Google App Engine使用

下载App Engine SDK

下载App Engine SDK。

然后通过：

javac -version

查看Java JDK安装版本，确定自己安装的是Java 6 JDK。

如果版本较低，那么去官网下一个。

Servlet

Servlet = Server + Applet

即Servlet是：服务器端小程序。

文件结构

项目的文件结构是怎样的呢？

project/
  src/
    ...Java source code...
    META-INF/
      ...other configuration...
  war/
    ...JSPs, images, data files...
    WEB-INF/
      ...app configuration...
      lib/
        ...JARs for libraries...
      classes/
        ...compiled classes...

其中project是项目目录。

使用Apache Ant

• 首先先确认ant的版本，在终端输入：

ant -version

• 打开终端，创建相应的路径：

mkdir project
cd project
mkdir -p src/META-INF
mkdir -p war/WEB-INF/classes
mkdir -p war/WEB-INF/lib

• 然后在项目根目录下创建ant配置文件build.xml：

<project>
  <property name="sdk.dir" location="../appengine-java-sdk" />

  <import file="${sdk.dir}/config/user/ant-macros.xml" />

</project>

sdk.dir指向app engine sdk的路径。

• 定义库路径：

  <path id="project.classpath">
    <pathelement path="war/WEB-INF/classes" />
    <fileset dir="war/WEB-INF/lib">
      <include name="**/*.jar" />
    </fileset>
    <fileset dir="${sdk.dir}/lib">
      <include name="shared/**/*.jar" />
    </fileset>
  </path>

• 复制库规则：

  <target name="copyjars"
      description="Copies the App Engine JARs to the WAR.">
    <copy
        todir="war/WEB-INF/lib"
        flatten="true">
      <fileset dir="${sdk.dir}/lib/user">
        <include name="**/*.jar" />
      </fileset>
    </copy>
  </target>

然后在终端输入：

ant copyjars

则可将库文件复制到war/WEB-INF/lib中。

• 编译源文件规则：

  <target name="compile" depends="copyjars"
      description="Compiles Java source and copies other source files to the WAR.">
    <mkdir dir="war/WEB-INF/classes" />
    <copy todir="war/WEB-INF/classes">
      <fileset dir="src">
        <exclude name="**/*.java" />
      </fileset>
    </copy>
    <javac
        srcdir="src"
        destdir="war/WEB-INF/classes"
        classpathref="project.classpath"
        debug="on" />
  </target>

现在我们可以用：

ant compile

执行编译。

• 运行服务器：

  <target name="runserver" depends="datanucleusenhance"
      description="Starts the development server.">
    <dev_appserver war="war" />
  </target>

则，我们可以用：

ant runserver

运行服务器。

• 上传配置：

  <target name="update" depends="datanucleusenhance"
      description="Uploads the application to App Engine.">
    <appcfg action="update" war="war" />
  </target>

  <target name="update_indexes" depends="datanucleusenhance"
      description="Uploads just the datastore index configuration to App Engine.">
    <appcfg action="update_indexes" war="war" />
  </target>

  <target name="rollback" depends="datanucleusenhance"
      description="Rolls back an interrupted application update.">
    <appcfg action="rollback" war="war" />
  </target>

  <target name="request_logs"
      description="Downloads log data from App Engine for the application.">
    <appcfg action="request_logs" war="war">
      <options>
        <arg value="--num_days=5"/>
      </options>
      <args>
        <arg value="logs.txt"/>
      </args>
    </appcfg>
  </target>

• 完整配置

<project>
  <property name="sdk.dir" location="../appengine-java-sdk" />

  <import file="${sdk.dir}/config/user/ant-macros.xml" />

  <path id="project.classpath">
    <pathelement path="war/WEB-INF/classes" />
    <fileset dir="war/WEB-INF/lib">
      <include name="**/*.jar" />
    </fileset>
    <fileset dir="${sdk.dir}/lib">
      <include name="shared/**/*.jar" />
    </fileset>
  </path>

  <target name="copyjars"
      description="Copies the App Engine JARs to the WAR.">
    <copy
        todir="war/WEB-INF/lib"
        flatten="true">
      <fileset dir="${sdk.dir}/lib/user">
        <include name="**/*.jar" />
      </fileset>
    </copy>
  </target>

  <target name="compile" depends="copyjars"
      description="Compiles Java source and copies other source files to the WAR.">
    <mkdir dir="war/WEB-INF/classes" />
    <copy todir="war/WEB-INF/classes">
      <fileset dir="src">
        <exclude name="**/*.java" />
      </fileset>
    </copy>
    <javac
        srcdir="src"
        destdir="war/WEB-INF/classes"
        classpathref="project.classpath"
        debug="on" />
  </target>

  <target name="datanucleusenhance" depends="compile"
      description="Performs JDO enhancement on compiled data classes.">
    <enhance_war war="war" />
  </target>

  <target name="runserver" depends="datanucleusenhance"
      description="Starts the development server.">
    <dev_appserver war="war" />
  </target>

  <target name="update" depends="datanucleusenhance"
      description="Uploads the application to App Engine.">
    <appcfg action="update" war="war" />
  </target>

  <target name="update_indexes" depends="datanucleusenhance"
      description="Uploads just the datastore index configuration to App Engine.">
    <appcfg action="update_indexes" war="war" />
  </target>

  <target name="rollback" depends="datanucleusenhance"
      description="Rolls back an interrupted application update.">
    <appcfg action="rollback" war="war" />
  </target>

  <target name="request_logs"
      description="Downloads log data from App Engine for the application.">
    <appcfg action="request_logs" war="war">
      <options>
        <arg value="--num_days=5"/>
      </options>
      <args>
        <arg value="logs.txt"/>
      </args>
    </appcfg>
  </target>

</project>

For Example

package example;

import java.io.IOException;
import javax.servlet.http.*;

//写一个Servlet类，继承自javax.servlet.http.HttpServlet
public class myServlet extends HttpServlet{
    //处理HTTP GET请求的方法
    public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
        resp.setContentType("text/html");
        resp.getWriter().println("<p>Hello, world</p>");
    }    
}

我们在src文件夹下，创建一个myServlet.java文件。因为我们把他放在example package中，所以还要放在example目录中。真实的路径是：

project/src/example/myServlet.java

配置部署描述符文件

创建文件war/WEB-INF/web.xml，修改内容如下：

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd">

<web-app xmlns="http://java.sun.com/xml/ns/javaee" version="2.5">
    <servlet>
        <servlet-name>example.</servlet-name>
        <servlet-class>example.myServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>example</servlet-name>
        <url-pattern>/*</url-pattern>
    </servlet-mapping>

</web-app>

配置App Engine配置文件

创建war/WEB-INF/appengine-web.xml，修改内容如下：

<?xml version="1.0" encoding="utf-8"?>
<appengine-web-app xmlns="http://appengine.google.com/ns/1.0">
    <application></application>
    <version>1</version>
</appengine-web-app>

OK，我们可以用：

ant runserver

通过http://localhost:8080打开我们的服务页面了。