test
    public void join() throws Exception{
        FileWriter fileWriter = new FileWriter("D://log//haha.txt");
        Joiner joiner=Joiner.on("#").useForNull(" ");
        joiner.appendTo(fileWriter,stringList);
        fileWriter.close();
    }

    //用于对map进行连接
    @Test
    public void testMapJoiner(){
        Map<String,String> testMap= Maps.newLinkedHashMap();
        testMap.put("Washington D.C","Redskins");
        testMap.put("New York City","Giants");
        testMap.put("Philadelphia","Eagles");
        testMap.put("Dallas","Cowboys");
        String returnedString=Joiner.on("#").withKeyValueSeparator("=").join(testMap);
        System.out.println(returnedString);
    }
}

Splitter是Joiner的逆向操作：

public class SplitterDemo {
    /**
     * a common task for programmers is to take a string with some delimiter character
     * and plit that string on the delimiter and obtain an array of the parts of the string
     */
    @Test
    public void common(){
        String testString="Monday,Tuesday,Thursday,Friday,,";
        Iterable<String> parts=Splitter.on(",").split(testString);
        for(String s:parts)
            System.out.println(s);
    }

    /**
     * Splitter.trimResults 去掉结果集Iterable每个元素的首尾的空格
     */
    @Test
    public void trimResults(){
        //Just like the Joiner class,Splitter is immutable on creation,
        //so care must be taken to not call the trimResults method after
        //creating the original Splitter class
        Splitter splitter=Splitter.on("|").trimResults();
        Iterable<String> parts=splitter.split("1| 2 | 3 ||");
        for(String s:parts)
            System.out.println(s);
    }

    /**
     * 将指定格式的字符串分割成map
     */
    @Test
    public void testSplitToMap(){
        String testString="Washington D.C=Redskins#New York City=Giants#Philadelphia=Eagles#Dallas=Cowboys";
        Splitter.MapSplitter mapSplitter=Splitter.on("#").withKeyValueSeparator("=");
        Map<String,String> testMap=mapSplitter.split(testString);
        for(String key:testMap.keySet())
            System.out.println(testMap.get(key));

    }
}

Strings 主要是字符串的一些操作等

Charsets 主要是一些常见的编码

CharMatcher 主要是一些简单的正则

public class StringsDemo {
    /**
     * Charsets
     */
    public void testCharsets(){
        byte[] bytes="haha".getBytes(Charsets.UTF_8);
    }

    /**
     * Strings
     static String nullToEmpty(String string) 如果string为null，则返回""
     static String emptyToNull(String string) 如果string为"",返回null
     static boolean isNullOrEmpty(String string) 判断string是否为null或长度是否为0
     static String commonPrefix(CharSequence a, CharSequence b) 返回a,b共同的最长前缀
     static String commonSuffix(CharSequence a, CharSequence b) 返回a,b共同的最长后缀
     static String padEnd(String string, int minLength, char padChar) 使用padChar在尾部将string填充到指定长度minLength
     static String padStart(String string, int minLength, char padChar) 使用padChar在头部将string填充到指定长度minLength
     static String repeat(String string, int count) 将字符串重复N次，返回新字符串
     */
    @Test
    public void testStrings(){
        String res=Strings.padEnd("start",10,'a');
        System.out.println(res);

        res=Strings.repeat("hello",5);
        System.out.println(res);
    }

    @Test
    public void testCharMatcher(){
        //换行使用空格替换
//        CharMatcher.BREAKING_WHITESPACE.replaceFrom(strinfWithlineBreaks," ");
        //多个空字符使用' ' 替换
        String tabsAndSpaces="String with         spaces and        tabs";
        String scrubbed=CharMatcher.WHITESPACE.collapseFrom(tabsAndSpaces,' ');
        System.out.println(scrubbed);

        //去掉首尾空字符，多个空字符使用' ' 替换
        String tabsAndSpaces2="    String with         spaces and        tabs";
        scrubbed=CharMatcher.WHITESPACE.trimAndCollapseFrom(tabsAndSpaces2,' ');
        System.out.println(scrubbed);

        //只保留数字
        String lettersAndNumbers="foo988yxbar12323";
        String retained=CharMatcher.JAVA_DIGIT.retainFrom(lettersAndNumbers);
        System.out.println(retained);

        //匹配多个模式
        String lettersAndOthers="foo988xasfas   dfasd123";
        CharMatcher cm=CharMatcher.JAVA_DIGIT.or(CharMatcher.WHITESPACE);
        retained=cm.retainFrom(lettersAndOthers);
        System.out.println(retained);
    }
}

Objects/MoreObjects

public class User implements Comparable<User>{
    private Integer id;
    private String name;
    private String address;

    public String toString(){
        return MoreObjects.toStringHelper(this).add("id",id).add("name",name).add("address",address).toString();
    }

    public int hashCode(){
        return Objects.hashCode(id,name,address);
    }

    @Override
    public int compareTo(User o) {
        return ComparisonChain.start().compare(this.id,o.id).compare(this.name,o.name).compare(this.address,o.address).result();
    }
}

暂时结束，都是一些入门使用实例，准备在我的下一个项目中引入Guava。

参考资料：《Getting started with Google Guava》