1.Properties類與Properties配置檔案
Properties類繼承自Hashtable類并且實作了Map接口，使用鍵值對的形式來儲存屬性集。不過Properties的鍵和值都是字元串類型。
2.Properties中的主要方法
(1)load(InputStream inStream)
此方法可以從.properties屬性檔案對應的檔案輸入流中，加載屬性清單到Properties類對象。用于讀取Properties配置檔案。Properties prop = new Properties();
//讀取屬性檔案a.properties
InputStream in = new BufferedInputStream (new FileInputStream("a.properties"));
prop.load(in); ///加載屬性清單
Iterator it=prop.stringPropertyNames().iterator();
while(it.hasNext()){
String key=it.next();
System.out.println(key+":"+prop.getProperty(key));
}
in.close();
(2)store(OutputStream out, String comments)
此方法将Properties類對象的屬性清單儲存到輸出流中。用于寫Properties配置檔案。Properties prop = new Properties();
//儲存屬性到b.properties檔案
FileOutputStream oFile = new FileOutputStream("b.properties", true);//true表示追加打開
prop.setProperty("phone", "10086");
prop.store(oFile, "Comment");//如果comments不為空，儲存後的屬性檔案第一行會是#comments,表示注釋資訊；如果為空則沒有注釋資訊。注釋資訊後面是屬性檔案的目前儲存時間資訊。
oFile.close();
(3)getProperty/setProperty
這兩個方法是分别是擷取和設定屬性資訊。
3.示例
下面是黃勇老師寫的擷取屬性檔案的工具類。
public final class PropsUtil {
private static final Logger LOGGER = LoggerFactory.getLogger(PropsUtil.class);
public static Properties loadProps(String fileName) {
Properties props = null;
InputStream is = null;
try {
is = Thread.currentThread().getContextClassLoader().getResourceAsStream(fileName);
if (is == null) {
throw new FileNotFoundException(fileName + " file is not found");
}
props = new Properties();
props.load(is);
} catch (IOException e) {
LOGGER.error("load properties file failure", e);
} finally {
if (is != null) {
try {
is.close();
} catch (IOException e) {
LOGGER.error("close input stream failure", e);
}
}
}
return props;
}
public static String getString(Properties props, String key) {
return getString(props, key, "");
}
public static String getString(Properties props, String key, String defaultValue) {
String value = defaultValue;
if (props.containsKey(key)) {
value = props.getProperty(key);
}
return value;
}
public static int getInt(Properties props, String key) {
return getInt(props, key, 0);
}
// 擷取數值型屬性(可指定預設值)
public static int getInt(Properties props, String key, int defaultValue) {
int value = defaultValue;
if (props.containsKey(key)) {
value = CastUtil.castInt(props.getProperty(key));
}
return value;
}
public static boolean getBoolean(Properties props, String key) {
return getBoolean(props, key, false);
}
public static boolean getBoolean(Properties props, String key, boolean defaultValue) {
boolean value = defaultValue;
if (props.containsKey(key)) {
value = CastUtil.castBoolean(props.getProperty(key));
}
return value;
}
}
裡面用到了CastUtil類，該類是為了處理一些資料轉型操作而準備的，代碼如下：
public final class CastUtil {
public static String castString(Object obj) {
return CastUtil.castString(obj, "");
}
public static String castString(Object obj, String defaultValue) {
return obj != null ? String.valueOf(obj) : defaultValue;
}
public static double castDouble(Object obj) {
return CastUtil.castDouble(obj, 0);
}
public static double castDouble(Object obj, double defaultValue) {
double doubleValue = defaultValue;
if (obj != null) {
String strValue = castString(obj);
if (StringUtil.isNotEmpty(strValue)) {
try {
doubleValue = Double.parseDouble(strValue);
} catch (NumberFormatException e) {
doubleValue = defaultValue;
}
}
}
return doubleValue;
}
public static long castLong(Object obj) {
return CastUtil.castLong(obj, 0);
}
public static long castLong(Object obj, long defaultValue) {
long longValue = defaultValue;
if (obj != null) {
String strValue = castString(obj);
if (StringUtil.isNotEmpty(strValue)) {
try {
longValue = Long.parseLong(strValue);
} catch (NumberFormatException e) {
longValue = defaultValue;
}
}
}
return longValue;
}
public static int castInt(Object obj) {
return CastUtil.castInt(obj, 0);
}
public static int castInt(Object obj, int defaultValue) {
int intValue = defaultValue;
if (obj != null) {
String strValue = castString(obj);
if (StringUtil.isNotEmpty(strValue)) {
try {
intValue = Integer.parseInt(strValue);
} catch (NumberFormatException e) {
intValue = defaultValue;
}
}
}
return intValue;
}
public static boolean castBoolean(Object obj) {
return CastUtil.castBoolean(obj, false);
}
public static boolean castBoolean(Object obj, boolean defaultValue) {
boolean booleanValue = defaultValue;
if (obj != null) {
booleanValue = Boolean.parseBoolean(castString(obj));
}
return booleanValue;
}
}
castUtil類中用到了StringUtil類，它提供一些字元串操作，代碼如下：
public final class StringUtil {
public static boolean isEmpty(String str) {
if (str != null) {
str = str.trim();
}
return StringUtils.isEmpty(str);
}
public static boolean isNotEmpty(String str) {
return !isEmpty(str);
}
}
這樣就可以直接運用這個工具類操作Properties配置檔案了。
操作示例(擷取一個int屬性的值，并給一個預設值1)：Properties conf = PropsUtil.loadProps("config.properties");
int value = PropsUtil.getInt(conf,"key",1);
這樣操作就友善多了。