Question

我正面临这个错误：

`Unable to load properties file for MultiWordNet
Exception in thread "main" java.lang.NumberFormatException: null
at java.lang.Integer.parseInt(Integer.java:417)
at java.lang.Integer.<init>(Integer.java:660)
at org.itc.mwn.MysqlDictionary.<init>(MysqlDictionary.java:85)`

这是MysqlDictionary.java尝试阅读的属性文件：

#------------------------------------------------------------
#Properties file properties MultiWordNet API

#Hostname of the MySQL server
MWN_HOSTNAME=localhost

#User
MWN_USER=root

#Password
MWN_PASSWD=

#Database name
MWN_DB=wordnet

#Cache of entity 
CACHE_CAPACITY=1000

最后，这是代码失败的部分：

public MysqlDictionary() {
    try {
        connectionParameters = new Properties();
        connectionParameters.load(new FileInputStream(new File("./conf/multiwordnet.properties")));
    } catch (java.io.IOException ioee) {
        System.err.println("Unable to load properties file for MultiWordNet");
    }

    /// connection drivers instance
    try {
        Class.forName("com.mysql.jdbc.Driver").newInstance();
        //Class.forName("org.gjt.mm.mysql.Driver").newInstance();
    } catch(ClassNotFoundException E){
        System.err.println("Unable to load driver");
    } catch(IllegalAccessException E){
        System.err.println("Unable to load driver");
    } catch(InstantiationException E){
        System.err.println("Unable to load driver");
    }

    // MultiWordnet db connection
    String  host = connectionParameters.getProperty("MWN_HOSTNAME");
    String user = connectionParameters.getProperty("MWN_USER");
    String passwd = connectionParameters.getProperty("MWN_PASSWD");
    String dbname = connectionParameters.getProperty("MWN_DB");
    Integer cache = new Integer(connectionParameters.getProperty("CACHE_CAPACITY"));  
    //here is where the parsing fails, but the file is properly written!
try {
        DEFAULT_CACHE_CAPACITY = cache.intValue();

        String conn = "jdbc:mysql://" + host + "/" + dbname;
        this.db = DriverManager.getConnection(conn,user,passwd);
        this.stmt = db.createStatement();


        System.err.println("Welcome to the MultiWordNet API\nConnection database ...OK\n");
    } catch (SQLException E) {
        System.out.println("Unable to establish multiwordnet Mysql DB connection on " + host + "(" + user + " - " + passwd + ")");
        E.printStackTrace(System.out);
    }

奇怪的是，程序运行正常后突然失败

Answer 1

检查<SHIFT>+<SPACE>或<CTRL>+<SPACE>之间的不规则隐形字符，或CACHE_CAPACITY=1000旁边的字符。

听起来有点亵渎，但我经常偶然发现这些事情。

Answer 2

检查属性文件中的空格或尝试如下

String cacheProp = connectionParameters.getProperty("CACHE_CAPACITY")
//For debug
System.out.println("cacheProp="+cacheProp);
Integer cache = new Integer(cacheProp.trim());

Answer 3

此代码对我来说很好，我将属性文件保存在资源文件夹（src / main / resources）

中

public static void MysqlDictionary() {
            try {
                Properties p = new Properties();
                p.load(MyTest.class.getResourceAsStream("/test.properties"));
                String host = p.getProperty("MWN_HOSTNAME");
                String user = p.getProperty("MWN_USER");
                String passwd = p.getProperty("MWN_PASSWD");
                String dbname = p.getProperty("MWN_DB");
                String cache = p.getProperty("CACHE_CAPACITY");
                int i = Integer.parseInt(cache);
                System.out.println(host+"\t"+user+"\t"+passwd+"\t"+dbname+"\t"+i);
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }

        }

Answer 4

在java中处理File时，不要与相对路径斗争。它们非常不可预测，因为它们依赖于您无法完全控制的当前工作目录。请改用classpath，使用类加载器加载资源：

Properties properties = new Properties();
properties.load(getClass().getResourceAsStream("multiwordnet.properties"));

您的问题是无法解析整数，但无法加载文件。

java.lang.NumberFormatException：null

4 个答案: