<dependencies>
        <dependency>
            <groupId>xml-security</groupId>
            <artifactId>xmlsec</artifactId>
            <version>1.0.5D2</version>
        </dependency>
        <dependency>
            <groupId>dom4j</groupId>
            <artifactId>dom4j</artifactId>
            <version>1.6.1</version>
        </dependency>
  </dependencies>

pom.xml文件中添加依赖

package tt;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStreamReader;

public class Test {

    public static void main(String[] args) {
        File file = new File("D:/a.txt");
        try {
            InputStreamReader inputStreamReader = new InputStreamReader(new FileInputStream(file), "GBK");
            BufferedReader bufferReader = new BufferedReader(inputStreamReader);
            String lineTXT = null;
            String signature = null;
            while ((lineTXT = bufferReader.readLine()) != null) {
                if (lineTXT.trim().startsWith("<signature>")) {
                    signature = lineTXT.trim().substring(11, lineTXT.trim().length() - 12);
                    System.out.println(signature);
                }
            }
            bufferReader.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}