內容

• 是Apache組織下的commons-collections包中的工具類

<dependency>
            <groupId>commons-collections</groupId>
            <artifactId>commons-collections</artifactId>
            <version>3.2.1</version>
        </dependency>

• Map操作相關的，最常用和null值相關

使用

• 取值

public static String getString(final Map map, final Object key) {
        if (map != null) {
            Object answer = map.get(key);
            if (answer != null) {
                return answer.toString();
            }
        }
        return null;
    }
    
public static String getString( Map map, Object key, String defaultValue ) {
        String answer = getString( map, key );
        if ( answer == null ) {
            answer = defaultValue;
        }
        return answer;
    }
 

取值，二元參數無默認字符串；

同樣有針對其他類型的取值方法；

• 賦值

putAll()

public static void safeAddToMap(Map map, Object key, Object value) throws NullPointerException {
        if (value == null) {
            map.put(key, "");
        } else {
            map.put(key, value);
        }
    }

一個是putAll，數組加入map中；

一個是safeAdd，不加入null值；

• 操作

//排序
public static Map orderedMap(Map map) {
        return ListOrderedMap.decorate(map);
    }
 
//反轉，key value互換
public static Map invertMap(Map map) {
        Map out = new HashMap(map.size());
        for (Iterator it = map.entrySet().iterator(); it.hasNext();) {
            Map.Entry entry = (Map.Entry) it.next();
            out.put(entry.getValue(), entry.getKey());
        }
        return out;
    }    
 

@Test
    public void testMapUtils() {
        Map<String,String> map = new HashMap<>();
        map.put("shit","Happens");
        map.put("0","1");
        log.info("{}",MapUtils.getString(map,"shi222t","hhhhh"));
        log.info("order:{}",MapUtils.orderedMap(map));
        log.info("invert:{}",MapUtils.invertMap(map));
    }
    
[INFO ] 2018-10-30 14:07:42,144 method:com.andy.dot.TestAllDots.testMapUtils(TestAllDots.java:177)
hhhhh
[INFO ] 2018-10-30 14:07:42,276 method:com.andy.dot.TestAllDots.testMapUtils(TestAllDots.java:178)
order:{0=1, shit=Happens}
[INFO ] 2018-10-30 14:07:42,277 method:com.andy.dot.TestAllDots.testMapUtils(TestAllDots.java:179)
invert:{Happens=shit, 1=0}

參考文章

• MapUtils常用方法
• Class MapUtils

【技術累積】【點】【java】【29】MapUtils