java - Servlet 中的意外异常行为

Question

我有下面的类，它从属性文件加载数据库详细信息。当文件“dao.properties”丢失时，类应该抛出 DAOConfigurationException 但我得到了

    javax.servlet.ServletException: Servlet execution threw an exception
root cause

java.lang.ExceptionInInitializerError
    com.clone.dao.DAOFactory.getInstance(DAOFactory.java:19)
    com.clone.controller.register.doPost(register.java:35)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
root cause

com.clone.dao.DAOConfigurationException: Properties file dao.properties not found in classpath.
    com.clone.dao.DAOProperties.<clinit>(DAOProperties.java:15)
    com.clone.dao.DAOFactory.getInstance(DAOFactory.java:19)
    com.clone.controller.register.doPost(register.java:35)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

在后续请求中我收到此异常

javax.servlet.ServletException: Servlet execution threw an exception
root cause

java.lang.NoClassDefFoundError: Could not initialize class com.clone.dao.DAOProperties
    com.clone.dao.DAOFactory.getInstance(DAOFactory.java:19)
    com.clone.controller.register.doPost(register.java:35)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

这是我的代码

package com.clone.dao;

import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

public class DAOProperties {
    private static final String PROPERTIES_FILE = "dao.properties";
    private static final Properties PROPERTIES = new Properties();
<b> static{
        ClassLoader classloader = Thread.currentThread().getContextClassLoader();
        InputStream propertiesFile = classloader.getResourceAsStream(PROPERTIES_FILE);

        if(propertiesFile==null){
            throw new DAOConfigurationException("Properties file "+PROPERTIES_FILE+" not found in classpath.");
        } 
        try {
            PROPERTIES.load(propertiesFile);
        } catch (IOException e) {
            throw new DAOConfigurationException("Cannot load properties file '"+PROPERTIES_FILE+"'.", e);
        }
    }
</b>
private String specificKey;


    public DAOProperties(String specificKey)
    {
        this.specificKey=specificKey;
    }

    public String getProperty(String key) throws DAOConfigurationException {
        String fullKey = specificKey+"."+key;
        String property = PROPERTIES.getProperty(fullKey);
        if(property==null||property.trim().length()==0){
            throw new DAOConfigurationException("Property '"+fullKey+"' is missing in properties file '"+
                                                        PROPERTIES_FILE+"'.");
        }
        return property;
    }

}

伙计们，请解释一下发生了什么，这很令人困惑

Answer 1

它正在抛出DAOConfigurationException:

com.clone.dao.DAOConfigurationException: Properties file dao.properties
     not found in classpath.

但是，它被包含在 java.lang.ExceptionInInitializerError 中，因为您的 DAOFactory 正在尝试使用 DAOProperties。由于静态初始化器失败，DAOProperties 类无法正确初始化，而 ExceptionInInitializerError 正是静态初始化器失败时抛出的异常。

也许您不应该在静态初始化程序中执行此操作？