当为空时获取空字符串

Use an inline null check

gearBox == null ? "" : String.valueOf(gearBox);

You can use Objects.toString() (standard in Java 7):

Objects.toString(gearBox, "")


Objects.toString(id, "")

From the linked documentation:

public static String toString(Object o, String nullDefault)

Returns the result of calling toString on the first argument if the first argument is not null and returns the second argument otherwise.

Parameters:
o - an object
nullDefault - string to return if the first argument is null

Returns:
the result of calling toString on the first argument if it is not null and the second argument otherwise.

See Also:
toString(Object)

If you don't mind using Apache commons, they have a StringUtils.defaultString(String str) that does this.

Returns either the passed in String, or if the String is null, an empty String ("").

If you also want to get rid of "null", you can do:

StringUtils.defaultString(str).replaceAll("^null$", "")

or to ignore case:

StringUtils.defaultString(str).replaceAll("^(?i)null$", "")

Since you're using guava:

Objects.firstNonNull(gearBox, "").toString();

For java 8 you can use Optional approach:

Optional.ofNullable(gearBox).orElse("");
Optional.ofNullable(id).orElse("");

If alternative way, Guava provides Strings.nullToEmpty(String).

Source code

String str = null;
str = Strings.nullToEmpty(str);
System.out.println("String length : " + str.length());

Result

0

In Java 9+ use : Objects.requireNonNullElse (obj, defaultObj) https://docs.oracle.com/javase/9/docs/api/java/util/Objects.html#requireNonNullElse-T-T-

//-- returns empty string if obj is null
Objects.requireNonNullElse (obj, "")

StringUtils.defaultString(String str) Returns either the passed in String, or if the String is null, an empty String ("").

Example from java doc

StringUtils.defaultString(null) will return "" StringUtils.defaultString("") will return "" StringUtils.defaultString("bat") will return "bat"