String a= String.valueOf(2);
int i = Integer.parseInt(a);

2. 向文件末尾添加内容

BufferedWriter out=null;
try {
    out=new BufferedWriter(new FileWriter("filename",true));
    out.write("i am stringbuffer!");
} catch (IOException e) {
    e.printStackTrace();
}

3. 得到当前方法的名字

String methodName = Thread.currentThread().getStackTrace()[1].getMethodName();

4. 转字符串到日期与日期到字符串

//日期到字符串
SimpleDateFormat sdf = new SimpleDateFormat( "yyyy年MM月dd日 ");
String str = sdf.format(new Date());
System.out.println(str);
//字符串到日期
Date date = sdf.parse(str);
System.out.println(date);

5. 使用JDBC链接Oracle

public class OracleJdbcTest {
    String driverClass = "oracle.jdbc.driver.OracleDriver"; 
    Connection con; 
    public void init(FileInputStream fs)
            throws ClassNotFoundException, SQLException, FileNotFoundException, IOException { 
        Properties props = new Properties(); 
        props.load(fs); 
        String url = props.getProperty("db.url"); 
        String userName = props.getProperty("db.user"); 
        String password = props.getProperty("db.password"); 
        Class.forName(driverClass); 
        con=DriverManager.getConnection(url, userName, password); 
    } 
   
    public void fetch() throws SQLException, IOException{ 
        PreparedStatement ps = con.prepareStatement("select SYSDATE from dual"); 
        ResultSet rs = ps.executeQuery(); 
   
        while (rs.next()){ 
            // do the thing you do 
        } 
        rs.close(); 
        ps.close(); 
    } 
   
    public static void main(String[] args){ 
        OracleJdbcTest test = new OracleJdbcTest(); 
        test.init(); 
        test.fetch(); 
    }
}

6. 把 Java util.Date 转成 sql.Date

java.util.Date utilDate = new java.util.Date(); 
java.sql.Date sqlDate = new java.sql.Date(utilDate.getTime());

7. 使用NIO进行快速的文件拷贝

public static void fileCopy( File in, File out ) 
        throws IOException  { 
    FileChannel inChannel = new FileInputStream( in ).getChannel(); 
    FileChannel outChannel = new FileOutputStream( out ).getChannel(); 
    try{ 
        // inChannel.transferTo(0, inChannel.size(), outChannel); 
        // original -- apparently has trouble copying large files on Windows 
        // magic number for Windows, 64Mb - 32Kb) 
        int maxCount = (64 * 1024 * 1024) - (32 * 1024); 
        long size = inChannel.size(); 
        long position = 0; 
        while ( position < size ){ 
           position += inChannel.transferTo(position, maxCount, outChannel ); 
        } 
    }finally{ 
        if (inChannel != null){ 
           inChannel.close(); 
        } 
        if (outChannel != null){ 
            outChannel.close(); 
        } 
    } 
}

8. 发送代数据的HTTP 请求

try { 
    URL my_url = new URL("链接地址"); 
    BufferedReader br = new BufferedReader(new InputStreamReader(my_url.openStream())); 
    String strTemp = ""; 
    while(null != (strTemp = br.readLine())){ 
    System.out.println(strTemp); 
} 
} catch (Exception ex) { 
    ex.printStackTrace(); 
}