java properties.getProperty(key) 方法返回空值
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properties.getProperty(key) method returns null value
提问by kannan arumugam
I am load the properties file and get the value from that file but when i using "Properties"class and getProperty(key)method, it was return nullvalue.
我正在加载属性文件并从该文件中获取值，但是当我使用“属性”类和getProperty(key)方法时，它返回空值。
code:
代码：
public class LoadPropertiesFile {
public static String getProperty (String key, String filePath) {
Properties properties = new Properties();
InputStream inputStream = null;
String value = null;
try {
String appHome = ConfigUtil.getApplicationHome() + filePath;
inputStream = new FileInputStream(appHome);
//load a properties file
properties.load(inputStream);
//get the property value
System.out.println(properties.getProperty("7")); //print **Unlock**
System.err.println(key); //print **7**
System.out.println(value); //print **null**
value = properties.getProperty(key);
} catch (IOException e) {
e.printStackTrace();
} finally {
if (inputStream != null) {
try {
inputStream.close();
} catch(IOException e) {
e.printStackTrace();
}
}
}
return value;
}
}
Output:
输出：
Unlock
7
null
Property File:
属性文件：
2=Interactive
3=Network
4=Batch
5=Service
7=Unlock
8=Network Cleartext
10=Remote Desktop
11=Logon with cached credentials
call method:
调用方法：
logonType = new LoadPropertiesFile().getProperty("7", "path");
When i call that method it will return nullvalue only. please help me guys.
当我调用该方法时，它只会返回空值。请帮帮我伙计们。
回答by flotothemoon
You are initalizing value with null.
您正在使用 null 初始化值。
String value = null;
And you assign it afterprinting it:
并在打印后分配它：
System.out.println(value);
value = properties.getProperty(key);
Output:null
输出：null
So value can only be null when you print it, as you never change its value until System.out.println(value);.
Just switch those two statements:
因此 value 只能在打印时为 null，因为在System.out.println(value);. 只需切换这两个语句：
value = properties.getProperty(key);
System.out.println(value);
Output:unlock
输出：unlock
Edit
编辑
properties.getProperty(key) may return null too, but only if there is no such key in its table, otherwise it will return the assigned value, in your example unlock.
properties.getProperty(key) 也可能返回 null，但前提是它的表中没有这样的键，否则它将返回分配的值，在您的示例中unlock。
See the API Documentation on this for more details:
有关更多详细信息，请参阅 API 文档：
public String getProperty(String key)
Searches for the property with the specified key in this property list. If the key is not found in this property list, the default property list, and its defaults, recursively, are then checked. The method returns null if the property is not found.
公共字符串getProperty（字符串键）
在此属性列表中搜索具有指定键的属性。如果在此属性列表中找不到该键，则递归地检查默认属性列表及其默认值。如果未找到该属性，该方法将返回 null。
http://docs.oracle.com/javase/7/docs/api/java/util/Properties.html#getProperty(java.lang.String)
http://docs.oracle.com/javase/7/docs/api/java/util/Properties.html#getProperty(java.lang.String)
回答by BackSlash
System.out.println(value); //print **null**
value = properties.getProperty(key);
Switch these two lines and initialize valuebeforeprinting it:
切换这两行并value在打印之前进行初始化：
value = properties.getProperty(key);
System.out.println(value); //print Unlock
