使用Properties读取配置文件的示例详解

class Properties extends Hashtable<Object,Object>{
    ...
    public Properties() {
        this(null);
    }
    ...
}

Properties properties = new Properties();

//以Reader对象作为参数读取
public synchronized void load(Reader reader) throws IOException {
    load0(new LineReader(reader));
}
​
//以InputStream作为参数读取
public synchronized void load(InputStream inStream) throws IOException {
    load0(new LineReader(inStream));
}

//获取key对应值，如果key不存在，则返回null
public String getProperty(String key) {
    Object oval = super.get(key);
    String sval = (oval instanceof String) ? (String)oval : null;
    return ((sval == null) && (defaults != null)) ? defaults.getProperty(key) : sval;
}
​
//如果不存在key，则返回defaultValue
public String getProperty(String key, String defaultValue) {
    String val = getProperty(key);
    return (val == null) ? defaultValue : val;
}

//设置属性，本质是Hashtable的put方法
public synchronized Object setProperty(String key, String value) {
    return put(key, value);
}
​
//输出为字符流对象Writer
public void store(Writer writer, String comments)
        throws IOException
{
    store0((writer instanceof BufferedWriter)?(BufferedWriter)writer
           : new BufferedWriter(writer),
           comments,
           false);
}
​
//输出为OutputStream流
public void store(OutputStream流 out, String comments)
        throws IOException
{
    store0(new BufferedWriter(new OutputStreamWriter(out, "8859_1")),
           comments,
           true);
}

//类的getResourceAsStream方法，路径加"/"时代表读取resources目录下内容
InputStream inputStream = PropertiesUtils.class.getResourceAsStream方法，路径加"/"时代表读取resources目录下内容("/test.properties");
Properties properties = new Properties();
properties.load(inputStream);
System.out.println(properties.getProperty("test.content"));

//类启动器的getResourceAsStream方法，默认获取路径为src/resources下的文件
InputStream inputStream = PropertiesUtils.class.getClassLoader().getResourceAsStream("test.properties");
Properties properties = new Properties();
properties.load(inputStream);
System.out.println(properties.getProperty("test.content"));

// PropertiesLoaderUtils类的loadAllProperties()方法，读取resources目录
Properties properties = PropertiesLoaderUtils.loadAllProperties("test.properties");
System.out.println(properties.getProperty("test.content"));