Apache Camel框架入门示例

Apache Camel是Apache基金会下的一个开源项目,它是一个基于规则路由和处理的引擎，提供企业集成模式的Java对象的实现，通过应用程序接口 或称为陈述式的Java领域特定语言(DSL)来配置路由和处理的规则。其核心的思想就是从一个from源头得到数据,通过processor处理,再发到一个to目的的.
这个from和to可以是我们在项目集成中经常碰到的类型:一个FTP文件夹中的文件,一个MQ的queue,一个HTTP request/response,一个webservice等等.
Camel可以很容易集成到standalone的应用,在容器中运行的Web应用,以及和Spring一起集成.
下面用一个示例,介绍怎么开发一个最简单的Camel应用.
1,从http://camel.apache.org/download.html下载Jar包.在本文写作的时候最新版本是2.9. 本文用的是2.7,从2.7开始要求需要JRE1.6的环境.
下载的zip包含了Camel各种特性要用到的jar包.
在本文入门示例用到的Jar包只需要:camel-core-2.7.5.jar,commons-management-1.0.jar,slf4j-api-1.6.1.jar.
2,新建一个Eclipse工程,将上面列出的jar包设定到工程的Classpath.
新建一个如下的类:运行后完成的工作是将d:/temp/inbox/下的所有文件移到d:/temp/outbox

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1. public class FileMoveWithCamel {
2. public static void main(String args[]) throws Exception {
3. CamelContext context = new DefaultCamelContext();
4. context.addRoutes(new RouteBuilder() {
5. public void configure() {
6. //from("file:d:/temp/inbox?noop=true").to("file:d:/temp/outbox");
7. from("file:d:/temp/inbox/?delay=30000").to("file:d:/temp/outbox");
8. }
9. });
10. context.start();
11. boolean loop =true;
12. while(loop){
13. Thread.sleep(25000);
14. }
15. context.stop();
16. }
17. }

public class FileMoveWithCamel {    public static void main(String args[]) throws Exception {        CamelContext context = new DefaultCamelContext();        context.addRoutes(new RouteBuilder() {        public void configure() {        //from("file:d:/temp/inbox?noop=true").to("file:d:/temp/outbox");         from("file:d:/temp/inbox/?delay=30000").to("file:d:/temp/outbox");        }        });        context.start();        boolean loop =true;        while(loop){            Thread.sleep(25000);        }                context.stop();        }}

上面的例子体现了一个最简单的路由功能,比如d:/temp/inbox/是某一个系统FTP到Camel所在的系统的一个接收目录.
d:/temp/outbox为Camel要发送的另一个系统的接收目录.
from/to可以是如下别的形式,读者是否可以看出Camel是可以用于系统集成中做路由,流程控制一个非常好的框架了呢?
from("file:d:/temp/inbox/?delay=30000").to("jms:queue:order");//delay=30000是每隔30秒轮询一次文件夹中是否有文件.
3,再给出一个从from到to有中间流程process处理的例子:

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1. public class FileProcessWithCamel {
2. public static void main(String args[]) throws Exception {
3. CamelContext context = new DefaultCamelContext();
4. context.addRoutes(new RouteBuilder() {
6. public void configure() {
7. FileConvertProcessor processor = new FileConvertProcessor();
8. from("file:d:/temp/inbox?noop=true").process(processor).to("file:d:/temp/outbox");
9. }
10. });
12. context.start();
13. boolean loop =true;
14. while(loop){
15. Thread.sleep(25000);
16. }
17. context.stop();
18. }
19. }

public class FileProcessWithCamel {    public static void main(String args[]) throws Exception {        CamelContext context = new DefaultCamelContext();            context.addRoutes(new RouteBuilder() {                    public void configure() {        FileConvertProcessor processor = new FileConvertProcessor();        from("file:d:/temp/inbox?noop=true").process(processor).to("file:d:/temp/outbox");        }        });                context.start();        boolean loop =true;        while(loop){            Thread.sleep(25000);        }        context.stop();        }}

这里的处理只是简单的把接收到的文件多行转成一行

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1. public class FileConvertProcessorimplements Processor{
2. @Override
3. public void process(Exchange exchange)throws Exception {
4. try {
5. InputStream body = exchange.getIn().getBody(InputStream.class);
6. BufferedReader in = new BufferedReader(new InputStreamReader(body));
7. StringBuffer strbf = new StringBuffer("");
8. String str = null;
9. str = in.readLine();
10. while (str != null) {
11. System.out.println(str);
12. strbf.append(str + " ");
13. str = in.readLine();
14. }
15. exchange.getOut().setHeader(Exchange.FILE_NAME, "converted.txt");
16. // set the output to the file
17. exchange.getOut().setBody(strbf.toString());
18. } catch (IOException e) {
19. e.printStackTrace();
20. }
21. }
22. }

public class FileConvertProcessor implements Processor{    @Override    public void process(Exchange exchange) throws Exception {            try {            InputStream body = exchange.getIn().getBody(InputStream.class);            BufferedReader in = new BufferedReader(new InputStreamReader(body));            StringBuffer strbf = new StringBuffer("");            String str = null;            str = in.readLine();            while (str != null) {                                System.out.println(str);                strbf.append(str + " ");                str = in.readLine();                            }            exchange.getOut().setHeader(Exchange.FILE_NAME, "converted.txt");            // set the output to the file            exchange.getOut().setBody(strbf.toString());        } catch (IOException e) {            e.printStackTrace();        }    }}

在Eclipse里运行的时候,Camel默认不会把log信息打印到控制台,这样出错的话，异常是看不到的,需要把log4j配置到项目中.

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1. log4j.appender.stdout = org.apache.log4j.ConsoleAppender
2. log4j.appender.stdout.Target = System.out
3. log4j.appender.stdout.layout = org.apache.log4j.PatternLayout
4. log4j.appender.stdout.layout.ConversionPattern = %-5p %d [%t] %c: %m%n
5. log4j.rootLogger = debug,stdout