时间:2021-07-01 10:21:17 帮助过:4人阅读
- <span style="color: #0000ff">package</span><span style="color: #000000"> com.test.properties;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.File;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.IOException;
- </span><span style="color: #0000ff">public</span> <span style="color: #0000ff">class</span><span style="color: #000000"> TestProperties {
- </span><span style="color: #0000ff">private</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">final</span> String dataSourcePath = "resources/dataSource.properties"<span style="color: #000000">;
- </span><span style="color: #0000ff">private</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">final</span><span style="color: #000000"> String
- absoluteDataSourcePath </span>= "D:\\Workspace\\Blogs\\TEST_Preparedstatement\\resources\\dataSource.properties"<span style="color: #000000">;
- </span><span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span><span style="color: #000000"> main(String[] args) {
- </span><span style="color: #0000ff">try</span><span style="color: #000000"> {
- </span><span style="color: #008000">//</span><span style="color: #008000"> 1.getPath() 方法跟创建 File 对象时传入的路径参数有关,返回构造时传入的路径
- </span><span style="color: #008000">//</span><span style="color: #008000"> 2.getAbsolutePath() 方法返回文件的绝对路径,如果构造的时候是全路径就直接返回全路径,
- </span><span style="color: #008000">//</span><span style="color: #008000"> 如果构造时是相对路径,就返回当前目录的路径 + 构造 File 对象时的路径
- </span><span style="color: #008000">//</span><span style="color: #008000"> 3.getCanonicalPath() 方法返回绝对路径,会把 ..\ 、.\ 这样的符号解析掉
- </span><span style="color: #008000">//</span><span style="color: #008000"> 1.相对路径读取文件
- </span><span style="color: #008000">//</span><span style="color: #008000">user.dir为当前用户目录(即项目路径),java.io 包中的类总是根据当前用户目录来解析相对路径名,
- </span><span style="color: #008000">//</span><span style="color: #008000">当File对象入参不是以"/"开始的时候,则判断为相对路径方式构造,使用当前用户目录+相对路径的方式构造文件对象</span>
- System.out.println("当前用户目录:" + System.getProperty("user.dir"<span style="color: #000000">));
- File file </span>= <span style="color: #0000ff">new</span><span style="color: #000000"> File(dataSourcePath);
- System.out.println(</span>"入参路径:" + file.getPath());<span style="color: #008000">//</span><span style="color: #008000">入参路径</span>
- System.out.println("绝对路径:" + file.getAbsolutePath());<span style="color: #008000">//</span><span style="color: #008000">绝对路径</span>
- System.out.println("绝对路径:" + file.getCanonicalPath());<span style="color: #008000">//</span><span style="color: #008000">绝对路径
- </span><span style="color: #008000">//</span><span style="color: #008000"> 2.绝对路径读取文件
- </span><span style="color: #008000">//</span><span style="color: #008000">绝对路径名:是完整的路径名,从根目录定位文件位置,不需要参照其他文件路径,
- </span><span style="color: #008000">//</span><span style="color: #008000">windows中从某个分区磁盘如"c:</span><span style="color: #008000">//</span><span style="color: #008000">"开始定位,linux表示从根目录"/"开始定位。</span>
- File file2 = <span style="color: #0000ff">new</span><span style="color: #000000"> File(absoluteDataSourcePath);
- System.out.println(</span>""<span style="color: #000000">);
- System.out.println(</span>"入参路径2:" + file2.getPath());<span style="color: #008000">//</span><span style="color: #008000">入参路径</span>
- System.out.println("绝对路径2:" + file2.getAbsolutePath());<span style="color: #008000">//</span><span style="color: #008000">绝对路径</span>
- System.out.println("绝对路径2:" + file2.getCanonicalPath());<span style="color: #008000">//</span><span style="color: #008000">绝对路径</span>
- } <span style="color: #0000ff">catch</span><span style="color: #000000"> (IOException e) {
- </span><span style="color: #008000">//</span><span style="color: #008000"> TODO Auto-generated catch block</span>
- <span style="color: #000000"> e.printStackTrace();
- }
- }
- }</span>
下面截图是控制台输出的结果:对应的解释我都写在代码的注释里了。
搞清楚了绝对路径和相对路径,我们就可以借助java.util包中的Properties来读取项目中的配置文件了,下面是常用的三种方法:
1.其中第一种方法在上面的相对路径读取文件中也讲了,这里使用相对路径,java.io解析时会自动加上项目路径,也就是说等于是绝对路径,这里也可以使用绝对路径,但项目不推荐这样做是因为指定死了盘符,项目移动别的系统平台时就要改动。
2.第2、3种方法大同小异,就是要注意下class时使用加”/”是classes根目录下,所以要加”/”,而getClassLoader时直接是获得的classPath,所以不需要加根目录”/”
- <span style="color: #0000ff">package</span><span style="color: #000000"> com.test.preparedstatement;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.BufferedInputStream;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.File;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.FileInputStream;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.FileNotFoundException;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.IOException;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.InputStream;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.util.Properties;
- </span><span style="color: #0000ff">public</span> <span style="color: #0000ff">class</span><span style="color: #000000"> TestJdbc {
- </span><span style="color: #0000ff">private</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">final</span> String dataSourcePath = "resources/dataSource.properties"<span style="color: #000000">;
- </span><span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span><span style="color: #000000"> getPathByJavaUtilProperties() {
- </span><span style="color: #0000ff">try</span><span style="color: #000000"> {
- </span><span style="color: #008000">//</span><span style="color: #008000"> 1.使用java.util.Properties类的load(InputStream in)方法加载properties文件</span>
- InputStream iStream = <span style="color: #0000ff">new</span> BufferedInputStream(<span style="color: #0000ff">new</span> FileInputStream(<span style="color: #0000ff">new</span><span style="color: #000000"> File(dataSourcePath)));
- Properties properties </span>= <span style="color: #0000ff">new</span><span style="color: #000000"> Properties();
- properties.load(iStream);
- System.out.println(</span>"用户名1:" + properties.getProperty("username"<span style="color: #000000">));
- System.out.println(</span>""<span style="color: #000000">);
- </span><span style="color: #008000">//</span><span style="color: #008000"> getResourceAsStream()参数与getResouce()是一样的,它相当于你用getResource()取得File文件后,
- </span><span style="color: #008000">//</span><span style="color: #008000"> 再new InputStream(file)一样的结果
- </span><span style="color: #008000">//</span><span style="color: #008000"> 2.使用class变量的getResourceAsStream()方法</span>
- Properties properties2 = <span style="color: #0000ff">new</span><span style="color: #000000"> Properties();
- InputStream iStream2 </span>= TestJdbc.<span style="color: #0000ff">class</span>.getResourceAsStream("/dataSource.properties"<span style="color: #000000">);
- </span><span style="color: #008000">//</span><span style="color: #008000"> 这里为什么入参是加"/"的呢?,看一下下面的输出就明白了,Object是以class文件开始定位的</span>
- System.out.println(TestJdbc.<span style="color: #0000ff">class</span>.getResource(""));<span style="color: #008000">//</span><span style="color: #008000">从编译根目录下的包目录下取</span>
- System.out.println(TestJdbc.<span style="color: #0000ff">class</span>.getResource("/"));<span style="color: #008000">//</span><span style="color: #008000">获取编译目录的根目录classes</span>
- <span style="color: #000000"> properties2.load(iStream2);
- System.out.println(</span>"用户名2:" + properties2.getProperty("username"<span style="color: #000000">));
- System.out.println(</span>""<span style="color: #000000">);
- </span><span style="color: #008000">//</span><span style="color: #008000"> 3.使用class.getClassLoader()的getResourceAsStream()方法</span>
- Properties properties3 = <span style="color: #0000ff">new</span><span style="color: #000000"> Properties();
- InputStream iStream3 </span>= TestJdbc.<span style="color: #0000ff">class</span>.getClassLoader().getResourceAsStream("dataSource.properties"<span style="color: #000000">);
- </span><span style="color: #008000">//</span><span style="color: #008000">这里又为什么不加"/",还是输出一下看,Object.class.getClassLoader()则是以classPath定位,所以不需要加"/"</span>
- System.out.println(TestJdbc.<span style="color: #0000ff">class</span>.getClassLoader().getResource(""<span style="color: #000000">));
- System.out.println(TestJdbc.</span><span style="color: #0000ff">class</span>.getClassLoader().getResource("/"<span style="color: #000000">));
- properties3.load(iStream3);
- System.out.println(</span>"用户名3:" + properties3.getProperty("username"<span style="color: #000000">));
- System.out.println(</span>""<span style="color: #000000">);
- } </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (FileNotFoundException e) {
- e.printStackTrace();
- } </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (IOException e) {
- e.printStackTrace();
- }
- }
- </span><span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span><span style="color: #000000"> main(String[] args) {
- TestJdbc.getPathByJavaUtilProperties();
- </span><span style="color: #008000">//</span><span style="color: #008000"> TestJdbc.getDataBaseData();</span>
- <span style="color: #000000"> }
- }</span>
下面是输出结果,这里要注意TestJdbc.class.getClassLoader().getResource("/")是null
加载好配置文件后,我来测试一下jdbc连接mysql数据库时,批量插入数据使用statement和preparedStatement效率,不多比比,代码来说话:
- <span style="color: #0000ff">package</span><span style="color: #000000"> com.test.preparedstatement;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.BufferedInputStream;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.File;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.FileInputStream;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.FileNotFoundException;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.IOException;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.io.InputStream;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.Connection;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.DriverManager;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.PreparedStatement;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.SQLException;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.sql.Statement;
- </span><span style="color: #0000ff">import</span><span style="color: #000000"> java.util.Properties;
- </span><span style="color: #0000ff">public</span> <span style="color: #0000ff">class</span><span style="color: #000000"> TestJdbc {
- </span><span style="color: #0000ff">private</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">final</span> String dataSourcePath = "resources/dataSource.properties"<span style="color: #000000">;
- </span><span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span><span style="color: #000000"> getDataBaseData() {
- </span><span style="color: #0000ff">try</span><span style="color: #000000"> {
- InputStream iStream </span>= <span style="color: #0000ff">new</span> BufferedInputStream(<span style="color: #0000ff">new</span> FileInputStream(<span style="color: #0000ff">new</span><span style="color: #000000"> File(dataSourcePath)));
- Properties properties </span>= <span style="color: #0000ff">new</span><span style="color: #000000"> Properties();
- properties.load(iStream);
- String username </span>= properties.getProperty("username"<span style="color: #000000">);
- String password </span>= properties.getProperty("password"<span style="color: #000000">);
- String driver </span>= properties.getProperty("driver"<span style="color: #000000">);
- String url </span>= properties.getProperty("url"<span style="color: #000000">);
- </span><span style="color: #008000">//</span><span style="color: #008000"> 1.statement方式</span>
- <span style="color: #0000ff">long</span> start =<span style="color: #000000"> System.currentTimeMillis();
- </span><span style="color: #008000">//</span><span style="color: #008000">加载驱动</span>
- <span style="color: #000000"> Class.forName(driver);
- </span><span style="color: #008000">//</span><span style="color: #008000">建立连接</span>
- Connection connection =<span style="color: #000000"> DriverManager.getConnection(url, username, password);
- </span><span style="color: #008000">//</span><span style="color: #008000">创建statement</span>
- Statement statement =<span style="color: #000000"> connection.createStatement();
- </span><span style="color: #0000ff">for</span> (<span style="color: #0000ff">int</span> i = 0; i < 50; i++<span style="color: #000000">) {
- statement.execute(</span>"insert into test values("+i+",‘a"+i+"‘)"<span style="color: #000000">);
- }
- statement.close();
- connection.close();
- System.out.println(</span>"statment花费时间:"+String.valueOf(System.currentTimeMillis()-<span style="color: #000000">start));
- </span><span style="color: #008000">//</span><span style="color: #008000"> 2.preparedStatement方式</span>
- <span style="color: #0000ff">long</span> start2 =<span style="color: #000000"> System.currentTimeMillis();
- </span><span style="color: #008000">//</span><span style="color: #008000">加载驱动</span>
- <span style="color: #000000"> Class.forName(driver);
- </span><span style="color: #008000">//</span><span style="color: #008000">建立连接</span>
- Connection connection2 =<span style="color: #000000"> DriverManager.getConnection(url, username, password);
- </span><span style="color: #008000">//</span><span style="color: #008000">创建preparedStatement</span>
- PreparedStatement preparedStatement = connection2.prepareStatement("insert into test values(?,?)"<span style="color: #000000">);
- </span><span style="color: #0000ff">for</span> (<span style="color: #0000ff">int</span> j = 50; j < 100; j++<span style="color: #000000">) {
- preparedStatement.setInt(</span>1<span style="color: #000000">, j);
- preparedStatement.setString(</span>2, "b"+<span style="color: #000000">j);
- preparedStatement.execute();
- }
- preparedStatement.close();
- connection2.close();
- System.out.println(</span>"preparedStatement花费时间:"+String.valueOf(System.currentTimeMillis()-<span style="color: #000000">start2));
- } </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (FileNotFoundException e) {
- e.printStackTrace();
- } </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (IOException e) {
- e.printStackTrace();
- } </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (ClassNotFoundException e) {
- e.printStackTrace();
- } </span><span style="color: #0000ff">catch</span><span style="color: #000000"> (SQLException e) {
- e.printStackTrace();
- }
- }
- </span><span style="color: #0000ff">public</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span><span style="color: #000000"> main(String[] args) {
- TestJdbc.getDataBaseData();
- }
- }</span>
数据库数据插入了100条数据,执行成功:
然后看看控制台执行时间比较:
可以看到statement执行时间是preparedstatement执行时间的3倍,在批量处理上,preparedstatement效率更高。
prepared是准备的意思,也就是mysql的预编译在起作用。
1.使用statement时,每次执行sql,statement都会直接把sql扔给数据库执行,而且每次执行都要经过编译sql,执行sql,获得结果的过程,50次操作,50次编译。
2.preparedstatement不同的是在创建preparedstatement对象时就把sql语句结构输入进去了,并把这个sql预编译成函数并保存起来,然后加载参数,执行sql,返回结果。当批量处理时,后面49个处理都是使用这个函数,因为sql结构没变,所以不用二次编译,直接赋值,执行。
3.PreparedStatement继承自Statement,可以说对statement做了优化
4.下面这句是网上说的,具体我没测过:JDBC驱动程序5.0.5以后版本 默认预编译都是关闭的。jdbc:mysql://localhost:3306/mybatis?&useServerPrepStmts=true&cachePrepStmts=tru在MySQL中,既要开启预编译也要开启缓存。因为如果只是开启预编译的话效率还没有不开启预编译效率高。
5.因为preparedstatement使用?作占位符,所以就算恶意的sql进入到后台,在preparedStatement.execute();之前已经对sql做了预编译,就是说sql的执行函数已经确定,所以不会再破坏sql的结构。所以可以防止sql注入。
回头探索JDBC及PreparedStatement防SQL注入原理
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