正月初十回校,十一开始实训课程。要求是在两周之后交出一个Android APP。
对于Android,我的印象就是跟java一样,但是没搞过。
第一周,java,从数据类型到讲到servlet,中间讲了集合、线程、IO、单例模式,总之是捞干的来。
第一周结束,也算是收获颇丰,捡起了扔下两年的代码,因为是学习就放弃了使用框架的想法,自己试着用反射机制简单的封装了servlet。长时间不写代码的感受是,对于持有其他对象引用的这个事,经常会忘记初始化就拿来用了,报错基本都是空指针异常。
第二周,Android。
其实怎么看都跟WEB类似,Android的前端跟WEB的前端并没有太多区别。给组件一个id,在相应的activity中获取组件,对组件进行监听,获取内容。其实Android的组件都很成熟了,那些看起来炫酷的东西,Android本身都已经封装好了,拿来用就是了。
Android前端设计的时候跟WEB不同的是,受限于屏幕大小,我们需要把更多的事件放到同一个组件中。比如说一个搜索框,在WEB中我们可以用一个下拉框来控制搜索内容的类别,但在WEB中这并不适用,如果你在应用中见到搜索框加下拉选择类型,这种软件还是放弃吧,辣眼睛。合适的做法是你可以在搜索框下加入几个大方美观的标签,搜索的同时获取标签内容。另一个就是你在响应搜索事件后,搜索多张表,浪费点时间,但却简化了用户的操作。
另一个遇到的问题是Android studio 对于前端页面报错不明显。如果你的布局里有多个组件,而你又不小心忘了写oritentation,很不幸有些东西会显示不出来。这个问题让我误以为我的Intent没有把参数传过来,折腾了好久(哭)。
对于APP的网络连接,我们使的是老控件。
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
/**
* Created by Administrator on 2018/3/9.
*/
public class NetworkUtil {
public static final String BASE_URL = "http://192.168.3.69:8080/networkBack/";
public static final String QUERY_PERSON = BASE_URL + "QueryAllServlet";
public static final String PAGE_PERSON = BASE_URL + "PageQueryServlet";
public static final String INSERT_PERSON = BASE_URL + "InsertPerServlet";
public static JSONObject getJSONByURL(String urlStr) throws IOException, JSONException {
return new JSONObject(getDataByURL(urlStr));
}
public static JSONArray getJSONArrByURL(String urlStr) throws IOException, JSONException {
return new JSONArray(getDataByURL(urlStr));
}
public static String getDataByURL(String urlStr) throws IOException {
//通过地址创建URL对象
URL url = new URL(urlStr);
//建立连接
URLConnection conn = url.openConnection();
//接收返回的数据流
InputStream is = conn.getInputStream();
//读取返回的内容
BufferedReader br = new BufferedReader(new InputStreamReader(is));
StringBuffer buffer = new StringBuffer();
String line = null;
while ((line = br.readLine()) != null) {
buffer.append(line);
}
br.close();
return buffer.toString();
}
public static String postDataByUrl(String urlStr, Map<String, String> map) throws IOException {
HttpClient client = new DefaultHttpClient();
HttpPost post = new HttpPost(urlStr);
List<NameValuePair> list = new ArrayList<>();
Iterator<Map.Entry<String, String>> iter = map.entrySet().iterator();
while(iter.hasNext()) {
Map.Entry<String, String> entry = iter.next();
NameValuePair pair = new BasicNameValuePair(entry.getKey(), entry.getValue());
list.add(pair);
}
post.setEntity(new UrlEncodedFormEntity(list));
HttpResponse response = client.execute(post);
return EntityUtils.toString(response.getEntity());
}
}
这里犯得另一个错误是在后台返回数据时写成out.println();
多了一个换行符,对返回结果进行字符串匹配时,一直不对,我差点就怀疑人生了。
结尾附上另外两个封装代码(数据库和servlet):
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;
public class DBUtil {
private String url = "jdbc:mysql://localhost/xjtuse";
private String user = "root";
private String password = "root";
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
//µ¥ÁÐģʽ
private static final DBUtil dbutil = new DBUtil();
private DBUtil(){
}
public static DBUtil getInstace(){
return dbutil;
}
//»ñÈ¡Êý¾Ý¿âÁ¬½Ó
public Connection getConnection() {
try {
Class.forName("com.mysql.jdbc.Driver");
conn = DriverManager.getConnection(url, user, password);
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return conn;
}
//²éѯ
public ResultSet query(String sql, List<Object> params){
try {
ps = conn.prepareStatement(sql);
if(params != null && params.size() > 0){
for(int i = 0; i < params.size(); i++){
ps.setObject(i + 1, params.get(i));
}
}
rs = ps.executeQuery();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return rs;
}
//Ð޸ĸüÐÂ
public void update(String sql, List<Object> params){
try {
ps = conn.prepareStatement(sql);
if(params != null && params.size() > 0){
for (int i = 0; i < params.size(); i++){
ps.setObject(i + 1, params.get(i));
}
}
ps.executeUpdate();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
//¹Ø±ÕÁ¬½Ó
public void close(){
try {
if(rs != null)
{
rs.close();
}
if(ps != null){
ps.close();
}
if(conn != null){
conn.close();
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class BasicServlet extends HttpServlet{
private static final long serialVersionUID = 1L;
@Override
protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=utf-8");
request.setCharacterEncoding("utf-8");
String methodname = request.getParameter("methodname");
//»ñÈ¡µ±Ç°ÀàµÄÈ«ÀàÃû
Class clazz = this.getClass();
try {
//·´Éä»ñµÃ·½·¨
Method method = clazz.getMethod(methodname, HttpServletRequest.class, HttpServletResponse.class);
//·´Éäµ÷ÓÃ
String path = (String)method.invoke(this, request, response);
if(path != null && !path.equals("")){
request.getRequestDispatcher(path).forward(request, response);
return;
}
} catch (NoSuchMethodException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (SecurityException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalArgumentException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InvocationTargetException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}