首先，设置mysql的环境变量（在path中添加%MYSQL_HOME%\bin），重启电脑。
完整代码：

public static void main(String[] args) {

backup();
load();
}

public static void backup() {
try {
Runtime rt = Runtime.getRuntime();

// 调用 mysql 的 cmd:
Process child = rt
.exec("mysqldump -u root --set-charset=utf8 bjse act_obj");// 设置导出编码为utf8。这里必须是utf8

// 把进程执行中的控制台输出信息写入.sql文件，即生成了备份文件。注：如果不对控制台信息进行读出，则会导致进程堵塞无法运行
InputStream in = child.getInputStream();// 控制台的输出信息作为输入流

InputStreamReader xx = new InputStreamReader(in, "utf8");// 设置输出流编码为utf8。这里必须是utf8，否则从流中读入的是乱码

String inStr;
StringBuffer sb = new StringBuffer("");
String outStr;
// 组合控制台输出信息字符串
BufferedReader br = new BufferedReader(xx);
while ((inStr = br.readLine()) != null) {
sb.append(inStr + "\r\n");
}
outStr = sb.toString();

// 要用来做导入用的sql目标文件：
FileOutputStream fout = new FileOutputStream(
"e:/mysql-5.0.27-win32/bin/bjse22.sql");
OutputStreamWriter writer = new OutputStreamWriter(fout, "utf8");
writer.write(outStr);
// 注：这里如果用缓冲方式写入文件的话，会导致中文乱码，用flush()方法则可以避免
writer.flush();

// 别忘记关闭输入输出流
in.close();
xx.close();
br.close();
writer.close();
fout.close();

System.out.println("");

} catch (Exception e) {
e.printStackTrace();
}

}

public static void load() {
try {
String fPath = "e:/mysql-5.0.27-win32/bin/bjse22.sql";
Runtime rt = Runtime.getRuntime();

// 调用 mysql 的 cmd:
Process child = rt.exec("mysql -u root bjse ");
OutputStream out = child.getOutputStream();//控制台的输入信息作为输出流
String inStr;
StringBuffer sb = new StringBuffer("");
String outStr;
BufferedReader br = new BufferedReader(new InputStreamReader(
new FileInputStream(fPath), "utf8"));
while ((inStr = br.readLine()) != null) {
sb.append(inStr + "\r\n");
}
outStr = sb.toString();

OutputStreamWriter writer = new OutputStreamWriter(out, "utf8");
writer.write(outStr);
// 注：这里如果用缓冲方式写入文件的话，会导致中文乱码，用flush()方法则可以避免
writer.flush();
// 别忘记关闭输入输出流
out.close();
br.close();
writer.close();

System.out.println("");

} catch (Exception e) {
e.printStackTrace();
}

}