Chapter 1 Common EL expressions and chapter 1 el expressions

Chapter 1 Common EL expressions and chapter 1 el expressions

ElMost commonIn the following scenarios:

• Read attributes from the configuration file
• If the value is missing, configure the default value.
• El internal String use String method
• Three-object Operator
• Regular Expression
• System properties)
• Call Original system functions
• Direct file injection
• Read the return value of another bean Function

1. Read attributes from the configuration file

Application. properties

name=\u8D75\u8BA1\u521A

1 @ Value ("$ {name}") // $ must be used here. # is not applicable. 2 private String name; 3 @ RequestMapping (value = "/name ", method = RequestMethod. GET) 4 public String getName () {5 return name; 6}

Note: Remember the following two sentences.

• $ {} Reads the attribute file value
• $ {} Reads the last value that meets the condition; # {} reads all values that meet the condition.

2. If the value is missing, configure the default value.

1 @ Value ("$ {name2: 'hangzhou'}") // $ must be used here. #2 private String name2 is not supported; 3 @ RequestMapping (value = "/name2", method = RequestMethod. GET) 4 public String getName2 () {5 return name2; 6}

3. Use the String method for el internal strings

1 name.list=\u8D75\u8BA1\u521A,\u738B\u5A1C

1     @Value("#{'${name.list}'.split(',')}")2     private List<String> nameList;3     @RequestMapping(value = "/nameList", method = RequestMethod.GET)4     public List<String> getNameList() {5         return nameList;6     }

4. Three-object Operator

1 name.three=\u6768\u8FC7

1 @ RequestMapping (value = "/nameThree", method = RequestMethod. GET) 2 public String getNameThree (@ Value ("$ {name. three! = 'Yang Ta '? 'Yellow Rong ': 'Dragon female'} ") String nameThree) {3 return nameThree; 4}

Note: @ value can be directly used as an input parameter.

5. Regular Expression

1 @ Value ("# {'000000' matches '\ d +'}") // # is required here. 2 private boolean isDigital cannot be used with $; 3 @ RequestMapping (value = "/nameRegEx", method = RequestMethod. GET) 4 public boolean getNameRegEx () {5 return isDigital; 6}

6. Inject system attributes

1 @ Value ("# {systemProperties ['OS. name']} ") // # Must be used here. $ cannot be used. 2 private String osName; 3 @ RequestMapping (value ="/osName ", method = RequestMethod. GET) 4 public String getOsName () {5 return osName; 6}

7. Call Original system functions

1 @ Value ("# {T (java. lang. math ). random () * 10} ") // Note: This is generated only once. No matter how many times you call getRandomValue (), the same value 2 private String randomValue is returned; 3 @ RequestMapping (value = "/randomValue", method = RequestMethod. GET) 4 public String getRandomValue () {5 return randomValue; 6}

8. directly inject files for operations

Testfile/testEl.txt

1 Qiao Feng-jianglong 18 OPS 2 Yang Guo-suddenly lost the soul

 1     @Value("classpath:testfile/testEl.txt") 2     private Resource txtResource; 3     @RequestMapping(value = "/resource", method = RequestMethod.GET) 4     public String getResource() { 5         try { 6             return IOUtils.toString(txtResource.getInputStream(), "UTF-8"); 7         } catch (IOException e) { 8             ExceptionUtils.getStackTrace(e); 9         }10         return StringUtils.EMPTY;11     }

Note: This is very important. You can use Apache. commons. io. IOUtils to operate the operating file.

9. Read the return value of the function of another bean.

1 @ Component ("eLComponent") 2 public class ELComponent {3 public String getNameBean () {4 return "Qiao Feng"; 5} 6}

1 @ Value ("# {eLComponent. getNameBean ()} ") // # Must be used here. $ is not applicable to 2 private String nameBean; 3 @ RequestMapping (value ="/nameBean ", method = RequestMethod. GET) 4 public String getNameBean () {5 return nameBean; 6}

Note: it is best to specify beanName for the called bean.