Day8.12

DoGet方法

每个Servlet一般都需要重写doGet方法，因为父类的HttpServlet的doGet方法是空的，没有实现任何代码，子类需要重写此方法。doGet方法的定义代码如下：

public void doGet(HttpServletRequest request,HttpServletResponse response )throws

ServletException,IOException{

}

当客户使用GET方式请求Servlet时，Web容器调用doGet方法处理请求。[1]

一般来说我们是用不到doGet方法的，doGet方法提交表单的时候会在url后边显示提交的内容，所以不安全。而且doGet方法只能提交256个字符(1024字节)，而doPost没有限制，因为get方式数据的传输载体是URL（提交方式能form，也能任意的URL链接），而POST是HTTP头键值对（只能以form方式提交）。通常我们使用的都是doPost方法，你只要在servlet中让这两个方法互相调用就行了，例如在doGet方法中这样写：

　　public void doGet(HttpServletRequest request, HttpServletResponse response)

　　throws ServletException, IOException {

　　doPost(request,response);

　　}

　　再把业务逻辑直接写在doPost方法中。servlet碰到doGet方法调用直接就会去调用doPost因为他们的参数都一样。而且doGet方法处理中文问题很困难，要写过滤器之类的。

　　

public void actionPerformed(ActionEvent arg0) {
String urlString="http://localhost:8080/MyTest/MyTestServlet?username=小明&password=123456";//获取url
HttpClientBuilder builder=HttpClientBuilder.create();
builder.setConnectionTimeToLive(3000, TimeUnit.MILLISECONDS);
//生成client的builder
HttpClient client=builder.build(); //生成client
HttpGet get=new HttpGet(urlString);//设置为GET方法
get.setHeader("Content-Type", "application/x-www-form-urlencoded; charset=UTF-8");
try {
HttpResponse response=client.execute(get);//执行get方法得到的服务器返回的所有数据都在response中
StatusLine statusLine=response.getStatusLine();//http访问服务器返回的表头，包含http状态码
int code=statusLine.getStatusCode();
if(code==HttpURLConnection.HTTP_OK){
HttpEntity entity=response.getEntity();//得到数据实体
InputStream is=entity.getContent();
BufferedReader br=new BufferedReader(new InputStreamReader(is));
String line=br.readLine();
if(line!=null){
System.out.println(line);
line=br.readLine();
}

}

DoPOST方法

DoPost是隐式的，相对doget安全且提交内容大小没有限制。

public void actionPerformed(ActionEvent arg0) {
String urlString="http://localhost:8080/MyTest/MyTestServlet";
try {
URL url=new URL(urlString);//获取url
HttpClientBuilder builder=HttpClientBuilder.create();
builder.setConnectionTimeToLive(3000, TimeUnit.MILLISECONDS);
HttpClient client=builder.build();
HttpPost post=new HttpPost(urlString);
NameValuePair pair1=new BasicNameValuePair("username", "小明");
NameValuePair pair2=new BasicNameValuePair("password", "123456");
ArrayList<NameValuePair> params=new ArrayList<>();
params.add(pair1);
params.add(pair2);
post.setEntity(new UrlEncodedFormEntity(params,"UTF-8"));//网络编码形式实体
post.setHeader("Content-Type", "application/x-www-form-urlencoded; charset=UTF-8");
HttpResponse response=client.execute(post);
int code=response.getStatusLine().getStatusCode();
if(code==200){
HttpEntity entity=response.getEntity();
InputStream is=entity.getContent();
BufferedReader br=new BufferedReader(new InputStreamReader(is));
String line=br.readLine();
while(line!=null){
System.out.println(line);
line=br.readLine();
}

}
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ClientProtocolException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}

实现Servlet与数据库的连接

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

public class MySqlMannager {
//单例模式
private static  MySqlMannager mannager;
private Statement statement;
private    Connection connection;
public Connection getConnection() {
return connection;
}

public void setConnection(Connection connection) {
this.connection = connection;
}

public Statement getStatement() {
return statement;
}

public static synchronized MySqlMannager newInstance(){
if(mannager==null){
mannager=new MySqlMannager();
}
return mannager;
}

public void setStatement(Statement statement) {
this.statement = statement;
}
private MySqlMannager(){
String driver="com.mysql.jdbc.Driver";//连接数据库的驱动
String url="jdbc:mysql://localhost:3306/clazz";//URL指向要访问的数据库名
String user="root"; //MYSQL的用户名
String password="111111";//MySQL密码
try {
Class.forName(driver);//加载驱动
connection = DriverManager.getConnection(url, user, password);// 连接数据库
//          statement = connection.createStatement();
//          String create = "CREATE TABLE USER(id int(11) not null PRIMARY KEY auto_increment,user_name varchar(30) not null,password varchar(30) not null)";
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} // 加载驱动
catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}

}