JSON-RPC

服务端开发，在很多情况下，需要使用到RPC框架，今天发现一款很轻量的RPC框架——JSON-RPC。json rpc 是一种以json为消息格式的远程调用服务，它是一套允许运行在不同操作系统、不同环境的程序实现基于Internet过程调用的规范和一系列的实现。这种远程过程调用可以使用http作为传输协议，也可以使用其它传输协议，传输的内容是json消息体。
json rpc 和xmlrpc相比具有很多优点。首先xmlrpc是以xml作为消息格式，xml具有体积大，格式复杂，传输占用带宽。程序对xml的解析也比较复杂，并且耗费较多服务器资源。json相比xml体积小巧，并且解析相对容易很多。
json-rpc是一种非常轻量级的跨语言远程调用协议，实现及使用简单。仅需几十行代码，即可实现一个远程调用的客户端，方便语言扩展客户端的实现。服务器端有php、java、python、ruby、.net等语言实现，是非常不错的及轻量级的远程调用协议。
其官网地址是：http://www.jsonrpc.org/
其Wiki地址是：http://json-rpc.org/wiki/implementations
可以看到，JSON-RPC有C，C++，C#，Javascipt，Erlang，Objective-C，Java等多种语言的实现，这里我简单介绍下Java使用JSON-RPC的示例，今天折腾了半天弄得。
首先就是要下载jsonrpc4j的jar包以及其依赖的jar包，这里我直接搭建Maven项目，使用Maven来管理jar包，其pom文件如下：

pom.xml

<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/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.hjc.demo</groupId>
    <artifactId>jsonrpc_server</artifactId>
    <packaging>war</packaging>
    <version>0.0.1-SNAPSHOT</version>
    <name>jsonrpc_server Maven Webapp</name>
    <url>http://maven.apache.org</url>
    <dependencies>
        <!-- jsonrpc4j -->
        <dependency>
            <groupId>com.github.briandilley.jsonrpc4j</groupId>
            <artifactId>jsonrpc4j</artifactId>
            <version>1.0</version>
        </dependency>
        <!-- jsonrpc4j依赖的包 -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.10</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version>2.0.2</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.0.2</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-annotations</artifactId>
            <version>2.0.2</version>
        </dependency>
        <dependency>
            <groupId>javax.portlet</groupId>
            <artifactId>portlet-api</artifactId>
            <version>2.0</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>3.1.2.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>3.1.2.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-web</artifactId>
            <version>3.1.2.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
            <version>3.1.2.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>commons-codec</groupId>
            <artifactId>commons-codec</artifactId>
            <version>1.4</version>
        </dependency>
        <dependency>
            <groupId>org.apache.httpcomponents</groupId>
            <artifactId>httpcore-nio</artifactId>
            <version>4.2.1</version>
        </dependency>
        <dependency>
            <groupId>org.jmock</groupId>
            <artifactId>jmock-junit4</artifactId>
            <version>2.5.1</version>
        </dependency>
        <dependency>
            <groupId>org.jmock</groupId>
            <artifactId>jmock</artifactId>
            <version>2.5.1</version>
        </dependency>
        <dependency>
            <groupId>org.eclipse.jetty</groupId>
            <artifactId>jetty-server</artifactId>
            <version>9.0.0.RC0</version>
        </dependency>
        <dependency>
            <groupId>org.eclipse.jetty</groupId>
            <artifactId>jetty-servlet</artifactId>
            <version>9.0.0.RC0</version>
        </dependency>
        <dependency>
            <groupId>org.ow2.chameleon.fuchsia.base.json-rpc</groupId>
            <artifactId>org.ow2.chameleon.fuchsia.base.json-rpc.json-rpc-bundle</artifactId>
            <version>0.0.2</version>
        </dependency>

    </dependencies>
    <build>
        <finalName>jsonrpc_server</finalName>
    </build>
</project>

待以上jar包等环境部署好了之后，就可以进行开发了，我们先要部署一个Servlet，作为RPC调用的接口。（我的环境的Tomcat6，Tomcat7的朋友可以直接使用@WebServlet来部署Servlet，具体代码因环境而异）。

web.xml

<!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>
  <display-name>Archetype Created Web Application</display-name>
  <servlet>
    <servlet-name>RpcServer</servlet-name>
    <display-name>RpcServer</display-name>
    <description></description>
    <servlet-class>com.hjc.demo.RpcServer</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>RpcServer</servlet-name>
    <url-pattern>/rpc</url-pattern>
  </servlet-mapping>
</web-app>

RpcServer.java

package com.hjc.demo;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.googlecode.jsonrpc4j.JsonRpcServer;

public class RpcServer extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private JsonRpcServer rpcServer = null;

    public RpcServer() {
        super();
        rpcServer = new JsonRpcServer(new DemoServiceImply(), DemoService.class);
    }

    @Override
    protected void service(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        rpcServer.handle(request, response);
    }

}

其中，DemoService是RPC调用的接口，DemoServiceImply是DemoService接口的实现，他们的代码分别如下：

DemoService.java

package com.hjc.demo;

public interface DemoService {

    public DemoBean getDemo(String code, String msg);

    public Integer getInt(Integer code);

    public String getString(String msg);

    public void doSomething();
}

DemoServiceImply.java

package com.hjc.demo;

public class DemoServiceImply implements DemoService {

    public DemoBean getDemo(String code, String msg) {
        DemoBean bean1 = new DemoBean();
        bean1.setCode(Integer.parseInt(code));
        bean1.setMsg(msg);
        return bean1;
    }

    public Integer getInt(Integer code) {
        return code;
    }

    public String getString(String msg) {
        return msg;
    }

    public void doSomething() {
        System.out.println("do something");
    }

}

DemoBean是一个普通的JavaBean，其代码如下：

DemoBean.java

package com.hjc.demo;

import java.io.Serializable;

public class DemoBean implements Serializable{
    private static final long serialVersionUID = -5141784402935371524L;
    private int code;
    private String msg;

    public int getCode() {
        return code;
    }

    public void setCode(int code) {
        this.code = code;
    }

    public String getMsg() {
        return msg;
    }

    public void setMsg(String msg) {
        this.msg = msg;
    }
}

以上代码即完成了服务端的代码，接下来写一个客户端的测试类：

JsonRpcTest.java

package com.hjc.test;

import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import com.fasterxml.jackson.databind.node.ObjectNode;
import com.googlecode.jsonrpc4j.JsonRpcHttpClient;
import com.hjc.demo.DemoBean;

public class JsonRpcTest {
    static JsonRpcHttpClient client;

    public JsonRpcTest() {

    }

    public static void main(String[] args) throws Throwable {
        // 实例化请求地址，注意服务端web.xml中地址的配置
        try {
            client = new JsonRpcHttpClient(new URL(
                    "http://127.0.0.1:8080/jsonrpc_server/rpc"));
            // 请求头中添加的信息
            Map<String, String> headers = new HashMap<String, String>();
            headers.put("UserKey", "hjckey");
            // 添加到请求头中去
            client.setHeaders(headers);
            JsonRpcTest test = new JsonRpcTest();
            test.doSomething();
            DemoBean demo = test.getDemo(1, "哈");
            int code = test.getInt(2);
            String msg = test.getString("哈哈哈");
            // print
            System.out.println("===========================javabean");
            System.out.println(demo.getCode());
            System.out.println(demo.getMsg());
            System.out.println("===========================Integer");
            System.out.println(code);
            System.out.println("===========================String");
            System.out.println(msg);
            System.out.println("===========================end");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void doSomething() throws Throwable {
        client.invoke("doSomething", null);
    }

    public DemoBean getDemo(int code, String msg) throws Throwable {
        String[] params = new String[] { String.valueOf(code), msg };
        DemoBean demo = null;
        demo = client.invoke("getDemo", params, DemoBean.class);
        return demo;
    }

    public int getInt(int code) throws Throwable {
        Integer[] codes = new Integer[] { code };
        return client.invoke("getInt", codes, Integer.class);
    }

    public String getString(String msg) throws Throwable {
        String[] msgs = new String[] { msg };
        return client.invoke("getString", msgs, String.class);
    }

}

最后的打印结果如下：

服务端：

do something

客户端：

===========================javabean
1
哈
===========================Integer
2
===========================String
哈哈哈
===========================end

以上就完成了JSON-RPC全部的代码，值得说的是，这其中我也爬了很多坑，这里也提一下，JsonRpcHttpClient类的invoke方法，如果你要传递参数，必须是一个数组，这里我传的String[]和Integer[]，如果传递了别的类型会发生什么呢？你可以试一下这样调用：

client.invoke("getInt", 3, Integer.class);

然后你就会发现服务端报错：

java.lang.IllegalArgumentException: Unknown params node type: 2
    at com.googlecode.jsonrpc4j.JsonRpcServer.findBestMethodByParamsNode(JsonRpcServer.java:612)
    at com.googlecode.jsonrpc4j.JsonRpcServer.handleObject(JsonRpcServer.java:373)
    at com.googlecode.jsonrpc4j.JsonRpcServer.handleNode(JsonRpcServer.java:293)
    at com.googlecode.jsonrpc4j.JsonRpcServer.handle(JsonRpcServer.java:230)
    at com.googlecode.jsonrpc4j.JsonRpcServer.handle(JsonRpcServer.java:207)
    at com.hjc.demo.RpcServer.service(RpcServer.java:24)
        ...

点进源码，你就全明白了，进入JsonRpcServer类查看findBestMethodByParamsNode方法，其代码如下：

/**
     * Finds the {@link Method} from the supplied {@link Set} that
     * best matches the rest of the arguments supplied and returns
     * it as a {@link MethodAndArgs} class.
     *
     * @param methods the {@link Method}s
     * @param paramsNode the {@link JsonNode} passed as the parameters
     * @return the {@link MethodAndArgs}
     */
    private MethodAndArgs findBestMethodByParamsNode(Set<Method> methods, JsonNode paramsNode) {

        // no parameters
        if (paramsNode==null || paramsNode.isNull()) {
            return findBestMethodUsingParamIndexes(methods, 0, null);

        // array parameters
        } else if (paramsNode.isArray()) {
            return findBestMethodUsingParamIndexes(methods, paramsNode.size(), ArrayNode.class.cast(paramsNode));

        // named parameters
        } else if (paramsNode.isObject()) {
            Set<String> fieldNames = new HashSet<String>();
            Iterator<String> itr=paramsNode.fieldNames();
            while (itr.hasNext()) {
                fieldNames.add(itr.next());
            }
            return findBestMethodUsingParamNames(methods, fieldNames, ObjectNode.class.cast(paramsNode));

        }

        // unknown params node type
        throw new IllegalArgumentException("Unknown params node type: "+paramsNode.toString());
    }

所以我就明白了，除了null（不传参数），Array，Object，其他的类都是“Unknown params node type”，当时我也很疑惑，Integer不也是Object嘛，断点一下，原来它认为这是IntNode类，所以不能识别，其他的参数我也试过一些，目前还是数组是最靠谱的，网上资料还比较少，希望有懂得给指点指点。
这也是我今天花了半天时间弄得JSON-RPC，喜欢的朋友，源码地址在下面：
https://github.com/hjcenry/json-rpc-demo