Prepare Initial Program Structure准备初始程序结构

Here's the basic structure of the VerSig program created in the following parts of this lesson. Place this program structure in a file called VerSig.java.以下是本课以下部分创建的VerSig程序的基本结构。将此程序结构放入名为VerSig.java的文件中。

import java.io.*;
import java.security.*;
import java.security.spec.*;

class VerSig {

    public static void main(String[] args) {

        /* Verify a DSA signature */

        if (args.length != 3) {
            System.out.println("Usage: VerSig " +
                "publickeyfile signaturefile " + "datafile");
        }
        else try {

        // the rest of the code goes here

        } catch (Exception e) {
            System.err.println("Caught exception " + e.toString());
        }
    }

}

Notes:笔记：

• The methods for verifying data are in the java.security package, so the program imports everything from that package. 验证数据的方法在java.security包中，因此程序从该包导入所有内容。The program also imports the java.io package for methods needed to input the file data to be signed, as well as the java.security.spec package, which contains the X509EncodedKeySpec class.该程序还导入了java.io包，用于输入要签名的文件数据所需的方法，以及java.security.spec包，其中包含X509EncodedKeySpec类。

• Three arguments are expected, specifying the public key, the signature, and the data files.需要三个参数，指定公钥、签名和数据文件。

• The code written in subsequent steps of this lesson will go between the try and the catch blocks.本课后续步骤中编写的代码将位于try和catch块之间。