java - android中JSON和SERVLET出错

Question

我有一个 Servlet，它连接到 SQL Server，获取结果集， 并向 Android 客户端发送一个字符串。 直到这里一切都很好。

现在我想将对象发送到客户端，所以我知道我需要使用 JSON。 我将 JSON 的 jar 添加到 servlet 和客户端的构建路径中。 .Eclipse识别了它，我编译成功了。

这是在 servlet 部分:

List<String> myListOfStrings = new ArrayList<String>(); 
myListOfStrings.add("first word");
myListOfStrings.add("second word");
myListOfStrings.add("third word");

JSONArray arrOfJSON=new JSONArray();          
for (String s : myListOfStrings){
   arrOfJSON.put(s);
}
//Here I serialize the stream to a String.
final String output = arrOfJSON.toString();
response.setContentLength(output.length());
//And write the string to output.
response.getOutputStream().write(output.getBytes());
response.getOutputStream().flush();
response.getOutputStream().close();

问题出在运行时:

java.lang.ClassNotFoundException: org.json.JSONArray
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1720)
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1571)
    at Servlet2ForLNM_Pack.Servlet2ForLNM_Class.doPost(Servlet2ForLNM_Class.java:1374)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1074)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)

有人可以帮助我了解我哪里出了问题吗？

Answer 1

1. 检查您的 jar 是否放置在 /WebContent/WEB-INF/lib
2. 告诉 Eclipse 在构建项目时将 jar 包含在 war 文件中 source

我建议您迁移到maven构建系统。 Maven 允许您从单个文件配置整个项目(无需 Eclipse 配置)。

您从项目根目录运行mvn clean install来构建war文件。您的 pom.xml 看起来像这样

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>yourGroupId</groupId>
    <artifactId>yourArtifactId</artifactId>
    <version>1.0.0</version>
    <packaging>war</packaging>
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>
    <dependencies>
        <!-- this is important, other libs can be excluded -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <scope>provided</scope>
            <version>3.0.1</version>
        </dependency>
        <!-- your json lib -->
        <dependency>
            <groupId>org.json</groupId>
            <artifactId>json</artifactId>
            <version>20141113</version>
        </dependency>
        <dependency>
            <groupId>org.xerial</groupId>
            <artifactId>sqlite-jdbc</artifactId>
            <version>3.8.7</version>
        </dependency>
        <dependency>
            <groupId>commons-fileupload</groupId>
            <artifactId>commons-fileupload</artifactId>
            <version>1.3.1</version>
        </dependency>
        <dependency>
            <groupId>commons-io</groupId>
            <artifactId>commons-io</artifactId>
            <version>2.4</version>
        </dependency>
    </dependencies>
    <build>
        <finalName>your app name</finalName>
        <plugins>
            <plugin>
                <artifactId>maven-war-plugin</artifactId>
                <version>2.4</version>
                <configuration>
                    <warSourceDirectory>WebContent</warSourceDirectory>
                    <failOnMissingWebXml>false</failOnMissingWebXml>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>