watch

Monitor the methods in data aspect including return value, exceptions and parameters.

With the help of OGNL, you can easily check the details of the variables.

Parameters & Options

There are four different usage scenarios for watch command, which makes it the most complicated command in Arthas.

Name Specification
class-pattern pattern for the class name
method-pattern pattern for the method name
express expression to monitor
condition-express condition expression
[b] before invoking
[e] encountering exceptions
[s] returned normally
[f] returned normally and abnormally
[E] turn on regx matching while the default is wildcards matching
[x:] the depth to print the specified property with default value: 1

F.Y.I

  1. any valid OGNL expression as "{params,returnObj}" supported
  2. there are four watching points: -b, -e, -s and -f (the first three are off in default while -f on);
  3. at the watching point, Arthas will use the expression to calculate the values and print them out;
  4. in-parameters and out-parameters are different since they can be modified; params stands for in-parameters in -bwhile out-parameters in other watching points;
  5. there is no return value and exceptions when using -b.

Advanced:

Usage

A demo:

    public void execute() {
        List<String> list = new ArrayList<String>();
        list.add("a");
        list.add("b");

        List<String> list2 = new ArrayList<String>();
        list2.add("c");
        list2.add("d");

        int len = add(list, list2);
    }

    private static int add(List<String> list, List<String> list2) {
        list.addAll(list2);
        return list.size();
    }

Check the out-parametersand return value

$ watch com.alibaba.sample.petstore.web.store.module.screen.ItemList add "{params,returnObj}" -x 2
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 44 ms.
@ArrayList[
    @Object[][
        @ArrayList[isEmpty=false;size=4],
        @ArrayList[isEmpty=false;size=2],
    ],

    @Integer[4],
]

Check in-parameters

$ watch com.alibaba.sample.petstore.web.store.module.screen.ItemList add "{params,returnObj}" -x 2 -b
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 48 ms.  
@ArrayList[
    @Object[][
        @ArrayList[isEmpty=false;size=2],
        @ArrayList[isEmpty=false;size=2],
    ],

    null,
]

Compared to the previous check:

  1. size of params[0] is 2 instead of 4;
  2. return value is null since it’s -b.

Check before and after at the same time

$ watch com.alibaba.sample.petstore.web.store.module.screen.ItemList add "{params,returnObj}" -x 2 -b -s 
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 59 ms.  
@ArrayList[
    @Object[][
        @ArrayList[isEmpty=false;size=2],
        @ArrayList[isEmpty=false;size=2],
    ],

    null,
]
@ArrayList[
    @Object[][
        @ArrayList[isEmpty=false;size=4],
        @ArrayList[isEmpty=false;size=2],
    ],

    @Integer[4],
]

F.Y.I

  1. the first block of output is the before watching point;
  2. the order of the output determined by the watching order itself (nothing to do with the order of the options -b -s).

Using -x to check more details

$ watch com.alibaba.sample.petstore.web.store.module.screen.ItemList add "{params,returnObj}" -x 3 
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 59 ms.  
@ArrayList[
    @Object[][
        @ArrayList[
            @String[a],

            @String[b],

            @String[c],

            @String[d],
        ],
        @ArrayList[
            @String[c],

            @String[d],
        ],
    ],

    @Integer[4],
]

Using condition expressions to locate specific call

$ watch com.alibaba.sample.petstore.biz.impl.UserManagerImpl testAdd "{params, returnObj}" "params[0].equals('aaa')" -x 2 
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 29 ms.  
@ArrayList[
    @Object[][
        @String[aaa],
        @String[bbb],
    ],

    @Integer[6],
]

Check exceptions

$ watch com.alibaba.sample.petstore.biz.impl.UserManagerImpl testAdd "{params, throwExp}"  -e -x 2 
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 29 ms.  
@ArrayList[
    @Object[][
        @String[aaa],
        @String[bbb],
    ],

    java.lang.NullPointerException
        at com.alibaba.sample.petstore.biz.impl.UserManagerImpl.testAdd(UserManagerImpl.java:75)
        at com.alibaba.sample.petstore.biz.impl.UserManagerImpl.register(UserManagerImpl.java:60)
        at com.alibaba.sample.petstore.web.user.module.action.RegisterAction.doRegister(RegisterAction.java:45)
        at com.alibaba.sample.petstore.web.user.module.action.RegisterAction$$FastClassByCGLIB$$ad5428f1.invoke(<generated>)
        at net.sf.cglib.reflect.FastMethod.invoke(FastMethod.java:53)
        at com.alibaba.citrus.service.moduleloader.impl.adapter.MethodInvoker.invoke(MethodInvoker.java:70)
        at com.alibaba.citrus.service.moduleloader.impl.adapter.AbstractModuleEventAdapter.executeAndReturn(AbstractModuleEventAdapter.java:100)
        at com.alibaba.citrus.service.moduleloader.impl.adapter.AbstractModuleEventAdapter.execute(AbstractModuleEventAdapter.java:58)
        at com.alibaba.citrus.turbine.pipeline.valve.PerformActionValve.invoke(PerformActionValve.java:63)
        at com.alibaba.citrus.service.pipeline.impl.PipelineImpl$PipelineContextImpl.invokeNext(PipelineImpl.java:157)
        at com.alibaba.citrus.service.pipeline.impl.PipelineImpl$PipelineContextImpl.invoke(PipelineImpl.java:210)
        at com.alibaba.citrus.service.pipeline.impl.valve.ChooseValve.invoke(ChooseValve.java:98)
        at com.alibaba.citrus.service.pipeline.impl.PipelineImpl$PipelineContextImpl.invokeNext(PipelineImpl.java:157)
        at com.alibaba.citrus.service.pipeline.impl.PipelineImpl$PipelineContextImpl.invoke(PipelineImpl.java:210)
        at com.alibaba.citrus.service.pipeline.impl.valve.LoopValve.invokeBody(LoopValve.java:105)
        at com.alibaba.citrus.service.pipeline.impl.valve.LoopValve.invoke(LoopValve.java:83)
        at com.alibaba.citrus.service.pipeline.impl.PipelineImpl$PipelineContextImpl.invokeNext(PipelineImpl.java:157)
        at com.alibaba.citrus.turbine.pipeline.valve.PageAuthorizationValve.invoke(PageAuthorizationValve.java:105)
        at com.alibaba.citrus.service.pipeline.impl.PipelineImpl$PipelineContextImpl.invokeNext(PipelineImpl.java:157)
        at com.alibaba.citrus.turbine.pipeline.valve.CheckCsrfTokenValve.invoke(CheckCsrfTokenValve.java:123)
        at com.alibaba.citrus.service.pipeline.impl.PipelineImpl$PipelineContextImpl.invokeNext(PipelineImpl.java:157)
        at com.alibaba.citrus.turbine.pipeline.valve.AnalyzeURLValve.invoke(AnalyzeURLValve.java:126)
        at com.alibaba.citrus.service.pipeline.impl.PipelineImpl$PipelineContextImpl.invokeNext(PipelineImpl.java:157)
        at com.alibaba.citrus.turbine.pipeline.valve.SetLoggingContextValve.invoke(SetLoggingContextValve.java:66)
        at com.alibaba.citrus.service.pipeline.impl.PipelineImpl$PipelineContextImpl.invokeNext(PipelineImpl.java:157)
        at com.alibaba.citrus.turbine.pipeline.valve.PrepareForTurbineValve.invoke(PrepareForTurbineValve.java:52)
        at com.alibaba.citrus.service.pipeline.impl.PipelineImpl$PipelineContextImpl.invokeNext(PipelineImpl.java:157)
        at com.alibaba.citrus.service.pipeline.impl.PipelineImpl$PipelineContextImpl.invoke(PipelineImpl.java:210)
        at com.alibaba.citrus.webx.impl.WebxControllerImpl.service(WebxControllerImpl.java:43)
        at com.alibaba.citrus.webx.impl.WebxRootControllerImpl.handleRequest(WebxRootControllerImpl.java:53)
        at com.alibaba.citrus.webx.support.AbstractWebxRootController.service(AbstractWebxRootController.java:165)
        at com.alibaba.citrus.webx.servlet.WebxFrameworkFilter.doFilter(WebxFrameworkFilter.java:152)
        at com.alibaba.citrus.webx.servlet.FilterBean.doFilter(FilterBean.java:148)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
        at com.alibaba.citrus.webx.servlet.SetLoggingContextFilter.doFilter(SetLoggingContextFilter.java:61)
        at com.alibaba.citrus.webx.servlet.FilterBean.doFilter(FilterBean.java:148)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
        at com.taobao.tomcat.valves.ContextLoadFilterValve.invoke(ContextLoadFilterValve.java:152)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:429)
        at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1085)
        at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:625)
        at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1760)
        at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1719)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
        at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
        at java.lang.Thread.run(Thread.java:745),
]

Filter based on time cost

$ watch com.alibaba.sample.petstore.web.store.module.screen.ItemList add "{params,returnObj}" #cost>200 -x 3 
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 59 ms.  
@ArrayList[
    @Object[][
        @ArrayList[
            @String[a],

            @String[b],

            @String[c],

            @String[d],
        ],
        @ArrayList[
            @String[c],

            @String[d],
        ],
    ],

    @Integer[4],
]

F.Y.I #cost>200 (ms) filter out all invokings that take less than 200ms.

Check the global properties of the target object

target stands for the current object.

$ watch com.taobao.container.web.arthas.rest.MyAppsController myFavoriteApps 'target'
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 128 ms.
ts=2017-10-31 18:45:55;result=@MyAppsController[
    myFavAppsMapper=@$Proxy131[org.apache.ibatis.binding.MapperProxy@563e97f3],
    getAppNameAndIdByEmpId=@$Proxy135[HardCodedTarget(type=GetAppNameAndIdByEmpId, url=http://hello.com)],
    enableWebConsoleAppsMapper=@$Proxy132[org.apache.ibatis.binding.MapperProxy@7d51e4a8],
]

target.field_name stands for a global property of the current object.

$ watch com.taobao.container.web.arthas.rest.MyAppsController myFavoriteApps 'target.myFavAppsMapper'
Press Ctrl+C to abort.
Affect(class-cnt:1 , method-cnt:1) cost in 126 ms.
ts=2017-10-31 18:46:17;result=@$Proxy131[
    m1=@Method[public boolean java.lang.Object.equals(java.lang.Object)],
    m2=@Method[public java.lang.String java.lang.Object.toString()],
    m5=@Method[public abstract java.util.List com.taobao.container.dal.arthas.mapper.MyFavAppsMapper.listFavApps(java.util.Map)],
    m3=@Method[public abstract int com.taobao.container.dal.arthas.mapper.MyFavAppsMapper.delete(java.lang.String,java.lang.String,java.lang.String)],
    m4=@Method[public abstract long com.taobao.container.dal.arthas.mapper.MyFavAppsMapper.insert(com.taobao.container.dal.arthas.domain.MyFavAppsDO)],
    m0=@Method[public native int java.lang.Object.hashCode()],
]