MapUtils 工具类

MapUtils是 Apache Commons 工具包中常用的工具类，使用是需要依赖对应的lab,对应的maven引用如下：

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-collections4</artifactId>
    <version>4.1</version>
</dependency>

MapUtils 常用操作java.util.Map 和 java.util.SortedMap。

常用方法有：
isNotEmpty ( ) 是否不为空
isEmpty ( ) 是否为空
putAll ( ) 添加所有元素
getString ( ) 获取String类型的值
getObject ( ) 获取Object类型的值
getInteger ( )获取Integer类型的值
get*** ( ) 类似上面的
EMPTY_MAP 获取一个不可修改的空类型Map
unmodifiableMap 获取一个不可以修改的Map（不能新增或删除）
unmodifiableSortedMap 获取一个不可以修改的有序的Map（不能新增或删除）
fixedSizeMap 获取一个固定长度的map
multiValueMap 获取一个多值的map(即一个key可以对应多个value值)
invertMap 返回一个key与value对调的map
predicatedMap() 返回一个满足predicate条件的map
lazyMap 返回一个lazy的map（值在需要的时候可以创建）

String name = MapUtils.getString(map, "name");

int money = MapUtils.getInteger(map,"money");//包装类型自动拆箱

boolean empty = MapUtils.isEmpty(map);

boolean notEmpty = MapUtils.isNotEmpty(map);

//把二维数组转换成map
String[][] user = {{"names","zhangfsan"},{"sexs","1f"}};
Map map1 = MapUtils.putAll(map, user);

public class MapUtilsTest {
    private String[][] color2DArray = new String[][] {
        {"RED", "#FF0000"},
        {"GREEN", "#00FF00"},
        {"BLUE", "#0000FF"}
    };
    private String[] color1DArray = new String[] {
        "RED", "#FF0000",
        "GREEN", "#00FF00",
        "BLUE", "#0000FF"
    };
    private Map<String, String> colorMap;
 
    //...
}

@Test
public void whenCreateMapFrom2DArray_theMapIsCreated() {
    this.colorMap = MapUtils.putAll(
      new HashMap<>(), this.color2DArray);
 
    assertThat(
      this.colorMap, 
      is(aMapWithSize(this.color2DArray.length)));
    
    assertThat(this.colorMap, hasEntry("RED", "#FF0000"));
    assertThat(this.colorMap, hasEntry("GREEN", "#00FF00"));
    assertThat(this.colorMap, hasEntry("BLUE", "#0000FF"));
}

@Test
public void whenCreateMapFrom1DArray_theMapIsCreated() {
    this.colorMap = MapUtils.putAll(
      new HashMap<>(), this.color1DArray);
    
    assertThat(
      this.colorMap, 
      is(aMapWithSize(this.color1DArray.length / 2)));
 
    assertThat(this.colorMap, hasEntry("RED", "#FF0000"));
    assertThat(this.colorMap, hasEntry("GREEN", "#00FF00"));
    assertThat(this.colorMap, hasEntry("BLUE", "#0000FF"));
}

@Test
public void whenVerbosePrintMap_thenMustPrintFormattedMap() {
    MapUtils.verbosePrint(System.out, "Optional Label", this.colorMap);
}

/**
Optional Label = 
{
    RED = #FF0000
    BLUE = #0000FF
    GREEN = #00FF00
}
/*

@Test
public void whenGetKeyNotPresent_thenMustReturnDefaultValue() {
    String defaultColorStr = "COLOR_NOT_FOUND";
    String color = MapUtils
      .getString(this.colorMap, "BLACK", defaultColorStr);
    
    assertEquals(color, defaultColorStr);
}

@Test
public void whenGetOnNullMap_thenMustReturnDefaultValue() {
    String defaultColorStr = "COLOR_NOT_FOUND";
    String color = MapUtils.getString(null, "RED", defaultColorStr);
    
    assertEquals(color, defaultColorStr);
}

@Test
public void whenInvertMap_thenMustReturnInvertedMap() {
    Map<String, String> invColorMap = MapUtils.invertMap(this.colorMap);
 
    int size = invColorMap.size();
    Assertions.assertThat(invColorMap)
      .hasSameSizeAs(colorMap)
      .containsKeys(this.colorMap.values().toArray(new String[] {}))
      .containsValues(this.colorMap.keySet().toArray(new String[] {}));
}

/**
{
    #00FF00 = GREEN
    #FF0000 = RED
    #0000FF = BLUE
}
*/

@Test(expected = IllegalArgumentException.class)
public void whenCreateFixedSizedMapAndAdd_thenMustThrowException() {
    Map<String, String> rgbMap = MapUtils
      .fixedSizeMap(MapUtils.putAll(new HashMap<>(), this.color1DArray));
    
    rgbMap.put("ORANGE", "#FFA500");
}

@Test(expected = IllegalArgumentException.class)
public void whenAddDuplicate_thenThrowException() {
    Map<String, String> uniqValuesMap 
      = MapUtils.predicatedMap(this.colorMap, null, 
        PredicateUtils.uniquePredicate());
    
    uniqValuesMap.put("NEW_RED", "#FF0000");
}

@Test
public void whenCreateLazyMap_theMapIsCreated() {
    Map<Integer, String> intStrMap = MapUtils.lazyMap(
      new HashMap<>(),
      TransformerUtils.stringValueTransformer());
    
    assertThat(intStrMap, is(anEmptyMap()));
    
    intStrMap.get(1);
    intStrMap.get(2);
    intStrMap.get(3);
    
    assertThat(intStrMap, is(aMapWithSize(3)));
}

参考：
https://tool.oschina.net/uploads/apidocs/commons-collections/index.html?org/apache/commons/collections/MapUtils.html
https://www.baeldung.com/apache-commons-map-utils
https://www.programcreek.com/java-api-examples/index.php?api=org.apache.commons.collections.MapUtils
https://www.codota.com/code/java/methods/org.apache.commons.collections.MapUtils/getInteger
https://www.techiedelight.com/initialize-map-using-apache-commons-collections-java/