有时候我们希望处理properties文件，properties文件是键值对的文件形式，我们可以借助Properties类操作。

 工具类如下:(代码中日志采用了slf4j日志)

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文件的工具类(此工具类的file都是src目录下的properties文件，编译之后在build目录下) *  * @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);    /**     * 构造函数私有化     */    private PropertiesFileUtils() {    }    /**     * 保存或更新properties文件中的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);            // 保存到文件中(如果有的话会自动更新，没有会创建)            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);        }    }    /**     * 获取Properties     *      * @param fileName     * @param key     * @return     */    public static String getPropertyValue(String fileName, String key) {        Properties properties = new Properties();        InputStream inputStream;        String value = "";        try {            String path = PropertiesFileUtils.class.getClassLoader().getResource(fileName).getPath();            log.info("path -> {}", path);            inputStream = new FileInputStream(new File(path));            properties.load(inputStream);            value = properties.getProperty(key);            // 保存到文件中(如果有的话会自动更新，没有会创建)            inputStream.close();        } catch (FileNotFoundException e) {            log.error("saveOrUpdateProperty error", e);        } catch (IOException e) {            log.error("saveOrUpdateProperty error", e);        }        return value;    }    /**     * 获取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;    }    /**     * 获取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);            }            // 保存到文件中(将properties保存到文件)            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) {        // 保存三个 最后一个相当于更新        PropertiesFileUtils.saveOrUpdateProperty("settings.properties", "a", "aaa");        PropertiesFileUtils.saveOrUpdateProperty("settings.properties", "b", "bbb");        PropertiesFileUtils.saveOrUpdateProperty("settings.properties", "c", "ccc");        PropertiesFileUtils.saveOrUpdateProperty("settings.properties", "a", "AAA");        // 获取所有的properties        Properties properties = PropertiesFileUtils.getProperties("settings.properties");        System.out.println(properties);        // 删除a        PropertiesFileUtils.removeProperty("settings.properties", "a");        // 获取所有的properties        Properties properties1 = PropertiesFileUtils.getProperties("settings.properties");        System.out.println(properties1);    }}

 

 

 

结果:

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

{b=bbb, c=ccc}

 

解释:

Properties是继承了HashTable的一个普通类，所以我们可以简单的认为操作Properties就是在操作HashTable。

publicclass Properties extends Hashtable
     
       {     private static final long serialVersionUID = 4112578634029874840L;    protected Properties defaults;。。。}
     

 

 

 由于HasTable键不可以重复，所以我们在saveOrUpdateProperty中直接setProperty的时候如果没有key会创建key，如果key存在会覆盖原来的值。

　　properties.load(inputStream);是将properties文件中的key=value的数据加载到properties中;

　　properties.store(outputStream, "");是将properties保存到一个文件中。

 

补充:上面代码还可以进一步将properties文件的位置封装全路径:

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.Properties;import org.slf4j.Logger;import org.slf4j.LoggerFactory;/** *  * @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);    /**     * 构造函数私有化     */    private PropertiesFileUtils() {    }    /**     * 保存或更新properties文件中的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);            // 保存到文件中(如果有的话会自动更新，没有会创建)            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);        }    }    /**     * 获取Properties     *      * @param fileName     * @param key     * @return     */    public static String getPropertyValue(String fileName, String key) {        Properties properties = new Properties();        InputStream inputStream;        String value = "";        try {            String path = PropertiesFileUtils.class.getClassLoader().getResource(fileName).getPath();            log.info("path -> {}", path);            inputStream = new FileInputStream(new File(path));            properties.load(inputStream);            value = properties.getProperty(key);            // 保存到文件中(如果有的话会自动更新，没有会创建)            inputStream.close();        } catch (FileNotFoundException e) {            log.error("saveOrUpdateProperty error", e);        } catch (IOException e) {            log.error("saveOrUpdateProperty error", e);        }        return value;    }    /**     * 获取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;    }    /**     * 获取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);            }            // 保存到文件中(将properties保存到文件)            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;    }    /**     * 保存或更新properties文件中的key     *      * @param path     *            文件全路径     * @param key     * @param value     */    public static void saveOrUpdatePropertyByFilePath(String path, String key, String value) {        Properties properties = new Properties();        InputStream inputStream;        OutputStream outputStream;        try {            log.debug("path -> {}", path);            inputStream = new FileInputStream(new File(path));            properties.load(inputStream);            properties.setProperty(key, value);            // 保存到文件中(如果有的话会自动更新，没有会创建)            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);        }    }    /**     * 获取Properties     *      * @param path     *            文件全路径     * @param key     * @return     */    public static String getPropertyValueByFilePath(String path, String key) {        Properties properties = new Properties();        InputStream inputStream;        String value = "";        try {            log.info("path -> {}", path);            inputStream = new FileInputStream(new File(path));            properties.load(inputStream);            value = properties.getProperty(key);            // 保存到文件中(如果有的话会自动更新，没有会创建)            inputStream.close();        } catch (FileNotFoundException e) {            log.error("saveOrUpdateProperty error", e);        } catch (IOException e) {            log.error("saveOrUpdateProperty error", e);        }        return value;    }    /**     * 获取Properties     *      * @param path     *            文件全路径     * @return     */    public static Properties getPropertiesByFilePath(String path) {        Properties properties = new Properties();        InputStream inputStream;        try {            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;    }    /**     * 获取Properties     *      * @param path     *            文件全路径     * @param key     *            key值     * @return     */    public static Properties removePropertyByFilePath(String path, String key) {        Properties properties = new Properties();        InputStream inputStream;        OutputStream outputStream;        try {            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);            }            // 保存到文件中(将properties保存到文件)            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;    }}