Java 避免重复构建字符串的最佳方法

我有一个硬编码的字符串，将在URL中使用，我想知道构建这个字符串的最佳方法是什么，而不必重复单词

country，或，and，number

？这是一个简短的版本，因为有更多的国家和数字将进入URL

String url = "&filter=country='UK' or "
                      + "country='FR' or "
                      + "country='CA' or "
                      + "country='US' and "
                      + "number='123' and "
                      + "number='789'";

---

我建议您创建数组来保存每个差异，并将它们附加到for循环中：

String[] countries = {"'UK' or ", "'FR' or ", "'CA' or ", "'US' and "};

String[] numbers = {"'123' and ", "'789'"};

StringBuilder sb = new StringBuilder("&filter=");

for (String country : countries) {
    sb.append("country=").append(country);
}

for (String number : numbers) {
    sb.append("number=").append(number);
}

String url = sb.toString();

---

您可以使用

StringBuilder

和

String

格式的组合来构建特定的URL参数化

下面是一个例子：

// test data
List<String> countries = Arrays.asList("UK", "FR","CA", "US");
List<String> numbers = Arrays.asList("123", "789");

// these can be compile-time constants
String disjunct  = " or ";
String conjunct = " and ";
String countryFormat = "country='%s'";
String numberFormat = "number='%s'";

// result 
StringBuilder result = new StringBuilder("&filter=");

// adding countries
for (String country: countries) {
    result.append(String.format(countryFormat, country)).append(disjunct);
}
// removing last "or"
result.delete(result.lastIndexOf(disjunct), result.length());

// adding first "and"
result.append(conjunct);

// adding numbers
for (String number: numbers) {
    result.append(String.format(numberFormat, number)).append(conjunct);
}
// removing last "and"
result.delete(result.lastIndexOf(conjunct), result.length());

// printing result
System.out.println(result);

---

您还可以创建一个帮助器类来为您构建字符串

public class Test {
private Test() {

    // each country for its own
    IFilterBuilder filterBuilder = new FilterBuilder();
    filterBuilder
            .country("UK").or()
            .country("FR").or()
            .country("CA").or()
            .country("US").and()
            .number(123).and()
            .number(789);

    String myFilter = filterBuilder.getResult();
    System.out.println(myFilter);


    // or a short version with a helper method
    IFilterBuilder smartFilterBuilder = new FilterBuilder();
    smartFilterBuilder.inAnyCountry("UK", "FR", "CA", "US").and().withNumbers(123, 789);

    String result = smartFilterBuilder.getResult();
    System.out.println(result);
}

public static void main(String[] args) {
    new Test();
}

interface IFilterBuilderBinder {
    IFilterBuilder or();
    IFilterBuilder and();
}

interface IFilterBuilder {
    IFilterBuilderBinder country(String countryName);
    IFilterBuilderBinder number(int number);
    String getResult();

    IFilterBuilderBinder inAnyCountry(String... country);
    IFilterBuilderBinder withNumbers(int... numbers);
}

private final static class FilterBuilder implements IFilterBuilder, IFilterBuilderBinder {
    private String filter = "&filter=";

    public IFilterBuilderBinder country(String countryName) {
        filter += "country='" + countryName + "'";
        return this;
    }

    @Override
    public IFilterBuilderBinder number(int number) {
        filter += "number='" + number + "'";
        return this;
    }

    public String getResult() {
        return filter;
    }

    @Override
    public IFilterBuilderBinder inAnyCountry(String... country) {
        for (int i = 0; i < country.length; i++) {
            country( country[i]);
            if(i!=country.length-1){
                or();
            }
        }
        return this;
    }

    @Override
    public IFilterBuilderBinder withNumbers(int... numbers) {
        for (int i = 0; i < numbers.length; i++) {
            number(numbers[i]);
            if(i!=numbers.length-1){
                and();
            }
        }
        return this;
    }

    @Override
    public IFilterBuilder or() {
        filter += " or ";
        return this;
    }

    @Override
    public IFilterBuilder and() {
        filter += " and ";
        return this;
    }
}

公共类测试{
私人测试（）{
//每个国家都有自己的利益
IFilterBuilder filterBuilder=新的filterBuilder（）；
过滤器生成器
.国家（“英国”）。或（）
.国家（“FR”）。或（）
.国家（“CA”）。或（）
.国家（“美国”）和（）
.编号（123）。及（）
.电话号码（789）；
字符串myFilter=filterBuilder.getResult（）；
System.out.println（myFilter）；
//或者是带有帮助器方法的简短版本
IFilterBuilder smartFilterBuilder=新的FilterBuilder（）；
smartFilterBuilder。位于任何国家（“英国”、“法国”、“加利福尼亚”、“美国”）。和（）；
字符串结果=smartFilterBuilder.getResult（）；
系统输出打印项次（结果）；
}
公共静态void main（字符串[]args）{
新测试（）；
}
接口IFilterBuilderBinder{
IFilterBuilder或（）；
IFilterBuilder和（）；
}
界面过滤器生成器{
IFilterBuilderBinder国家（字符串countryName）；
IFilterBuilderBinder编号（整数）；
字符串getResult（）；
IFilterBuilderBinder位于任何国家（字符串…国家/地区）；
IFilterBuilderBinder带数字（整数…数字）；
}
私有最终静态类FilterBuilder实现IFilterBuilder、IFilterBuilder和IFilterBuilderBinder{
私有字符串筛选器=“&filter=”；
公共IFilterBuilderBinder国家（字符串countryName）{
过滤器+=“国家=”+“国家名+”；
归还这个；
}
@凌驾
公共IFilterBuilderBinder编号（整数）{
过滤器+=“数字=”+“数字+”；
归还这个；
}
公共字符串getResult（）{
回流过滤器；
}
@凌驾
国家/地区的公共IFilterBuilderBinder（字符串…国家/地区）{
对于（int i=0；i

---

}

首先使用

StringBuilder

类，其次，如果不想重复关键字，您可以使用常量。您也可以使用一些众所周知的Java HTTP库来构建参数字符串，如本教程所述，如果必须删除最后一个“and”/“或”？@MichaelMarkidis，您还可以使用一个索引循环，并为列表中的最后一项添加一个条件，以不添加“and/or”，但在我看来，这完全是冗长的。

public class Test {
private Test() {

    // each country for its own
    IFilterBuilder filterBuilder = new FilterBuilder();
    filterBuilder
            .country("UK").or()
            .country("FR").or()
            .country("CA").or()
            .country("US").and()
            .number(123).and()
            .number(789);

    String myFilter = filterBuilder.getResult();
    System.out.println(myFilter);


    // or a short version with a helper method
    IFilterBuilder smartFilterBuilder = new FilterBuilder();
    smartFilterBuilder.inAnyCountry("UK", "FR", "CA", "US").and().withNumbers(123, 789);

    String result = smartFilterBuilder.getResult();
    System.out.println(result);
}

public static void main(String[] args) {
    new Test();
}

interface IFilterBuilderBinder {
    IFilterBuilder or();
    IFilterBuilder and();
}

interface IFilterBuilder {
    IFilterBuilderBinder country(String countryName);
    IFilterBuilderBinder number(int number);
    String getResult();

    IFilterBuilderBinder inAnyCountry(String... country);
    IFilterBuilderBinder withNumbers(int... numbers);
}

private final static class FilterBuilder implements IFilterBuilder, IFilterBuilderBinder {
    private String filter = "&filter=";

    public IFilterBuilderBinder country(String countryName) {
        filter += "country='" + countryName + "'";
        return this;
    }

    @Override
    public IFilterBuilderBinder number(int number) {
        filter += "number='" + number + "'";
        return this;
    }

    public String getResult() {
        return filter;
    }

    @Override
    public IFilterBuilderBinder inAnyCountry(String... country) {
        for (int i = 0; i < country.length; i++) {
            country( country[i]);
            if(i!=country.length-1){
                or();
            }
        }
        return this;
    }

    @Override
    public IFilterBuilderBinder withNumbers(int... numbers) {
        for (int i = 0; i < numbers.length; i++) {
            number(numbers[i]);
            if(i!=numbers.length-1){
                and();
            }
        }
        return this;
    }

    @Override
    public IFilterBuilder or() {
        filter += " or ";
        return this;
    }

    @Override
    public IFilterBuilder and() {
        filter += " and ";
        return this;
    }
}