Use Arthas to locate online problems

background ： There is an export PDF The function of , It works well locally , Online exception , The exception thrown cannot directly locate the problem .

1、 Use arthas To keep track of

1. Get into arths,attach Entry project

$ as.sh
Arthas script version: 3.5.5
[INFO] JAVA_HOME: /usr/local/jdk1.8.0_72
[INFO] Process 57135 already using port 3658
[INFO] Process 57135 already using port 8563
Found existing java process, please choose one and input the serial number of the process, eg : 1. Then hit ENTER.
  [1]: 134242 ccs-gateway.jar
  [2]: 47802 ccs-data-biz.jar
2

2. According to online log Locate the approximate location of the anomaly

3. To local IDE Open source

createPDF Method null pointer , The first thing you must think of is parameters htmlStr yes null

4. Get into freemarkerRender Method view , Why go back null

5. Directly view the key processing functions template.process(dataMap, out);

6. Use arthas Of watch command , Tracking parameters 、 Return value 、 Abnormal information

watch freemarker.template.Template process '{params,returnObj,throwExp}'  -n 5  -x 3 '1==1'

Tracking findings

7. Capture is not specified in the source code because of exceptions TemplateModelException therefore template.process(dataMap, out); The method returns directly after reporting an error null, So change the exception capture directly to ExcelpTion that will do