public abstract class CommandLinePropertySource<T> extends EnumerablePropertySource<T>
PropertySource implementations backed by command line
arguments. The parameterized type T represents the underlying source of command
line options. This may be as simple as a String array in the case of
SimpleCommandLinePropertySource, or specific to a particular API such as JOpt's
OptionSet in the case of JOptCommandLinePropertySource.
main method accepting a String[] of arguments from the
command line. In many cases, processing command-line arguments directly within the
main method may be sufficient, but in other cases, it may be desirable to
inject arguments as values into Spring beans. It is this latter set of cases in which
a CommandLinePropertySource becomes useful. A CommandLinePropertySource
will typically be added to the Environment of the Spring
ApplicationContext, at which point all command line arguments become available
through the PropertyResolver.getProperty(String) family of methods. For example:
public static void main(String[] args) {
CommandLinePropertySource clps = ...;
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
ctx.getEnvironment().getPropertySources().addFirst(clps);
ctx.register(AppConfig.class);
ctx.refresh();
}
With the bootstrap logic above, the AppConfig class may @Inject the
Spring Environment and query it directly for properties:
@Configuration
public class AppConfig {
@Inject Environment env;
@Bean
public void DataSource dataSource() {
MyVendorDataSource dataSource = new MyVendorDataSource();
dataSource.setHostname(env.getProperty("db.hostname", "localhost"));
dataSource.setUsername(env.getRequiredProperty("db.username"));
dataSource.setPassword(env.getRequiredProperty("db.password"));
// ...
return dataSource;
}
}
Because the CommandLinePropertySource was added to the Environment's
set of MutablePropertySources using the #addFirst method, it has
highest search precedence, meaning that while "db.hostname" and other properties may
exist in other property sources such as the system environment variables, it will be
chosen from the command line property source first. This is a reasonable approach
given that arguments specified on the command line are naturally more specific than
those specified as environment variables.
As an alternative to injecting the Environment, Spring's @Value
annotation may be used to inject these properties, given that a PropertySourcesPropertyResolver bean has been registered, either directly or through
using the <context:property-placeholder> element. For example:
@Component
public class MyComponent {
@Value("my.property:defaultVal")
private String myProperty;
public void getMyProperty() {
return this.myProperty;
}
// ...
}
Individual command line arguments are represented as properties through the usual
PropertySource.getProperty(String) and
PropertySource.containsProperty(String) methods. For example, given the
following command line:
--o1=v1 --o2'o1' and 'o2' are treated as "option arguments", and the following assertions would evaluate true:
CommandLinePropertySource ps = ...
assert ps.containsProperty("o1") == true;
assert ps.containsProperty("o2") == true;
assert ps.containsProperty("o3") == false;
assert ps.getProperty("o1").equals("v1");
assert ps.getProperty("o2").equals("");
assert ps.getProperty("o3") == null;
Note that the 'o2' option has no argument, but getProperty("o2") resolves to
empty string ("") as opposed to null, while getProperty("o3")
resolves to null because it was not specified. This behavior is consistent with
the general contract to be followed by all PropertySource implementations.
Note also that while "--" was used in the examples above to denote an option argument, this syntax may vary across individual command line argument libraries. For example, a JOpt- or Commons CLI-based implementation may allow for single dash ("-") "short" option arguments, etc.
Non-option arguments are also supported through this abstraction. Any arguments
supplied without an option-style prefix such as "-" or "--" are considered "non-option
arguments" and available through the special "nonOptionArgs" property. If multiple
non-option arguments are specified, the value of this property will be a
comma-delimited string containing all of the arguments. This approach ensures a simple
and consistent return type (String) for all properties from a CommandLinePropertySource and at the same time lends itself to conversion when used
in conjunction with the Spring Environment and its built-in ConversionService. Consider the following example:
--o1=v1 --o2=v2 /path/to/file1 /path/to/file2In this example, "o1" and "o2" would be considered "option arguments", while the two filesystem paths qualify as "non-option arguments". As such, the following assertions will evaluate true:
CommandLinePropertySource ps = ...
assert ps.containsProperty("o1") == true;
assert ps.containsProperty("o2") == true;
assert ps.containsProperty("nonOptionArgs") == true;
assert ps.getProperty("o1").equals("v1");
assert ps.getProperty("o2").equals("v2");
assert ps.getProperty("nonOptionArgs").equals("/path/to/file1,/path/to/file2");
As mentioned above, when used in conjunction with the Spring Environment
abstraction, this comma-delimited string may easily be converted to a String array or
list:
Environment env = applicationContext.getEnvironment();
String[] nonOptionArgs = env.getProperty("nonOptionArgs", String[].class);
assert nonOptionArgs[0].equals("/path/to/file1");
assert nonOptionArgs[1].equals("/path/to/file2");
The name of the special "non-option arguments" property may be customized through
the setNonOptionArgsPropertyName(String) method. Doing so is recommended as
it gives proper semantic value to non-option arguments. For example, if filesystem
paths are being specified as non-option arguments, it is likely preferable to refer to
these as something like "file.locations" than the default of "nonOptionArgs":
public static void main(String[] args) {
CommandLinePropertySource clps = ...;
clps.setNonOptionArgsPropertyName("file.locations");
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
ctx.getEnvironment().getPropertySources().addFirst(clps);
ctx.register(AppConfig.class);
ctx.refresh();
}
String[] of arguments
coming into the main method, and then simply providing the parsing results to an
implementation of CommandLinePropertySource. At that point, all arguments can
be considered either 'option' or 'non-option' arguments and as described above can be
accessed through the normal PropertySource and Environment APIs.PropertySource,
SimpleCommandLinePropertySource,
JOptCommandLinePropertySourcePropertySource.StubPropertySource| 限定符和类型 | 字段和说明 |
|---|---|
static String |
COMMAND_LINE_PROPERTY_SOURCE_NAME
The default name given to
CommandLinePropertySource instances: "commandLineArgs" |
static String |
DEFAULT_NON_OPTION_ARGS_PROPERTY_NAME
The default name of the property representing non-option arguments: "nonOptionArgs"
|
logger, name, source| 构造器和说明 |
|---|
CommandLinePropertySource(String name,
T source)
Create a new
CommandLinePropertySource having the given name
and backed by the given source object. |
CommandLinePropertySource(T source)
Create a new
CommandLinePropertySource having the default name
"commandLineArgs" and backed by the given source object. |
| 限定符和类型 | 方法和说明 |
|---|---|
protected abstract boolean |
containsOption(String name)
Return whether the set of option arguments parsed from the command line contains
an option with the given name.
|
boolean |
containsProperty(String name)
This implementation first checks to see if the name specified is the special
"non-option arguments" property,
and if so delegates to the abstract
getNonOptionArgs() method
checking to see whether it returns an empty collection. |
protected abstract List<String> |
getNonOptionArgs()
Return the collection of non-option arguments parsed from the command line.
|
protected abstract List<String> |
getOptionValues(String name)
Return the collection of values associated with the command line option having the
given name.
|
String |
getProperty(String name)
This implementation first checks to see if the name specified is the special
"non-option arguments" property,
and if so delegates to the abstract
getNonOptionArgs() method. |
void |
setNonOptionArgsPropertyName(String nonOptionArgsPropertyName)
Specify the name of the special "non-option arguments" property.
|
getPropertyNamespublic static final String COMMAND_LINE_PROPERTY_SOURCE_NAME
CommandLinePropertySource instances: "commandLineArgs"public CommandLinePropertySource(T source)
CommandLinePropertySource having the default name
"commandLineArgs" and backed by the given source object.public CommandLinePropertySource(String name, T source)
CommandLinePropertySource having the given name
and backed by the given source object.public void setNonOptionArgsPropertyName(String nonOptionArgsPropertyName)
public final boolean containsProperty(String name)
getNonOptionArgs() method
checking to see whether it returns an empty collection. Otherwise delegates to and
returns the value of the abstract containsOption(String) method.containsProperty 在类中 EnumerablePropertySource<T>name - the name of the property to find@Nullable public final String getProperty(String name)
getNonOptionArgs() method. If so
and the collection of non-option arguments is empty, this method returns null. If not empty, it returns a comma-separated String of all non-option
arguments. Otherwise delegates to and returns the result of the abstract getOptionValues(String) method.getProperty 在类中 PropertySource<T>name - the property to findPropertyResolver.getRequiredProperty(String)protected abstract boolean containsOption(String name)
@Nullable protected abstract List<String> getOptionValues(String name)
[])["bar"])["bar", "baz"])null