从服务端加载图片(Volley框架+Gson框架)
服务端代码--web.xml配置文件省略了(这些不是重点)
ShopInfo.java（为了节俭空间get、set、toString、构造器省略了）
private String name;
private String img;ShopListServlet.java
package com.atguigu.dianpin_server.servlet;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.google.gson.Gson;
/**
* 获取分页ShopList的json字符串
*/
public class ShopListServlet extends HttpServlet {
// 定义ShopInfo的集合
private List infos;
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
init();
// count的请求参数
int count = Integer.parseInt(request.getParameter("count"));
// 从集合中取当前请求页的数据集合
List data = new ArrayList();
for (int i = 0; i < count; i++) {
data.add(infos.get(i));
}
// 转换为json字符串
String json = new Gson().toJson(data);
// 写到客户端
response.setContentType("text/json;charset=utf-8");
response.getWriter().write(json);
// 格式：[{"name":"商铺名称1",
// "img":"f1.jpg"},{"name":"商铺名称2","img":"f12.jpg"}]
}
public void init() {
if (infos == null) {
// 创建ShopInfo的集合
infos = new ArrayList();
// 得到/image的真实路径
String imagesPath = getServletContext().getRealPath("/image");
// 创建指向图片的对象
File dirFile = new File(imagesPath);
// 得到file对象的数组
File[] files = dirFile.listFiles();
// 遍历
for (int i = 0; i < files.length; i++) {
// 将图片信息封装为一个shopinfo对象, 并保存到集合中
String imageName = files[i].getName();
String name = "商铺名称 " + (i + 1);
infos.add(new ShopInfo(name, imageName));
}
}
}
}
首先贴出布局文件
activity_main.xml
list_item.xml
接下来看android代码
ShopInfo.java
(为了节俭空间get、set、toString、构造器android代码也省略了)
本类是将从服务端得到的json数组中的每个元素json对象封装为ShopInfo对象
private String name;
private String img;VolleyTool.java
package com.atguigu.day03_test;
import android.content.Context;
import android.graphics.Bitmap;
import android.support.v4.util.LruCache;
import com.android.volley.RequestQueue;
import com.android.volley.toolbox.ImageLoader;
import com.android.volley.toolbox.ImageLoader.ImageCache;
import com.android.volley.toolbox.Volley;
public class VolleyTool {
//初始化请求队列、图片加载器
private RequestQueue queue;
private ImageLoader imageLoader;
//私有静态实例
private static VolleyTool instance;
//私有构造方法
private VolleyTool(Context context) {
//创建请求队列
queue = Volley.newRequestQueue(context);
//创建图片加载器
imageLoader = new ImageLoader(queue, new LruImageCache());
}
//公共、静态的方法
public static VolleyTool getInstance(Context context) {
if (instance == null) {
instance = new VolleyTool(context);
}
return instance;
}
//得到请求队列
public RequestQueue getQueue() {
return queue;
}
//得到图片加载器
public ImageLoader getImageLoader() {
return imageLoader;
}
/**
* 使用LRU回收算法的缓存类
*/
class LruImageCache implements ImageCache {
// 缓存容器
private LruCache cache;
public LruImageCache() {
// 计算缓存的最值
int maxSize = (int) (Runtime.getRuntime().maxMemory() / 8);
//创建缓存对象实例
cache = new LruCache(maxSize) {
@Override
protected int sizeOf(String key, Bitmap value) {
// 返回bitmap占用的内存大小
return value.getRowBytes() * value.getHeight();
}
};
}
// 从缓存中取图片对象
@Override
public Bitmap getBitmap(String url) {
return cache.get(url);
}
// 将图片对象保存到缓存容器中
@Override
public void putBitmap(String url, Bitmap bitmap) {
cache.put(url, bitmap);
}
}
}
MainActivity.java
package com.atguigu.day03_test;
import java.util.ArrayList;
import java.util.List;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ListView;
import android.widget.ProgressBar;
import android.widget.TextView;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.Response.Listener;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonArrayRequest;
import com.android.volley.toolbox.NetworkImageView;
import com.android.volley.toolbox.StringRequest;
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
public class MainActivity extends Activity {
private ListView lv_main;
private ProgressBar pb_main;
//请求队列
RequestQueue requestQueue;
//存放数据对象的集合
private List data = new ArrayList();
//适配器
private MainAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//找到对应的视图资源文件
lv_main = (ListView) findViewById(R.id.lv_main);
pb_main = (ProgressBar) findViewById(R.id.pb_main);
//获取请求队列
requestQueue = VolleyTool.getInstance(getApplicationContext()).getQueue();
//为适配器准备加载服务端的数据
loadData();
}
private void loadData() {
String url = "http://192.168.30.41:8090/dianpin_03/ShopListServlet?count=30";
/*注释部分是原始的解析方法
* new JsonArrayRequest(url, new Response.Listener() {
@Override
public void onResponse(JSONArray response) {
for (int i = 0; i < response.length(); i++) {
try {
JSONObject jsonObject = response.getJSONObject(i);
String name = jsonObject.getString("name");
String img = jsonObject.getString("img");
data.add(new ShopInfo(name, img));
} catch (JSONException e) {
e.printStackTrace();
}
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
}
});*/
//创建一个请求
Request request = new StringRequest(url, new Listener() {
@Override
public void onResponse(String response) {
//将服务器端的json数组解析为ShopInfo对象集合
data = new Gson().fromJson(response, new TypeToken>(){}.getType());
adapter = new MainAdapter();
//设置适配器
lv_main.setAdapter(adapter);
pb_main.setVisibility(View.GONE);
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
}
});
//将请求添加到队列中, 自动处理
requestQueue.add(request);
}
class MainAdapter extends BaseAdapter {
@Override
public int getCount() {
return data.size();
}
@Override
public Object getItem(int position) {
return data.get(position);
}
@Override
public long getItemId(int position) {
return 0;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder holder = null;
if (convertView == null) {
holder = new ViewHolder();
convertView = View.inflate(getApplicationContext(),
R.layout.list_item, null);
holder.imageView = (NetworkImageView) convertView
.findViewById(R.id.iv_img);
holder.textView = (TextView) convertView
.findViewById(R.id.tv_name);
convertView.setTag(holder);
} else {
holder = (ViewHolder) convertView.getTag();
}
ShopInfo shopInfo = data.get(position);
holder.textView.setText(shopInfo.getName());
//设置未加载默认图片
holder.imageView.setDefaultImageResId(R.drawable.default_icon);
//设置加载异常的图片
holder.imageView.setErrorImageResId(R.drawable.error);
String url = "http://192.168.30.41:8090/dianpin_03/image/"+shopInfo.getImg();
holder.imageView.setImageUrl(url, VolleyTool.getInstance(getApplicationContext()).getImageLoader());
return convertView;
}
class ViewHolder {
NetworkImageView imageView;
TextView textView;
}
}
}