有時候我們希望處理properties檔案，properties檔案是鍵值對的檔案形式，我們可以藉助Properties類操作。

 工具類如下:(程式碼中日誌採用了slf4j日誌)

package cn.xm.exam.utils;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
 
import java.io.OutputStream;
import java.util.Map.Entry;
import java.util.Properties;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * 操作properties檔案的工具類(此工具類的file都是src目錄下的properties檔案，編譯之後在build目錄下)
 * 
 * @author QiaoLiQiang
 * @time 2018年11月3日下午12:05:32
 */
public class PropertiesFileUtils {
    
 
private static final Logger log = LoggerFactory.getLogger(PropertiesFileUtils.class);

    /**
     * 建構函式私有化
     */
    private PropertiesFileUtils() {

    }

    /**
     * 儲存或更新properties檔案中的key
     * 
     * @param fileName
     * @param key
     * @param value
     */
    public static
 
 void saveOrUpdateProperty(String fileName, String key, String value) {
        Properties properties = new Properties();
        InputStream inputStream;
        OutputStream outputStream;
        try {
            String path = ResourcesUtil.class.getClassLoader().getResource(fileName).getPath();
            log.debug("path -> {}", path);
            inputStream = new FileInputStream(new File(path));
            properties.load(inputStream);
            properties.setProperty(key, value);

            // 儲存到檔案中(如果有的話會自動更新，沒有會建立)
            outputStream = new FileOutputStream(new File(path));
            properties.store(outputStream, "");

            outputStream.close();
            inputStream.close();
        } catch (FileNotFoundException e) {
            log.error("saveOrUpdateProperty error", e);
        } catch (IOException e) {
            log.error("saveOrUpdateProperty error", e);
        }
    }

    /**
     * 獲取Properties
     * 
     * @param fileName
     * @param key
     * @return
     */
    public static String getPropertyValue(String fileName, String key) {
        Properties properties = new Properties();
        InputStream inputStream;
        try {
            String path = PropertiesFileUtils.class.getClassLoader().getResource(fileName).getPath();
            log.info("path -> {}", path);
            inputStream = new FileInputStream(new File(path));
            properties.load(inputStream);

            for (Entry<Object, Object> entry : properties.entrySet()) {
                log.info("key -> {}， value -> {}", entry.getKey(), entry.getValue());
            }

            // 儲存到檔案中(如果有的話會自動更新，沒有會建立)
            inputStream.close();
        } catch (FileNotFoundException e) {
            log.error("saveOrUpdateProperty error", e);
        } catch (IOException e) {
            log.error("saveOrUpdateProperty error", e);
        }
        return "";
    }

    /**
     * 獲取Properties
     * 
     * @param fileName
     * @return
     */
    public static Properties getProperties(String fileName) {
        Properties properties = new Properties();
        InputStream inputStream;
        try {
            String path = PropertiesFileUtils.class.getClassLoader().getResource(fileName).getPath();
            log.info("path -> {}", path);
            inputStream = new FileInputStream(new File(path));
            properties.load(inputStream);

            inputStream.close();
        } catch (FileNotFoundException e) {
            log.error("saveOrUpdateProperty error", e);
        } catch (IOException e) {
            log.error("saveOrUpdateProperty error", e);
        }
        return properties;
    }

    /**
     * 獲取Properties
     * 
     * @param fileName
     * @return
     */
    public static Properties removeProperty(String fileName, String key) {
        Properties properties = new Properties();
        InputStream inputStream;
        OutputStream outputStream;
        try {
            String path = PropertiesFileUtils.class.getClassLoader().getResource(fileName).getPath();
            log.info("path -> {}", path);
            inputStream = new FileInputStream(new File(path));
            properties.load(inputStream);
            log.info("properties -> {}", properties);
            if (properties != null && properties.containsKey(key)) {
                log.info("remove key:{}", key);
                properties.remove(key);
            }

            // 儲存到檔案中(將properties儲存到檔案)
            outputStream = new FileOutputStream(new File(path));
            properties.store(outputStream, "");

            outputStream.close();
            inputStream.close();
        } catch (FileNotFoundException e) {
            log.error("saveOrUpdateProperty error", e);
        } catch (IOException e) {
            log.error("saveOrUpdateProperty error", e);
        }
        return properties;
    }

    public static void main(String[] args) {
        // 儲存三個 最後一個相當於更新
        PropertiesFileUtils.saveOrUpdateProperty("settings.properties", "a", "aaa");
        PropertiesFileUtils.saveOrUpdateProperty("settings.properties", "b", "bbb");
        PropertiesFileUtils.saveOrUpdateProperty("settings.properties", "c", "ccc");
        PropertiesFileUtils.saveOrUpdateProperty("settings.properties", "a", "AAA");

        // 獲取所有的properties
        Properties properties = PropertiesFileUtils.getProperties("settings.properties");
        System.out.println(properties);

        // 刪除a
        PropertiesFileUtils.removeProperty("settings.properties", "a");
        
        // 獲取所有的properties
        Properties properties1 = PropertiesFileUtils.getProperties("settings.properties");
        System.out.println(properties1);
    }

}

結果:

{b=bbb, a=AAA, c=ccc}
{b=bbb, c=ccc}

解釋:

Properties是繼承了HashTable的一個普通類，所以我們可以簡單的認為操作Properties就是在操作HashTable。

public
class Properties extends Hashtable<Object,Object> {

     private static final long serialVersionUID = 4112578634029874840L;

    protected Properties defaults;
。。。
}

 由於HasTable鍵不可以重複，所以我們在saveOrUpdateProperty中直接setProperty的時候如果沒有key會建立key，如果key存在會覆蓋原來的值。

　　properties.load(inputStream);是將properties檔案中的key=value的資料載入到properties中;

　　properties.store(outputStream, "");是將properties儲存到一個檔案中。