異常的分類

異常的處理

為什麼使用自定義型別的異常

其實這是問題處理的模式/方式之一；

其它的是什麼？例如WindowsAPI的GetLastError，swift、Go的多返回值 ，返回一個實體類包含所有需要的資訊；

而這個方法同樣也有多種應用。

應用一：你的一個方法中把一些必須滿足的條件作為異常來處理；

應用二：你的一個方法中把所有可能遇到的異常都捕獲了，附加上其它資訊丟擲新的異常；

應用三：以上兩種混合應用；

應用例項

自定義異常類：CustomException.java

package wasdev.sample.servlet;

/**
 * 自定義異常
 * @author testcs_dn
 * 
 */
public class CustomException extends Exception {

	private static final long serialVersionUID = -3260180827302646043L;
	/**
	 * 擴充套件資訊
	 */
	private String exMsg;
	public String getExMsg() {
		return exMsg;
	}

	public void setExMsg(String exMsg) {
		this.exMsg = exMsg;
	}

	/**
	 * 
	 */
	public CustomException() {
		super();
	}

	public CustomException(String msg) {
		super(msg);
	}

	/**
	 * 
	 * @param msg 異常資訊
	 * @param exMsg 擴充套件資訊
	 */
	public CustomException(String msg, String exMsg) {
		super(msg);
		this.setExMsg(exMsg);
	}
}
 

package wasdev.sample.servlet;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class SimpleServlet
 */
@WebServlet("/SimpleServlet")
public class SimpleServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");
        response.getWriter().print("Hello World!");
        
        try {
			doSomething();
		} catch (CustomException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
        
        try {
			doSomething("user", "pwd");
		} catch (CustomException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
    }
    
    protected void doSomething() throws CustomException{
    	throw new CustomException("abcd");
    	
    }
    
    protected void doSomething(String userName, String password) throws CustomException{
    	if (userName == null || userName.length() == 0){
    		throw new CustomException("abcd", "userName");
    	}
    	
    	if (password == null || password.length() == 0){
    		throw new CustomException("abcd", "password");
    	}
    	
    	File f = new File("test.txt");
    	if (f.exists()){
    		try {
				FileOutputStream fos = new FileOutputStream(f);
				try {
					fos.close();
				} catch (IOException e) {
					throw new CustomException("abcd", "IOException");
				}
			} catch (FileNotFoundException e) {
				throw new CustomException("abcd", "FileNotFoundException");
			}
    		
    	}
    }

    protected void doSomething2(){
    	try {
    		throw new CustomException("abcd", "擴充套件資訊");
		} catch (CustomException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
    }
}
 

結束語

如果你有更好的應用場景歡迎分享！

我這裡只定義了一個異常類：CustomException，你也可以做如下定義，只要你喜歡：

UserNameException，PasswordException，FileWriteException……等等。

===========文件資訊============ 

署名(BY) ：testcs_dn(微wx笑) 
文章出處：[無知人生，記錄點滴](http://blog.csdn.net/testcs_dn)