第一章
1、节字符串连接
1、在jdk 8之前版本，可以使用 + 连接字符串
2、StringBuilder 进行append操作
3、string.concat进行操作
4、string format进行插空
5、jdk 8 s可以使用String ,join 进行字符串连接
6、java.util.StringJoiner 操作
7、使用 StringJoiner
8、 using Collectors#joining()
9、Starting with JDK 13/15using text blocks
package chaptor01.P01_TextBlockSQLJSONHTML;
import java.util.StringJoiner;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class Main {
public static void main(String[] args) {
//字符串连接
// 在jdk 8 之前，我们使用+进行字符串连接
System.out.println("Multiline SQL/JSON/HTML before text blocks "
+ "(using concatenation via the '+' operator):");
String sql1
= "UPDATE \"public\".\"office\"\n"
+ "SET (\"address_first\", \"address_second\", \"phone\") =\n"
+ " (SELECT \"public\".\"employee\".\"first_name\",\n"
+ " \"public\".\"employee\".\"last_name\", ?\n"
+ " FROM \"public\".\"employee\"\n"
+ " WHERE \"public\".\"employee\".\"job_title\" = ?";
String json1
= "{\n"
+ " \"widget\": {\n"
+ " \"debug\": \"on\",\n"
+ " \"window\": {\n"
+ " \"title\": \"Sample Widget 1\",\n"
+ " \"name\": \"back_window\"\n"
+ " },\n"
+ " \"image\": {\n"
+ " \"src\": \"images\\sw.png\"\n"
+ " },\n"
+ " \"text\": {\n"
+ " \"data\": \"Click Me\",\n"
+ " \"size\": 39\n"
+ " }\n"
+ " }\n"
+ "}";
String html1
= "<table>\n"
+ " <tr>\n"
+ " <th colspan=\"2\">Name</th>\n"
+ " <th>Age</th>\n"
+ " </tr>\n"
+ " <tr>\n"
+ " <td>John</td>\n"
+ " <td>Smith</td>\n"
+ " <td>22</td>\n"
+ " </tr>\n"
+ "<table>";
System.out.println(sql1);
System.out.println();
System.out.println(json1);
System.out.println();
System.out.println(html1);
// 我们同样可以 StringBuilder 连接 append 连接
System.out.println("\n Multiline SQL/JSON/HTML before text blocks (using StringBuilder):");
StringBuilder sql2 = new StringBuilder();
sql2.append("UPDATE \"public\".\"office\"\n")
.append("SET (\"address_first\", \"address_second\", \"phone\") =\n")
.append(" (SELECT \"public\".\"employee\".\"first_name\",\n")
.append(" \"public\".\"employee\".\"last_name\", ?\n")
.append(" FROM \"public\".\"employee\"\n")
.append(" WHERE \"public\".\"employee\".\"job_title\" = ?;");
StringBuilder json2 = new StringBuilder();
json2.append("{\n")
.append(" \"widget\": {\n")
.append(" \"debug\": \"on\",\n")
.append(" \"window\": {\n")
.append(" \"title\": \"Sample Widget 1\",\n")
.append(" \"name\": \"back_window\"\n")
.append(" },\n")
.append(" \"image\": {\n")
.append(" \"src\": \"images\\sw.png\"\n")
.append(" },\n")
.append(" \"text\": {\n")
.append(" \"data\": \"Click Me\",\n")
.append(" \"size\": 39\n")
.append(" }\n")
.append(" }\n")
.append("}");
StringBuilder html2 = new StringBuilder();
html2.append("<table>\n")
.append(" <tr>\n")
.append(" <th colspan=\"2\">Name</th>\n")
.append(" <th>Age</th>\n")
.append(" </tr>\n")
.append(" <tr>\n")
.append(" <td>John</td>\n")
.append(" <td>Smith</td>\n")
.append(" <td>22</td>\n")
.append(" </tr>\n")
.append("<table>");
System.out.println(sql2);
System.out.println();
System.out.println(json2);
System.out.println();
System.out.println(html2);
// using String#concat()
System.out.println("\n Multiline SQL/JSON/HTML before text blocks (using String#concat()):");
String sql3 = "UPDATE \"public\".\"office\"\n"
.concat("SET (\"address_first\", \"address_second\", \"phone\") =\n")
.concat(" (SELECT \"public\".\"employee\".\"first_name\",\n")
.concat(" \"public\".\"employee\".\"last_name\", ?\n")
.concat(" FROM \"public\".\"employee\"\n")
.concat(" WHERE \"public\".\"employee\".\"job_title\" = ?;");
String json3 = "{\n"
.concat(" \"widget\": {\n")
.concat(" \"debug\": \"on\",\n")
.concat(" \"window\": {\n")
.concat(" \"title\": \"Sample Widget 1\",\n")
.concat(" \"name\": \"back_window\"\n")
.concat(" },\n")
.concat(" \"image\": {\n")
.concat(" \"src\": \"images\\sw.png\"\n")
.concat(" },\n")
.concat(" \"text\": {\n")
.concat(" \"data\": \"Click Me\",\n")
.concat(" \"size\": 39\n")
.concat(" }\n")
.concat(" }\n")
.concat("}");
String html3 = "<table>\n"
.concat(" <tr>\n")
.concat(" <th colspan=\"2\">Name</th>\n")
.concat(" <th>Age</th>\n")
.concat(" </tr>\n")
.concat(" <tr>\n")
.concat(" <td>John</td>\n")
.concat(" <td>Smith</td>\n")
.concat(" <td>22</td>\n")
.concat(" </tr>\n")
.concat("<table>");
System.out.println(sql3);
System.out.println();
System.out.println(json3);
System.out.println();
System.out.println(html3);
// 使用 string format连接
System.out.println("\n Multiline SQL/JSON/HTML before text blocks (using String#format()):");
String sql4 = String.format("%s%s%s%s%s%s",
"UPDATE \"public\".\"office\"\n",
"SET (\"address_first\", \"address_second\", \"phone\") =\n",
" (SELECT \"public\".\"employee\".\"first_name\",\n",
" \"public\".\"employee\".\"last_name\", ?\n",
" FROM \"public\".\"employee\"\n",
" WHERE \"public\".\"employee\".\"job_title\" = ?;");
String json4 = String.format("%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s%s",
"{\n",
" \"widget\": {\n",
" \"debug\": \"on\",\n",
" \"window\": {\n",
" \"title\": \"Sample Widget 1\",\n",
" \"name\": \"back_window\"\n",
" },\n",
" \"image\": {\n",
" \"src\": \"images\\sw.png\"\n",
" },\n",
" \"text\": {\n",
" \"data\": \"Click Me\",\n",
" \"size\": 39\n",
" }\n",
" }\n",
"}");
String html4 = String.format("%s%s%s%s%s%s%s%s%s%s%s",
"<table>\n",
" <tr>\n",
" <th colspan=\"2\">Name</th>\n",
" <th>Age</th>\n",
" </tr>\n",
" <tr>\n",
" <td>John</td>\n",
" <td>Smith</td>\n",
" <td>22</td>\n",
" </tr>\n",
"<table>");
System.out.println(sql4);
System.out.println();
System.out.println(json4);
System.out.println();
System.out.println(html4);
// jdk 8 s可以使用String ,join 进行字符串连接
System.out.println("\n Multiline SQL/JSON/HTML before text blocks (using String#join()):");
String sql5 = String.join("\n",
"UPDATE \"public\".\"office\"",
"SET (\"address_first\", \"address_second\", \"phone\") =",
" (SELECT \"public\".\"employee\".\"first_name\",",
" \"public\".\"employee\".\"last_name\", ?",
" FROM \"public\".\"employee\"",
" WHERE \"public\".\"employee\".\"job_title\" = ?;");
String json5 = String.join("\n",
"{",
" \"widget\": {",
" \"debug\": \"on\",",
" \"window\": {",
" \"title\": \"Sample Widget 1\",",
" \"name\": \"back_window\"",
" },",
" \"image\": {",
" \"src\": \"images\\sw.png\"",
" },",
" \"text\": {",
" \"data\": \"Click Me\",",
" \"size\": 39",
" }",
" }",
"}");
String html5 = String.join("\n",
"<table>",
" <tr>",
" <th colspan=\"2\">Name</th>",
" <th>Age</th>",
" </tr>",
" <tr>",
" <td>John</td>",
" <td>Smith</td>",
" <td>22</td>",
" </tr>",
"<table>");
System.out.println(sql5);
System.out.println();
System.out.println(json5);
System.out.println();
System.out.println(html5);
// 使用 StringJoiner
System.out.println("\n Multiline SQL/JSON/HTML before text blocks (using StringJoiner):");
StringJoiner sql6 = new StringJoiner("\n");
sql6.add("UPDATE \"public\".\"office\"")
.add("SET (\"address_first\", \"address_second\", \"phone\") =")
.add(" (SELECT \"public\".\"employee\".\"first_name\",")
.add(" \"public\".\"employee\".\"last_name\", ?")
.add(" FROM \"public\".\"employee\"")
.add(" WHERE \"public\".\"employee\".\"job_title\" = ?;");
StringJoiner json6 = new StringJoiner("\n");
json6.add("{")
.add(" \"widget\": {")
.add(" \"debug\": \"on\",")
.add(" \"window\": {")
.add(" \"title\": \"Sample Widget 1\",")
.add(" \"name\": \"back_window\"")
.add(" },")
.add(" \"image\": {")
.add(" \"src\": \"images\\sw.png\"")
.add(" },")
.add(" \"text\": {")
.add(" \"data\": \"Click Me\",")
.add(" \"size\": 39")
.add(" }")
.add(" }")
.add("}");
StringJoiner html6 = new StringJoiner("\n");
html6.add("<table>")
.add(" <tr>")
.add(" <th colspan=\"2\">Name</th>")
.add(" <th>Age</th>")
.add(" </tr>")
.add(" <tr>")
.add(" <td>John</td>")
.add(" <td>Smith</td>")
.add(" <td>22</td>")
.add(" </tr>")
.add("<table>");
System.out.println(sql6);
System.out.println();
System.out.println(json6);
System.out.println();
System.out.println(html6);
// using Collectors#joining()
System.out.println("\n Multiline SQL/JSON/HTML before text blocks (using Collectors#joining()):");
String sql7 = Stream.of(
"UPDATE \"public\".\"office\"",
"SET (\"address_first\", \"address_second\", \"phone\") =",
" (SELECT \"public\".\"employee\".\"first_name\",",
" \"public\".\"employee\".\"last_name\", ?",
" FROM \"public\".\"employee\"",
" WHERE \"public\".\"employee\".\"job_title\" = ?;")
.collect(Collectors.joining(String.valueOf("\n")));
String json7 = Stream.of(
"{",
" \"widget\": {",
" \"debug\": \"on\",",
" \"window\": {",
" \"title\": \"Sample Widget 1\",",
" \"name\": \"back_window\"",
" },",
" \"image\": {",
" \"src\": \"images\\sw.png\"",
" },",
" \"text\": {",
" \"data\": \"Click Me\",",
" \"size\": 39",
" }",
" }",
"}")
.collect(Collectors.joining(String.valueOf("\n")));
String html7 = Stream.of(
"<table>",
" <tr>",
" <th colspan=\"2\">Name</th>",
" <th>Age</th>",
" </tr>",
" <tr>",
" <td>John</td>",
" <td>Smith</td>",
" <td>22</td>",
" </tr>",
"<table>")
.collect(Collectors.joining(String.valueOf("\n")));
System.out.println(sql7);
System.out.println();
System.out.println(json7);
System.out.println();
System.out.println(html7);
// Starting with JDK 13/15
// using text blocks
System.out.println("\n Multiline SQL/JSON/HTML using text blocks:");
String sql8 = """
UPDATE "public"."office"
SET ("address_first", "address_second", "phone") =
(SELECT "public"."employee"."first_name",
"public"."employee"."last_name", ?
FROM "public"."employee"
WHERE "public"."employee"."job_title" = ?""";
String json8 = """
{
"widget": {
"debug": "on",
"window": {
"title": "Sample Widget 1",
"name": "back_window"
},
"image": {
"src": "images\\sw.png"
},
"text": {
"data": "Click Me",
"size": 39
}
}
}""";
String html8 = """
<table>
<tr>
<th colspan="2">Name</th>
<th>Age</th>
</tr>
<tr>
<td>John</td>
<td>Smith</td>
<td>22</td>
</tr>
<table>""";
System.out.println(sql8);
System.out.println();
System.out.println(json8);
System.out.println();
System.out.println(html8);
}
}2、举例说明文本块分隔符的用法
这个语法跟python的类似
public class Main {
public static void main(String[] args) {
System.out.println("The common usage of text block delimiters:\n");
String sql1 = """
UPDATE "public"."office"
SET ("address_first", "address_second", "phone") =
(SELECT "public"."employee"."first_name",
"public"."employee"."last_name", ?
FROM "public"."employee"
WHERE "public"."employee"."job_title" = ?""";
System.out.println("-- BEFORE TEXT BLOCK --");
System.out.println(sql1);
System.out.println("-- AFTER TEXT BLOCK --");
System.out.println("\nKeep the opening delimiter and the content on the "
+ "same line is not accepted (does not compile)\n");
/*
String not_compile = """UPDATE "public"."office"
SET ("address_first", "address_second", "phone") =
(SELECT "public"."employee"."first_name",
"public"."employee"."last_name", ?
FROM "public"."employee"
WHERE "public"."employee"."job_title" = ?""";
*/
System.out.println("\nShift-left the content has no effect:\n");
String sql2 = """
UPDATE "public"."office"
SET ("address_first", "address_second", "phone") =
(SELECT "public"."employee"."first_name",
"public"."employee"."last_name", ?
FROM "public"."employee"
WHERE "public"."employee"."job_title" = ?""";
System.out.println("-- BEFORE TEXT BLOCK --");
System.out.println(sql2);
System.out.println("-- AFTER TEXT BLOCK --");
System.out.println("\nShift-right the opening/closing delimiter has no effect:\n");
String sql3 = """
UPDATE "public"."office"
SET ("address_first", "address_second", "phone") =
(SELECT "public"."employee"."first_name",
"public"."employee"."last_name", ?
FROM "public"."employee"
WHERE "public"."employee"."job_title" = ? """;
System.out.println("-- BEFORE TEXT BLOCK --");
System.out.println(sql3);
System.out.println("-- AFTER TEXT BLOCK --");
System.out.println("\nMoving the closing delimiter on its own line (1):\n");
String sql4 = """
UPDATE "public"."office"
SET ("address_first", "address_second", "phone") =
(SELECT "public"."employee"."first_name",
"public"."employee"."last_name", ?
FROM "public"."employee"
WHERE "public"."employee"."job_title" = ?
""";
System.out.println("-- BEFORE TEXT BLOCK --");
System.out.println(sql4);
System.out.println("-- AFTER TEXT BLOCK --");
System.out.println("\nMoving the closing delimiter on its own line (2):\n");
String sql5 = """
UPDATE "public"."office"
SET ("address_first", "address_second", "phone") =
(SELECT "public"."employee"."first_name",
"public"."employee"."last_name", ?
FROM "public"."employee"
WHERE "public"."employee"."job_title" = ?
""";
System.out.println("-- BEFORE TEXT BLOCK --");
System.out.println(sql5);
System.out.println("-- AFTER TEXT BLOCK --");
System.out.println("\nMoving on its own line and shift-left the closing delimiter:\n");
String sql6 = """
UPDATE "public"."office"
SET ("address_first", "address_second", "phone") =
(SELECT "public"."employee"."first_name",
"public"."employee"."last_name", ?
FROM "public"."employee"
WHERE "public"."employee"."job_title" = ?
""";
System.out.println("-- BEFORE TEXT BLOCK --");
System.out.println(sql6);
System.out.println("-- AFTER TEXT BLOCK --");
System.out.println("\nMoving on its own line and shift-right the closing delimiter:\n");
String sql7 = """
UPDATE "public"."office"
SET ("address_first", "address_second", "phone") =
(SELECT "public"."employee"."first_name",
"public"."employee"."last_name", ?
FROM "public"."employee"
WHERE "public"."employee"."job_title" = ?
""";
System.out.println("-- BEFORE TEXT BLOCK --");
System.out.println(sql7);
System.out.println("-- AFTER TEXT BLOCK --");
}
}