Java Can';无法从数据存储中读取
创建实体并设置属性Java Can';无法从数据存储中读取,java,google-app-engine,google-cloud-datastore,Java,Google App Engine,Google Cloud Datastore,创建实体并设置属性 package pack.exp; import java.io.IOException; import javax.servlet.http.*; import com.google.appengine.api.datastore.DatastoreService; import com.google.appengine.api.datastore.DatastoreServiceFactory; import com.google.appengine.api.datas
package pack.exp;
import java.io.IOException;
import javax.servlet.http.*;
import com.google.appengine.api.datastore.DatastoreService;
import com.google.appengine.api.datastore.DatastoreServiceFactory;
import com.google.appengine.api.datastore.Entity;
import com.google.appengine.api.datastore.Key;
import com.google.appengine.api.datastore.KeyFactory;
@SuppressWarnings("serial")
public class IkaiLanServlet extends HttpServlet
{
public void doGet(HttpServletRequest req, HttpServletResponse resp) throws...
{
Entity alice = new Entity("Person", "Alice");
alice.setProperty("gender", "female");
alice.setProperty("age", 20);
Key bobKey = KeyFactory.createKey("Person", "Bob");
Entity bob = new Entity(bobKey);
bob.setProperty("gender", "male");
bob.setProperty("age", "23");
DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
datastore.put(alice);
datastore.put(bob);
resp.setContentType("text/plain");
resp.getWriter().println("Bye Bye");
}
}
在同一个包中创建另一个servlet
package pack.exp;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.*;
import com.google.appengine.api.datastore.DatastoreService;
import com.google.appengine.api.datastore.DatastoreServiceFactory;
import com.google.appengine.api.datastore.Entity;
import com.google.appengine.api.datastore.EntityNotFoundException;
import com.google.appengine.api.datastore.Key;
import com.google.appengine.api.datastore.KeyFactory;
public class Read extends HttpServlet
{
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws...
{
// TODO Auto-generated method stub
super.doGet(req, resp);
Key bobKey = KeyFactory.createKey("Person", "Bob");
Key aliceKey = KeyFactory.createKey("Person", "Alice");
DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
Entity alice, bob;
try {
alice = datastore.get(aliceKey);
bob = datastore.get(bobKey);
Long aliceAge = (Long) alice.getProperty("age");
Long bobAge = (Long) bob.getProperty("age");
System.out.println("Alice’s age: " + aliceAge);
System.out.println("Bob’s age: " + bobAge);
}
catch (EntityNotFoundException e)
{
// Alice or Bob doesn't exist!
}
}
}
当我部署应用程序时,输出为“再见”。为什么它不读取实体。
请帮助我,我是google app engine数据存储的新手。当您转到映射到
IkaiLanServlet
的任何URL时,它将以“再见”回应,因为您调用了resp.getWriter().println(“再见”)
。要读取实体,请更改
System.out.println("Alice’s age: " + aliceAge);
System.out.println("Bob’s age: " + bobAge);
到
根据文件():
servlet写入标准输出流(System.out)和标准错误流(System.err)的所有内容都由应用程序引擎捕获并记录在应用程序日志中。写入标准输出流的行以“信息”级别记录,写入标准错误流的行以“警告”级别记录
要在浏览器中查看输出,必须使用resp
另外,请确保您访问
IkaiLanServlet
的URL,然后按顺序读取以确保实体位于数据存储中。Remco您能帮我吗。
resp.setContentType("text/plain");
resp.getWriter().println("Alice’s age: " + aliceAge);
resp.getWriter().println("Bob’s age: " + bobAge);