Accessing Relational Data using

如果不知道如何使用 Spring，请先查看 Building a RESTful Web Service。

官方文章地址：https://spring.io/guides/gs/relational-data-access/

实现示例：使用 JdbcTemplate 访问关系型数据库。
下载地址：

git clone https://github.com/spring-guides/gs-relational-data-access.git

build.gradle 文件：

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:1.5.3.RELEASE")
    }
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'idea'
apply plugin: 'org.springframework.boot'

jar {
    baseName = 'gs-relational-data-access'
    version =  '0.1.0'
}

repositories {
    mavenCentral()
}

sourceCompatibility = 1.8
targetCompatibility = 1.8

dependencies {
    compile("org.springframework.boot:spring-boot-starter")
    compile("org.springframework:spring-jdbc")
    compile("com.h2database:h2")
    testCompile("junit:junit")
}

创建 src/main/java/hello/Customer.java，里面包括 id，firstName、lastName:

package hello;

public class Customer {
    private long id;
    private String firstName, lastName;

    public Customer(long id, String firstName, String lastName) {
        this.id = id;
        this.firstName = firstName;
        this.lastName = lastName;
    }

    @Override
    public String toString() {
        return String.format(
                "Customer[id=%d, firstName='%s', lastName='%s']",
                id, firstName, lastName);
    }

    // getters & setters omitted for brevity
}

src/main/java/hello/Application.java：

package hello;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.jdbc.core.JdbcTemplate;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

@SpringBootApplication
public class Application implements CommandLineRunner {

    private static final Logger log = LoggerFactory.getLogger(Application.class);

    public static void main(String args[]) {
        SpringApplication.run(Application.class, args);
    }

    @Autowired
    JdbcTemplate jdbcTemplate;

    @Override
    public void run(String... strings) throws Exception {

        log.info("Creating tables");

        jdbcTemplate.execute("DROP TABLE customers IF EXISTS");
        jdbcTemplate.execute("CREATE TABLE customers(" +
                "id SERIAL, first_name VARCHAR(255), last_name VARCHAR(255))");

        // Split up the array of whole names into an array of first/last names
        List<Object[]> splitUpNames = Arrays.asList("John Woo", "Jeff Dean", "Josh Bloch", "Josh Long").stream()
                .map(name -> name.split(" "))
                .collect(Collectors.toList());

        // Use a Java 8 stream to print out each tuple of the list
        splitUpNames.forEach(name -> log.info(String.format("Inserting customer record for %s %s", name[0], name[1])));

        // Uses JdbcTemplate's batchUpdate operation to bulk load data
        jdbcTemplate.batchUpdate("INSERT INTO customers(first_name, last_name) VALUES (?,?)", splitUpNames);

        log.info("Querying for customer records where first_name = 'Josh':");
        jdbcTemplate.query(
                "SELECT id, first_name, last_name FROM customers WHERE first_name = ?", new Object[] { "Josh" },
                (rs, rowNum) -> new Customer(rs.getLong("id"), rs.getString("first_name"), rs.getString("last_name"))
        ).forEach(customer -> log.info(customer.toString()));
    }
}

Spring 支持 H2，一个在内存中实现关系型数据库的库，并且自动创建连接。使用 spring-jdbc，Spring Boot 会自动创建 JdbcTemplate，@Autowired JdbcTemplate 自动加载 JdbcTemplate 并使其可用。

Application 实现了 CommandLineRunner，应用启动好后会自动执行 run() 方法。

使用 JdbcTemplate’sexecute` 执行 DDL（数据库定义语言）。

想数据库中插入许多数据使用 JdbcTemplate.batchUpdate，插入一条数据使用 JdbcTemplate.insert。

使用 ? 可防止 SQL injection attacks(SQL 注入攻击)。

执行结果如下：

2017-06-11 17:07:33.909  INFO 7139 --- [           main] hello.Application                        : Creating tables
2017-06-11 17:07:33.952  INFO 7139 --- [           main] hello.Application                        : Inserting customer record for John Woo
2017-06-11 17:07:33.952  INFO 7139 --- [           main] hello.Application                        : Inserting customer record for Jeff Dean
2017-06-11 17:07:33.952  INFO 7139 --- [           main] hello.Application                        : Inserting customer record for Josh Bloch
2017-06-11 17:07:33.952  INFO 7139 --- [           main] hello.Application                        : Inserting customer record for Josh Long
2017-06-11 17:07:33.985  INFO 7139 --- [           main] hello.Application                        : Querying for customer records where first_name = 'Josh':
2017-06-11 17:07:33.992  INFO 7139 --- [           main] hello.Application                        : Customer[id=3, firstName='Josh', lastName='Bloch']
2017-06-11 17:07:33.992  INFO 7139 --- [           main] hello.Application                        : Customer[id=4, firstName='Josh', lastName='Long']