Java 中的 Map List String Object 判空

## 1.Map

可使用工具包有 `CollectionUtils` `MapUtils`

### 返回一个空的`Map`

```java
// 输出1
public static void main(String[] args) {
    HashMap<String, String> stringStringHashMap = new HashMap<>();
    boolean empty = MapUtils.isEmpty(stringStringHashMap);
		System.out.println(empty ? "1" : "0");
}
```

对于`Map`其中的数值为空则需要具体判断

```java
// 输出0
public static void main(String[] args) {
    HashMap<String, String> stringStringHashMap = new HashMap<>();
    stringStringHashMap.put("str",null);
    boolean empty = MapUtils.isEmpty(stringStringHashMap);
    System.out.println(empty ? "1" : "0");
}
```

```java
// 输出0
public static void main(String[] args) {
  	HashMap<String, String> stringStringHashMap = new HashMap<>();
  	stringStringHashMap.put("str", null);
  	boolean empty = MapUtils.isEmpty(stringStringHashMap);
  	String str = stringStringHashMap.get("str");
  	if (!empty && str != null) {
    	System.out.println("0");
  	} else {
    	System.out.println("1");
  	}
}
```

```java
// 输出1
public static void main(String[] args) {
  	HashMap<String, String> stringStringHashMap = new HashMap<>();
  	stringStringHashMap.put("st","");
  	boolean empty = MapUtils.isEmpty(stringStringHashMap);
  	String str = stringStringHashMap.get("str");
  	if (!empty && str != null) {
    	System.out.println("0");
  	} else {
    	System.out.println("1");
  	}
}
```

### 返回一个`Map`为空

```java
// 报空指针
public static void main(String[] args) {
    HashMap<String, String> stringStringHashMap= null;
    boolean empty = CollectionUtils.isEmpty(stringStringHashMap);
    System.out.println(empty ? "1" : "0");
}
```